How did Ernest Rutherford discover the nucleus|Rutherford Model of atom

How did Ernest Rutherford discover the nucleus|Rutherford Model of atom


How did Ernest Rutherford discover the nucleus

Hello friends,  welcome to our blog, today we are going to discuss how did Sir Rutherford discovered the nucleus. In 1911, Rutherford performed alpha
(α) ray scattering experiment to know about the position of fundamental particles electron, proton in an atom. The alpha(α) particles were obtained form the radioactive element radium enclosed in the box of lead. After passing through a slit, the particles in the form of rays were made to strike against the very thin foil(4*10-5 cm thick) of heavy metal like gold. These particle got scattered and were made to fall on circular screen coated with zinc sulphide(ZnS). They produce flashes of light (also known as scintillation) on screen this help in identifying these particles.

From the experiment, Rutherford made the following observations

1. Most of the alpha particles (99%) passed through gold foil undeflected.

2. Some of these particles be deflected by small angles.

3. A very few alpha particles (one out of 20,000 particles) suffered major deflections by more than 90° and even came back in same direction.

Conclusion from the observation 

The scattering experiment was performed on the gold foil consisting of atoms of gold closely packed in a space and arranged in layers. Rutherford was of the opinion that
most of the alpha particles passed through atom of gold.This means that did not come across any path interrupt.

1. Most of the space inside the atom is expected to be empty. The electrons are negligible mass was supposed be present in this space.
2. As a few of alpha particles suffered from minor deflections and are very few even major deflections, this means that they must have come across some obstruction in their path which must be very small(nucleus contains charge that repel positive charge alpha particle).

Rutherford regarded this(nucleus) small, heavy and positively charged portion inside the atom as a nucleus.All the positive charge protons was supposed to be present in the nucleus and they also accounted for its mass.Some of the space around the nucleus is called extra nuclear portion and all the electrons were supposed to be present in it.


 Rutherford further stated the electron present in extra nuclear portion did not offer any objection to alpha particles and therefore most of them could pass undeflected.

Rutherford Model of atom

In the light of alpha Ray scattering experiment, Rutherford gave the following picture of an atom.

1. An atom consists of two parts nucleus and extra nuclear portion

2.Nucleus is present in the centre of atom. It is massive positively charged also extremely small in size. The radius of nucleus is about 10-15 m. while the atom is about 10-10 m. The size of nucleus is very small as compared to that of atom.

3. Positive charge of the nucleus is due to protons in the atoms. Since the atoms differ in  number of protons therefore,  the magnitude of positive charge on nucleus differ from atom to atom.

4. Extra nuclear portion is a space around the nucleus in which all the electrons are present.

5. Total positive charge of the nucleus is equal to the total net charge of  electrons and the atom as a whole electrically neutral.

6. Electrons in the extra nuclear portion are not stationery but are revolving around the nucleus at a very highest speed in a circular path called orbits. The revolving electrons have certain centrifugal force acting away from the nucleus which balance  the force of attraction directed towards nucleus.

The model of an atom is similar to the solar system where the nucleus is like a sun and electrons may be compared to the planets. The electrons are therefore, called as planetary electrons.
Covalent bond With Examples

Covalent bond With Examples

                   Covalent bond

Hello friends, welcome to our blog, today we are going to discuss the covalent bond. We know that bond means two or more things tie together.Bond may be of different types.

Electrons in a covalent bond

In the formation of molecule only the electrons present in outermost shell or valence shell of atoms normally participate while the electron belongs to inner energy shell are mostly not involved in the bond formation.

Remember: A bond will form only when combining atoms have minimum energy and maximum stability.This will possible if the atom complete the octet (8 electrons in outermost shell) and achieve the electronic configuration of nearest noble gas atom.

In  covalent bond the combining atoms mutually contribute one, two or three electrons depending upon their requirement the bond formed.This leads the formation of single double and triple bond.

Covalent nond is generally present in the atoms of non metal. This may be either same or different. In case of atoms are same the covalent molecule is known as homoatomic and if the combining atoms are different then it is called as heteroatomic molecules

Homoatomic molecules(non polar covalent): The simplest among them is hydrogen Hmolecule in which both the participating atoms have one electron each initially, share there electron and both achieve the stable electronic configuration.

Another example:Chlorine molecule  Cl2 .In this case both the chlorine atoms that is equals to (atomic no 17) have 7 valance electron and a short of one electron each.They share one electron pair which is an electron is contributed by both the atoms to achieve nearest noble gas configuration.


The electron pair belonging to individual atoms not involving sharing called as lone pair (example:oxygen molecule).

Homoatomic molecules(polar covalent): In this case the atom taking part in bond formation belongs to different elements. A few examples of heteroatomic molecules are:
 



It should be noted that this the structure of  molecules or ions in which shared electrons are represented by the dots are known as Lewis dot structure. While those in which these are indicated by line or dashed are called as Couper structures.

How do ionic bonds form|With Examples|Factor Influencing

How do ionic bonds form|With Examples|Factor Influencing

Ionic bond

Hello friends, welcome to our blog. Today we are going to discuss ionic bond. An ionic bond is also called as electrovalent bond.

