Flashcards

Atomic Structure

Prajjwal Sanskar English 74 cards

Cards in this deck (74)

1Cathode RaysJulius Plucker did an experiment for cathode rays
He conducted electricity of order of
10,000 V or more through a gas a very low pressure (10^-4 atm) and saw some sort of invisible rays from cathode to anode called cathode rays.
2Properties of Cathode raysFollowing are properties of cathode rays
1.Path of travelling is straight from the cathode with a very high velocity as it produces shadow of an object placed in it,s path.
2.Cathode rays produce mechanical effect.If small paddle wheel is placed between the electrodes it rotates.This indicates that the cathodes rays consists of material matter.
3.When electric and magnetic field are applied to the cathode rays ,the rays get deflected establishing that they consist of '-'vely charged particles.
4.Cathode ray
(1)Produce green glow when strike the glass wall beyond anode.Light is emitted when they strike ZnS screen.
(2)Penetrate through Al and metals.
(3)They affect photographic plates.
e- is basic constituent of all matter.
3Specific Chargee/m=1.76*10^11C/kg
It is same for cathode rays irrespective of gas used but not for anode rays.
4Anode raysGoldstien repeated the experiment with perforated walls and found new rays coming out,through hole in the cathode.
Properties
1.Anode rays travel along straight paths because the produce shadow of an object placed in their path.
2.They rotate a paddle wheel placed in thier path.This shows they are made of material matter.
3.They are deflected towards negative plate of electric field indicating they are +vely charged.
4.For different gases the ratio of charge to mass is different for different gases because proton can not be removed from nucleus by passing electricity.Hence,H2 gas has max. specific charge since m is minimum for H2 gas.
p+ is basic constituent of all matter.
5NeutronIt was discovered by Chadwick.
He bombarded thin sheet Beryllium with alpha-particles.reaction took place as follows,
Be + He 2+ = C + n(neutron since it,s mass>proton,s mass)
6Thomson,s Model of an atomNo.of +ve charges=no.of -ve charges
Hence atom is neutral.
It consist of +ve charges on a sphere with -ve charge.
7Rutherford ExperimentObservations
1.Most of the alpha particles passed straight through gold foil without deflection from their original path.
2.Some of them were deflected by small angles while some the were deflected by large angles.
3.A very small percentage(1 in 1 lakh) were deflected through angles ranging from 90 degrees to 180 degrees.
8Rutherford nuclear concept of atom1.The atom of an element consist of +vely
charged nucleus which is situated at centre of the atom,it carries almost entire mass of an atom,its volume is negligibly small as compared to volume of the atom.
2.The electron revolve around the nucleus in different concentric circular paths called orbit in empty space in an atom.Also,number of electrons=no of protons.
9NucleusElectron,protons and neutrons are fundamental particles of all atoms(Except hydrogen)
Electron's Mass=9.11*10^-31 kg
Charge=-1.6*10^-19 C
Discovered by J.J Thomson and Stoney Lorentz
Proton's Mass=1.672*10^-27 kg
Charge=+1.6*10^19
By Goldstien and Rutherford
Neutron's Mass=1.674*10^-27 kg
Charge=0
By James Chadwick
Note R(radius of nucleus)=R naught*A^1/3
1.33*10^-13 cm
(Obtained after Rutherford experiment)
10Uncommon fundamental particlesPositron-Positive Electron,(e+ or 0 e 1)
Discovered by Anderson
It is very unstable and combines with e- to form Gamma rays(energy radiation) by this annihilate each other.
Neutrino-Discovered by Paulling. It has zero charge and zero mass.
Anti neutrino-By Fermi. It has (~)zero mass and zero charge.
But opposite in spin as neutrino.
Mesons-By Yukawa. Mesons may be +vely or -vely or neutral charged particles.
It is responsible for stability of nucleus as by exchange of mesons strongest nuclear force develops which is 10^38 times force of gravity and 10^2 times the electromagnetic force.
mu(+/-),pi(+/-/0),k(+/-/0) are different meson,s.
Their mass is in between proton and electron.
Anti proton-By Segre.Mass equal to proton and charge of electron.
Anti neutron-By Cork.Mass and charge equal to neutron but opposite spin.
11Atomic number and mass numberAtomic no(Z)-No of electron in a neutral atom and no of proton in nucleus.(Proton Number)
Mass no(A)-No of proton and neutron in nucleus called nucleons.
Note-Mass number is not equal to atomic mass as it is average atomic weight =m1x1+m2x2+.../100 or x1+x2+x3...
12Important DefinationsIsotopes
By Soddy
They have same atomic number and chemical properties but different physical properties and atomic mass.
For example,Protium,Deuterium,Tritium etc.
Isobar-The different atoms which have same atomic mass but different atomic number.
Isotone-Elements which have same number of neutrons.
Isoelectronic-The atoms,molecules,ions,or species which have same number of electrons.
Isodiaphers-Elements have same difference between no of Neutrons and Protons.
When a radioactive nucleus radiate
alpha particles the formed daughter(because it can reproduce) nucleus is Isodiapher of parent nucleus.
(formed by removing He 2+ from parent nucleus)
13Some BasicsNuclear Force-Force between two proton,two neutron,a proton and a neutron.
c=f*lambda
Wave length=c/f
1/wave .no=c/f
In an electromagnetic wave,direction of electric and magnetic field are perpendicular.
Wave nature could explain the nature of emission of radiation from hot bodies (black body radiation). Ejection of electrons from metal surface when radiation strikes it(Photoelectric effect)
14Force between two chargesF=k*q1*q2/r^2
k=1/4*pi*epsilon naught=9*10^9 N m^2/C^2
If F is negative it represents attraction
If F is positive it represents repulsion.
15Angular MomentumL=mvr sin(theta)
L=mvr If theta=90 degrees when object is moving in circular about it,s center.
Theta=Angle between v and r
16Energy of photonE=h*nu
E=h*c/lambda
h=6.625*10^-34 J*sec
Quantum-The smallest