How do ionic bonds form

In the formation of molecules only electrons present in outermost shell or valence shell of atom normally participate while the electrons belonging to inner energy shell are mostly not involved in the formation of bond.

An ionic bond is formed when there is complete the transfer of one or more electrons from one atom to another.

Bond between metal and nonmetal

 It is generally formed between the metals and non-metals.The metal atom loses one or more electrons present in its valence shell and these electrons are taken up by the non-metallic atom.

Since, the atoms are electrically neutral (electrons and proton are equal in number),by losing electrons,the metal atom changes to positive ion or cation.Similarly, the non-metal atom gaining the electrons, get converted to negative Ion or anion. The opposite charged ions are attracted towards each other and therefore,  come closer resulting the formation of ionic bond (electrovalent Bond).Thus, ionic or electrovalent bond may be defined as :

Definition

 The coulombic or electrostatic force of attraction which hold the opposite charged ions together.

NaCl bond

Formation of sodium chloride (NACl). Sodium atom (Z=11) has one valence electron(2, 8, 1). Similarly chlorine atom (Z=17) has a 7 valance electron (2,8,7). Sodium atom loses its only valence electron and changes  Na+ ion(cation). This electron is taken up by chlorine atom which changes to a Cl- ion(anion).Both of these ions are mutually attracted to form NaCl molecule.


Na +  ion has the configuration of Ne while Cl- ion represent configuration of Ar. Both are inert gas atoms.These the atoms take part in chemical combination or bond formation in order to complete the octet( 8 electron in valance shell) and achieve the electronic configuration of nearest noble gas atom.

Formation of calcium fluoride(CaF2 ).Calcium atom (Z=20) has two valence electron (2,8,8,2). while fluorine atom (Z=9) has seven valence electron in its valence shell (2,7).Now,Ca atom wants to get rid of both valence electrons but each fluorine atom is in position to take up one electron only, This means that these electrons are accepted by two fluorine atoms as shown below.



Ca 2 + ion has electronic configuration of inert gas argon while F- ion has the electronic configuration of neon.

Electrovalency:

It is defined as the number of electrons which an atom lose or gain in the formation of ionic bond.

Actually, electrovalency of an atom is in number of unit charges(positive or negative) on the ion in an ionic bond. If the unit charges are positive, electrovalency is positive. Similarly, electrovalency is negative in case these are the negative. for example in CaF2 electrovalency of calcium is 2(positive) and the fluorine is 1 (negative)

Factor influencing the ionic bond formation

We have learnt that in bond formation one atom loses one or more electrons while the other accept them. As a result cation and anion formed .They mutually attracted by the electrostatic force of attraction result the formation of ionic bond. According to Kossel's scientist ionic bond depends upon the following factors:

Ionization enthalpy

 The amount of energy required to remove the loosely bound electron from an atom is called ionization enthalpy.

 Lesser the ionization enthalpy required easy form of cation.The alkali metals and alkaline earth metals present in s- block normally form cation since they have comparatively low ionization enthalpy.

Electron gain enthalpy

The electron released  in the formation of cation are to be accepted by the other atoms taking part in the ionic bond formation.The electron accepting tendency of an atom depends upon electron gain enthalpy. It may be defined as:
 energy released when an isolated (gaseous) atom take up electron to form anion.

Greater the negative electron gain enthalpy , easier will be the formation of anion. The Halogen present in group 17 have the maximum tendency to form anions as they have very high negative electron gain enthalpy.
The members of group 16 oxygen family such as Oxygen also forms in anion. It has lesser negative electron gain enthalpy then group 17 because it has lesser tendency to form anion.

Lattice energy or enthalpy

The ionic compound exist as crystalline solid and arrangement is called as crystal lattice. Since the ions of charged species, energy (known as lattice energy) is released in the attraction of ions so it may define as:

Energy released when 1 mole of crystalline solid is formed by the combination of oppositely charged ions.

 Greater the magnitude of lattice energy more will be the stability of ionic bond. Ionic compounds

the lattice energy depends upon the following factors:

Size of ion:- The size of ion influence the lattice energy. Smallest size lesser will be the internuclear distance and thus, greater will be the lattice energy. For example: lattice energy of NaCl is more than KCL because the radius of Na + is smaller as compared to K+ ion.

Charge on the ion:-Greater the magnitude of charge on ions higher will be the inter ionic attraction and thus,greater will be the higher value of lattice energy.

So, we conclude that if the magnitude of lattice energy and the negative electron gain enthalpy is greater than that of the ionization enthalpy required, a stable chemical bond will be formed in case it is less than the bond will not form.

General characteristics of ionic bond

1. Melting and boiling point: Because of strong inter ionic forces the ionic compound have generally high melting and boiling point.

2.Solubility: Ionic compounds generally dissolve in polar solvent (like water). Actually in such solvent the polar(water) molecule interact with the ions of crystalline solid(NaCl salt) energy is released. Then the energy released is known as hydration energy and the energy released overcome(weakened) electrostatic force between ions thus get separated and go into the solution. The ionic compound do not dissolve in organic solvent like Benzene carbon tetra chloride because they are non polar in nature.

3.Ionic reactions :The ionic compound the reacts each other through ions which are formed in the solution. Therefore,these take part in ionic reaction which are very fast and do not required any specific condition. For example aqueous solution of NaCl and AgNO3 are mixed a white precipitate of AgCl is immediately formed.

Metallic Bond and types|A metallic bond is a bond between

Metallic Bond and types|A metallic bond is a bond between

Metallic Bond

Hello friends, welcome to our blog, today we are going to discuss metallic bond. Most metal crystallize in close- packet structures. Strong electron interaction among 8 to 12 nearest neighbour atoms (called as coordination number) develop the ability in metals to conduct electricity and heat.


A metallic bond is a bond between

 Bonding in metals is called as metallic bonding. Bonding in metals result from electrical attraction among  positive charge metal ions and mobile, delocalised electrons belonging to Crystal as a whole.

Two models are considered to explain metallic bonding:

1.Band model
2.Electron Sea model

Band Model.

The interaction of two atomic orbitals, say 3s- orbitals of  two sodium atoms,produces two molecular orbitals, one bonding orbitals and one antibonding orbitals .If N atomic orbitals interact , N molecular orbitals are formed. Atoms interact more strongly with nearby atoms than those of farther away. The energy that separates bonding and antibonding molecular orbitals decreases as the interaction (overlap) between the atomic orbital decreases. When we consider all the possible interactions among one mole of  Na atoms, there is a formation of series of very close spaced molecular orbitals(3σ s and 3σ*s (sigma star)). This consists of nearly continuous band of orbitals belonging to crystal as a whole. One mole of Na atoms contributes one mole(6.022×10 23 )of Valence Electrons thus,6.022×10 23 orbitals in the band are half filled.

The empty 3p  atomic orbitals of sodium atoms also interact to form a wide band of 
3* 6.0710 23  orbitals.The 3s and 3p atomic orbitals are quite close in energy, so that these bands of a molecular orbital overlap. The two overlapping band contains 4 *6.0710 23 orbitals. Because each orbital can hold two electrons, the resulting  combination of full bands is only one eighth full.


According to the band theory, the highest energy electrons of metallic crystals occupy  either fully band or partially band that overlap an empty band. A band within which(or into which) electrons must move to allow electrical conduction is called conduction band. The electrical conductivity of metal decreases as temperature increases. The increase in temperature causes  thermal agitation of metal ions.This impends the flow of electrons when an electric field is applied.
Crystalline nonmetals ,such as diamond and phosphorus are insulators, they do not conduct electricity if it is due to the fact that their is highest energy electrons occupy filled bands of molecular orbitals that are separated from the lowest empty band (conduction band) by the energy difference called the band gap.In insulated ,this band  is in an energy different that is too large for him to jump to get the conduction band.


Elements that are semiconductors have filled  bands that are only slightly below, but do not overlap with empty band.They do not conduct electricity at low temperature but small increase in temperature sufficient to excite some of the electron and jump into the highest energy band conduction band.

Electron Sea model

Metals have ability to conduct electricity, ability to conduct heat, formation into sheet drawn, into wires and lustrous appearance. One over simplified model that can account for some of the properties is electron sea model. The metals picture as a network of positive ions immersed in a "sea of electrons". In Lithium  the ions would be Li+ and one electron per atom would be contributed to sea. These free electrons account for the characteristic meal properties. If metals ends are connected to the external source of electric current, one end free electron cross through metal and leave the other end at the same rate in thermal conductivity in electron .

By hammering the internal structure remain unchanged as a sea of electrons rapidly adjust to new situation.

Characteristics of Bond |Bond Length|Bond Enthalpy|Bond Angles

Characteristics of Bond |Bond Length|Bond Enthalpy|Bond Angles

Bond Characteristics

Hello friends welcome to our blog, Today we are going to discuss the various bond characteristics.we know that the chemical bond is possible only if atoms will acquire minimum energy and maximum stability. If it is not having minimum energy than the bond will be very much unstable.

Bond length 

Bond length may be defined as:
                 The average equilibrium distance between the centres of two bonded atoms.

It is also called as Bond distance. The bond length of different covalent bonds are determined by X-Ray diffraction methods.
For covalent bond, It is sum of covalent radii of bonding atoms.For example, Bond length of C-CL bond is cl +  c.
The value of Bond length is expressed in picometre(1 pm=10  -12metre). The various factors such as resonance, electronegativity,hybridization,steric effect etc influence the bond length.

Factor Effect Bond length

1. Size of atoms. The bond length is directly linked with the size of bonding atoms.The bond length of Polar bond is smaller than non polar bond length. For example H-Br bond length(141 pm) is more than H-Cl Bond (127 pm)

2.Multiplicity of bond. The length of double bond(C=C) is less than the length of single bond(C-C) between the same atoms(homo atomic) and the triple bonds(C≡C) even shorter than double bond .

Triple Bond<Double Bond<Single Bond

C≡C            <   C=C               <    C-C

The Multiplicity of the bonds between two atoms brings them close to each other. As a result, the bond length decreases. For example, bond length of C-C bond is 154 pm and the value of C=C bond is 134 pm.

3.Type of hybridisation. The value of  bond length is also influenced by the type of  hybridization.Since s orbital is smaller in size as compared to p orbital,Therefore,greater the s- character smaller will be the bond length.
Example: The alkanes (C-C) have 25% of s character.33.3%  s character  in alkenes(C=C) and
50% as character in alkynes (C≡C).
                   


4.The bond length of same type of two atoms diatomic molecules are twice the covalent radius.

Bond length table

                     Bond Length of Some Common Bonds








Bond Enthalpy

When atoms combine to form bond a certain amount of energy is released.Same amount of energy is needed to break Bond into atoms.Bond enthalpy or bond energy may be defined as

the amount of energy required to break one mole of bond of a particular type in between the atoms in gaseous state of a substance.

Factor Effect Bond Enthalpy

1.The magnitude of bond energy depends upon the type of bonding. Most of the covalent bonds have energy between 50 to 100 kcal per mole.The strength of sigma bond is more than than that of pi bond.

2. If a molecule contains more than one bond of same type, then their bond enthalpy are not same because of the presence of different neighbouring atoms. In such cases, bond enthalpy is the average of bond enthapies of all these bonds.
For example, Cl-Cl Bond enthalpy is 239 kJ per mole while H-H  bond is 433 kJ per mole.

3.If a diatomic molecule contains triple C≡C bond,then it has higher bond energy than that of double bond.Similarly,double bond carbon atoms has higher bond enthalpy than single Bond between the same atoms.

Order

C≡C           >   C=C             >    C-C

4. The bond energy is depend upon the bond length.Shorter the bond length higher is the bond energy

5. The bond energy decreases with the increase in lone pair(lp) on bonded atoms.Electrostatic repulsion of lone pair electrons with  the bonded atoms.

Lp-Lp>Lp-Bp>Bp-Bp

6.Bond energy is also affected by the resonance structured.
Resonance structure. It is a phenomenon of which a molecule expressed in different forms none of which can explain all the properties of molecules.

7.In case of similar molecules bond energy decreases down the group

8. In hybridization the order of energy is

Sp3>sp2>sp>p>s


C H bond energy

The bond dissociation energy of all C-H bonds in methane is not same. Actually when one C-H bond breaks away the electron environment for the remaining C-H Bond change. The carbon atom is now linked with the three C-H bond and not four. Therefore bond dissociation energy changes.

CO bond Energy

The carbon oxygen bond is strongly polarized towards oxygen beacuse  oxygen has much higher electronegative value  than that of carbon.Therefore, the bond length between carbon and oxygen shortens and hence cause the greater bond energy.Bond energy is increasing when going from single to double(CO2) to triple bond(CO)

Bond Angles

Angle between the two adjacent bond of an atom in a molecule made up of three or more atoms is known as bond angle. Bond angle mainly depends upon three factors.

1.Electronegativity. If the central atom is not high electronegative then, bond angle decreases.


2.lone pair repulsive.Lone pair plays a major role in changing the bond angle. If central atom is having lone pair of electrons then the central atom lone pair try to repel the share pair(bonded atoms) of electrons.This is how bonds are slightly displaced inside result in a decrease of bond angle.

3.Hybridization. Bond angle depends upon the state of hybridisation. If the central atom S character increases the hybrid Bond the bond angle increases.


Chemistry Chemical Bond|Types of bonds chemistry

Chemistry Chemical Bond|Types of bonds chemistry


Chemical Bond

Hello friends welcome to blog, Today we are going to discuss chemical bonding.Whenever word bond to hear it means  tie something together and chemical means that is irreversible by physical means.

                       


How are Chemical Bond Form and Defination


Normally,if atom does not complete its valance shell we call  atom is does not exist independently,To exist independently chemical Bond are formed by a force that hold together the different atoms in a molecule is called as chemical bond and number of valence electron(outermost electrons in a shell) participate decide the shape structure and characteristics of a molecule.

Atoms Form Bond To 

Atoms combine to form bond to achieve minimum energy and maximum stability. These are the two key factors that tells why atoms combine to form chemical bond.If atom does not have minimum energy then it will never have stability so bond is not possible.

How do Bond Form

Bond form with stability.Stability means atoms of different elements take part in chemical bond or bond formation in order to complete the octet (outermost shell)and have the electronic configuration of nearest noble gas atoms

Remember

The stability of noble gas elements is due to the presence of 8 electrons in the valence shell(except Helium has duplet) or due to the presence of complete octet.


How do Molecules Bond(Chemical Bond Form)

In the formation of molecule bond only the electrons present in outermost energy shell (valence shell of atom) normally participate while the electrons belong to inner  energy shell are mostly not involved in the Bond formation.we all know that except noble gas elements, the atoms of no other element exist independently. However, a group of atoms known as molecules have independent existence. The formation of chemical bond a molecule will only be formed if it is more stable and has lower energy then individual atoms.. Lewis introduced symbol to represent the valence electrons in the atoms. these are called as lewis symbol in which valence electrons are shown as dotted surrounding the symbol of an atom for example the symbol of carbon  is C while is symbol is

In the light of octet rule, Lewis and kossel have electronic theory of chemical bonding to represent dot structure.




Types of Chemical Bonding(Bond Types)

While talking about this chemical bonding.This question arises itself.

A.By Electron Transfer:- 

                  There is a transference of one or more electrons from one atom to other and the bond         formed is known as ionic or electrovalent bond.

B. By Electron Sharing :-

                  In this case combining atoms mutually contribute one.two,three electrons depending upon their requirement the bond formed is called as covalent bond.


C. Dative Bond:-



                    In some cases only one of the bonding atom contribute the electron pair while sharing is done by both called as co-ordinate Bond or dative Bond.

In addition to these in types of chemical bonding, the atoms of metal linked by metallic bond while inter molecular force of attraction arise hydrogen bonding and Van der waal forces for the formation of covalent bond.

The kind of force in chemical bonding decide the physical state, melting and boiling point, electric conductivity, solubility  and other factor influencing the formation of Chemical Bond.


Fact stated by Kossel in relation to chemical bonding

1. In a Periodic Table the higher electronegative element halogen (group number 17) and higher electropositive alkali metal (group number 1) are separated by a noble gas elements  placed on the extreme right in the periodic table .

2. The atoms of elements belongs to halogen family change to negative ion or anion by gain an electron. Similarly,alkali metals family change the positive a cation by lose an electron.

3.Both positive and negative ion acquire noble gas configuration i.e the achieved stable octet by completing its outermost shell

4. The negative and positive is  stabilized by the electrostatic force of attraction which is the experience.

Strongest chemical bond

Strong chemical bonds are the intramolecular forces which hold atoms together in molecules.Strongest chemical bond is sigma bond or Triple bond.

Chemistry Dual Behavior of Matter(de broglie equation)

Chemistry Dual Behavior of Matter(de broglie equation)


Dual Behaviour of Matter

Hello friends welcome to our blog, Today we are going to discuss dual  behaviour of matter. Sir de broglie french physicist gave advance idea by stating that

  A moving particle have dual nature

It means if car is moving in a straight line.It has wave nature and particle nature. However, the wave associate with matter is known as matter wave with characteristics different from the electromagnetic waves. He co-relation the two characteristics in the form of equation known as de broglie equation


lamda(त)=h/mv


Here,wavelength (lamda()) donates the wave nature of moving particle 
While momentum(p=mv) represents the particle nature. 

Momentum and Lamda  both are inversely proportional the Lambda .It means that  

1. Lambda(त) will be maximum(wave character seen) if the mass of the body is  negligible .

2.Similarly, if the object(car) having large mass then it will have wavelength(त) about negligible it means we can not see its the wave character.

3.if object have velocity equal to zero. Then it will lost its wave character because Lambda will automatically becomes zero.


Derivation

According to Planck's theory,
E = hv = hc/
According to Sir Einstein,mass slowly changes to energy when light falls on its as
E=mc2

Comparing both Equation
hc/त=mc2                   
Equating:-
 त=hc/mc
 त=h/mc
त=h/p   (here p=mv)

Relation between Kinetic energy and debroglie

we know,
E=1/2mv2 

multiply both sides with 2m
2mE=1/2mv2 *2m=m2v2

or
mv=(2mE)1/2

According to De Broglie's

Wavelength त=h/mv=h/(2mE)1/2

Chemistry Atomic Radii(atomic radius pm )

Chemistry Atomic Radii(atomic radius pm )

 Atomic Radii

Hello friends welcome to our blog, Today we are going to discuss the atomic radii. The general picture of an atom in our mind is that of sphere. If it is regarded as correct, then it is defined as

the distance from the centre of nucleus to the outermost shell 
containing the electrons.
It is not possible to measure the exact value of atomic radius of an atom of element because atom is very much smaller in size however we can express the different forms of atom depending upon the nature of bonding of atoms these are

1. Covalent radius
2. Van der waal radius
3. Metallic radius

Why not possible to exact determination  of atomic radius is not as Simple?

A. It is not possible to isolate a single atom in order to determine its radius.

B. It is not possible to measure the exact distance of the atom does not have well defined shape or boundary and probability of electron is level zero even at a large distance from the nucleus.

C.The atomic radius is likely to change due to environmental effect. 
                                              and many more reasons

1. Covalent radius 

 In homoatomic molecules (containing same type of atoms) covalent radius is defined as the one half distance between the centres of two bonded atoms joint each other by a single covalent bond. The distance can be measured by the X-ray diffraction and spectroscopic method.Thus

Covalent Radius(Rcovalent)=    Inter nuclear distance in the bonded atoms/(divided)2

Remember 

a.In Hetroatomic atoms covalent radius shifted towards higher electronegative element.

b.If the two atoms linked to each other by a double bond or triple Bond ,then the half of the Inter nuclear distance does  not represent the covalent radius

2. Van der wall radius 

Van der waal radius is the  half the distance between two similar atoms belongs to neighbouring molecule  of the same substance in the solid state.

Actually, the van der waal forces are weak forces their magnitude(power)  of attraction is smaller in gaseous as well as in liquid state of substance. Therefore  radius is determined in the solid state when the magnitude of force is expected to maximum. The value of van der waal radius is more than that of covalent radius. for example the van der waal force of chlorine is 180 pm while covalent radius is 99 pm(pico meter)


3. Metallic radius 

Half the distance between the centre of nuclei of two adjacent atoms in a metallic crystal. Since metallic bond is weaker than covalent bond the inter nuclear molecular distance between the two atoms in metallic bond is more than covalent bond

Remember
Metallic bond is more than covalent bond

When we compare the three atomic radii the order of forces is

Van der Waal radius>Metallic Radius>Covalent radius

 Chemistry Photoelectric effect| Plancks Quantum theory

Chemistry Photoelectric effect| Plancks Quantum theory

Photoelectric effect 

Hello friends welcome to our blog, Today we are going to discuss the photoelectric effect explained by Planck's Quantum theory in 1887. Hertz discovered that

 Whenever a beam of light (made of bundle packets energy called photon) of certain frequency strikes the metal surface the electrons are emitted rejected from the metal surface the phenomena is called Photoelectric effect.


The ejection of electrons from cesium metal is easy because cesium element has tendency to hold the electrons loosely because ionization enthalpy  is very low.

 Ionization enthalpy- Energy required to remove electrom form atom.

                   

How Experiment performed

The whole experiment is carried in a photoelectric cell consists of evacuated glass tube fitted with two electrodes connected to the outer circuit with the voltage battery. The cathode is coated with the metal having low ionization enthalpy (such as Cesium) .Photons of light radiation of certain frequency are allowed to strike on the cathode side. The emitted electron travels towards anode. These are also called as photo electrons because photons are responsible for the emission of electron.

Observation

A. Photon of light of certain minimum frequency called  as threshold frequency.

B. Threshold frequency cause the meeting emission of electron from the metal surface. However photon may have large energy. 

C. The different metals has the different threshold frequency

Explanation

 The photoelectric effect can be explain with the help of particle nature of light which consist of quantum(packet) of photon this was proposed by Sir Einstein. Photon is a source of energy E =h v. Actually the electrons are held by nucleus of the metal atoms by certain force called binding force. In order to  escape electrons we to supply the energy to overcome the binding force. This job is performed by the photon which contains minimum energy be called as threshold energy to break down the binding energy. The threshold energy is also known as work function.

Energy(E=hv)=Work function(hv0)+kinetic energy(1/2m v2)

Remember

1. If the energy of incident Photon is <(less than) threshold energy no electron will be emitted.

2.If the incident Photon has the energy =(equal) to the threshold energy electron will just release from the metal surface

3.In case of incident photon have the energy >(greater than) than threshold energy emit electron will acquire some kinetic energy

4.The kinetic energy of electrons is directly proportional to frequency of striking Photon and 
       it is quite independent of intensity

5.Number of electrons is ejected per second depends upon the intensity of striking Photon
    not upon their frequency












Study of atomic spectrum(spectra levels)

Study of atomic spectrum(spectra levels)


 Study of atomic spectrum 

Hello welcome to our blog,we know electromagnetic spectrum consists of radiation of different wavelength and frequency (VIBGYOR). These are separated and analysed by the instrument called spectroscope. It consists of a Prism  for Dispersion of radiation and also provide the examine of this radiation through spectroscope. However if the telescope is replaced by a photographic film then instrument is known as spectrograph. The pattern of emitted radiation is recorded on a film called spectrum. Different types of radiation emitted are observed depending on the nature is broadly classified into two parts

Absorption and Emission spectra

Emission spectrum 

It is no it is noted used when the radiation emitted from source are passed through prism then received on photographic plate.The radiations may emitted from 

A. Sun, glowing bulb etc.
B. By passing discharge through gas at low pressure 
C. By heating substance to high temperature etc.

The emission spectrum is of two types

i. Continuous spectrum -

 When sunlight light from glowing bulb pass through slit and then through prism it will separate into 7 band of colors from violet to red which is noticed on the photographic plate. These colours are continuous so called as continuous spectrum

Another example of daily life Rainbow which means appears number of times after rainfall during the day time is an example of continuous spectrum .The water droplets present in the sky is small prism when the sun light fall on them it get dispersed into seven colours which appear as rainbow

ii. Line spectrum -

It is notice when the vapours of volatile substance are allowed to fall on Bunsen burner and analyse with the help of spectroscope. Some specific colours appears on photographic plate which are of different for different substances. for example in case of sodium to yellow line having different wavelength and noticed the line is also called as atomic spectrum.which is the actual test identify that no two elements are resemble each other.

Absorption spectrum 

When does sunlight or white light is passed through strike the prism if it appears dark(black) on photographic plate then we called as absorption spectrum otherwise it is continuous spectrum or line spectrum. Dark lines have also same wavelength as of line or continues spectrum.





Atomic Spectrum of hydrogen atom,spectral lines,line spectrum of hydrogen

Atomic Spectrum of hydrogen atom,spectral lines,line spectrum of hydrogen

Atomic Spectrum of hydrogen atom

Hello friends welcome to our blog, Today we are going to discuss explanation of atomic spectrum of hydrogen atom.

During the discovery of structure of atom of various experiments were performed so as to know about the electron proton etc. When the high electric voltage is passed through the hydrogen gas in closed in discharge tube under low pressure it emit  light behind the electrode is analysed by Spectroscope.

Spectroscope 

It is an instrument which is used to analyse radiation of different colour of different wavelength and frequencies.


The Pattern of emitted radiation that is recorded on  film known as Spectrum depending upon the nature of emission and absorbed the spectra is broadly classified into two types

The spectrum consists of large number of lines which are grouped into different series the complete spectrum is known as Hydrogen spectrum. During study various spectral lines were seen of hydrogen spectrum such as lyman, Balmer, paschen, brackett, pfund series .

Rydberg in 1890  gave a simple equation for the calculation of wavelength of different series of hydrogen spectrum.

Explanation  Why See?

According to Bohr theory,We know that electrons are distributed in different energy levels normally electron close to the nucleus as possible( i.e tends to be in lower energy state called ground state) it means when an extra energy is provided to the electron it absorb energy in Quantum(energy packet) and jump to higher energy state called as excited state.

For example- In hydrogen atom only electron is present in k shell and is( n= 1) in the ground state with an energy E1. If it absorb  energy equal to one Quantum (E=hv )it is jump to first excited state with the energy equal to E2. The excited state is unstable the electron will jump back to ground state losing packet of energy as radiation which appears as spectrum which is of different wavelength and different frequency and respond to specific color.

Note :E=hv is (energy absorb by photon)


Lead–acid battery- "Preventive Maintenance, Charging and Equalization"

Lead–acid battery- "Preventive Maintenance, Charging and Equalization"

Preventive Maintenance, Charging and Equalization

Hello friends welcome to our blog, Today we are going to explain that how we can increase the battery life to the maximum with a particular procedure. When metals are exposed to air are kept in open for some time there surfaces are slowly eaten up or corroded. Which is the main purpose that reduces the battery life this is because formation of certain compounds like oxides carbonates sulfides etc. by the gases and water vapour present in air depending upon the nature of metal this results premature battery failure. It may be another reason may be improper charging poor maintenance

To avoid these all situations we need to equalized properly or given a controlled overcharge with the proper interval of time Equalization is one of the most important and must be performed correctly but only as required.

Preventive maintenance

We must aware of acid level when we use cell for the very first time and then we can place on the charging.The reading should be recorded and kept for the life of battery. We must read the specific gravity after we remove from the charging for the first charge.

Remember

A. Record and check the level of electrolyte once a month and equalizer approximately every 4- 5 months.

B. Electrolyte in the lead acid battery is one of the most important component to maximize the life of the battery if we found the level of electrolyte low before battery put into the service we must contact dealer

C. The original acid level of the cell must be maintained back when it below the bottom of the went well (that is tube inside the battery cell with the slot on each side)

D.We never use the tap water also not  contain chlorine because it contains the hardness which causes the reduced in battery life also cause poor battery performance

Recommendation

1.We must keep record the level of electrolyte acid level and equalizing once every 6 months.

2.Specific gravity place an important role to maximize the battery life and reduce over battery maintenance so must record this reading also after every 3 months or 4 months

3.Water level of each cell must be maintained as requirement

4.Generally, cleaning the terminals of batteries are recommended because it plays an important role we can do this by keeping the metal surface smooth by painting it or use of oil or grease.Another method to protect is that use of some least reactive metal which do not get oxidized.

We can also use the solution of baking soda and water used to be neutralized make sure that the vent caps are security tightened and no soda solution get into the battery cell.

State of charge and charging

 The true measure of the battery charge is known by the specific gravity of the battery acid the following shows approximately values at 25 degree Celsius.

Equalization corrective 

It is need to perform if there is a rise of symptoms such as running low capacity of the battery ,will not hold a charge .These kinds of symptoms are of heavily sulfated battery. If it is not being fully charged on regular basis unlimited equalization is performed using the generator sulfation will occur from deficit cycling. 
Sulphate causes resistance to charge and a false high voltage reading will occur the charge controller will helps you to measure false high voltage which further low charging current to set voltage point.
This Further increases under charge condition this is one reason why specific gravity measurement are so important as false high voltage reading can be misleading.You should always confirm at least in the starting that the state of charge by taking specific gravity measurement of one cell when it is fully charged.

Corrective equalization method

The degree of sulfation decides the time to take corrective equalization it is not recommended to equalize with the generator as some generator produce low grade AC.

1.  If you have hydrocaps during equalization 

2. We must set charging controls to high voltage allows by inverter. if the banks are highly sulphated and current is very limited the charge controlled can be removed. Temperature must monitor very very closely.

3. We can also make use of Solar Panel for good dc Source .if grid is not available at high voltages charging with generator can be difficult.

4. We record specific gravity and the temperature of the cell after every 1 hour. if temperature rises to 46(degree Celsius) and reaches to 52(Celsius) remove the battery from charging.

5. If the specific gravity begins to rise the voltage Bank there must be a drop on change on charging current will increase.

6. Check the cell of electrolyte level and add water if necessary

Pulse charging


Pulse Charging has shown that Bank do not get severely sulfated as one with the traditional 3 step charging when subjected to the same under recharge condition. pulse charging reduce the degree of sulfation  but it will not eliminate the need of equalization. 

The benefit of pulse charging is that bank will required less overcharge and less maintenance.

Must Remember

Allow Bank to cool and check the record of specific gravity of each cell

Caution:- if you have hydro cabs you need move during equalization

We can also add  EDTA to increase the solubility of sulfate in an electrolyte.

Chemistry Langmuir adsorption isotherm( Derivation constant)

Chemistry Langmuir adsorption isotherm( Derivation constant)



Langmuir isotherm

Hello friends welcome to our blog, today we are going to discuss Langmuir adsorption isotherm.
We know that pressure and the temperature are the two main factors which can influence(effect) the extent of adsorption of gas on the solid surface. if the temperature is kept constant(same) the amount of gas(x/m) adsorb on the surface of adsorbent and corresponding pressure are known as adsorption isotherms

Remember

1. Reversible Process

To study the effect of pressure on adsorption of gas on the surface of solid we must bear in mind
that adsorption is a reversible process (i.e desorption also taking place simultaneously).In case adsorbent and adsorbate are enclosed in closed container stage reached when amount of gas at adsorbedt become equal to amount of gas desorbed we called this stage is equilibrium stage the surface of the adsorbent gets saturated with the adsorbed gas and no more adsorption occur

2. Adsorption isotherm

iso- (means) -same                                therm-(means)- temperature


The main features of adsorption theory are as follow

This theory was studied by a Langmuir in 1916 and a Nobel Prize was awarded to the scientist. The scientist studied the concept of adsorption. Lets see what he found in experiment and relate with the mathematics and drive an expression for this isotherm the main features are
1. The layer of gas absorbs only one molecule thick(i.e unimolecular) in nature since this type of adsorption is noticed only in case of chemisorption
Note- Langmuir adsorption isotherm is applicable only to chemisorption

2. Adsorption process having two opposite tendencies that is condensation(adsorption of gas molecules) on the surface of the solid and evaporation(desorption of these molecules) back to gaseous state

3. The rate of condensation of gas is proportional to uncovered surface of adsorbent while that of evaporation to its covered surface


Derivation


To start with the entire surface of solid is uncovered and the rate of condensation is very high while that of evaporation is negligible with the passage of time more and more surface becomes covered as a result rate of condensation decreases while evaporation increases when the two are equal.

Suppose  a one centimeter of surface of solid exposed to gas maintaining pressure p. Let at any time the surface covered by the adsorbate molecules (theta) square centimeter therefore uncovered surface of adsorbent will be (1 - theta) square centimeter



Graph

A graph between log (x/m) and log C is a straight line for small ranges of concentrations.
The values of constants “a” and “b” depends upon the nature of adsorbate, nature of solid
adsorbent, and temperature. “p” is equilibrium pressure



limitations


Lagmuir theory has limitations. This theory of unimolecular adsorption is valid only at low pressure and high temperature. As the pressure is increases or temperature is lowered, additional layer starts forming . This leads to multilayer adsorption.






Chemistry colloidal, suspension,true, solution, Examples, Comparison, particle,size, homogeneous, hetrogeneous,

Chemistry colloidal, suspension,true, solution, Examples, Comparison, particle,size, homogeneous, hetrogeneous,

Colloidal,True and Suspension



Hello friends welcome to our blog, Today we are talking about the colloidal,true and suspension particles.
We know that quantity of substance in excess be called as solvent while substance
which is in small quantity we called as solute.

for example - water as solvent and sugar as solute when we dissolve solute in solvent and solution is prepared

Both solute and solvent are made up of number of particles(mixture). When we dissolve solute in solvent depending upon the solvent solute particle size varies.

Actually there are three types of solution of substance based upon the size of particles these are

1. True solution(homogeneous)2. Suspension Solution(hetrogeneous) and3. Colloidal Solutions( homogeneous) 



True solution-

(example is sugar in water or sodium chloride in water).
The particles of solute are invisible. even we cannot see under under microscope.
The particles of solute pass through ordinary filter also Ultra filter(means animal membrane.) Their appearance is transparent.The particles do not settle at the bottom of the beaker .They may or may not show Brownian motion .


The size of particle is less than 10- 9 meters.


Brownian motion:- zig zag path of particles of solute in solvent
Ultra filter:- advanced filter method
Tyndall effect:- scattering of light when light pass through solution


Suspension solution-

(example sand in water)
These are large in soluble particles. The sand particles which of solute can be seen by naked eye. The particles of suspension neither passed through ordinary filter paper nor animal membrane. They show Tyndall effect .They may show Brownian motion . Particles settle at the bottom of the beaker due to Gravity


The size of particle is more than 10-6 metre.


Colloidal solution -

(soap in water)

These contains the particles having medium size that is lies between true and suspension solution.Soap in water acting as solute. Such particles cannot seen with the naked eye. However light reflected by them can be seen. Under microscope the particles pass through ordinary filter but not through animal membrane. They show Tyndall effect. Particles of solute show Brownian motion. We settle only on centrifugation.


The size of particle lies between 10 -9 to 10 -6 metre


centrifugation:- On Fast Rotating solution by machine. heavy particles get aside and lighter particles collect at the center.(cream from milk)

Interesting facts

1. If we dissolve soap in water it will behave like colloidal solution where is if we dissolve soap in alcohol it will behave like true solution.

2. Another example is when we dissolve NaCl in water solution it will behave as true solution while in Benzene it will behave as colloidal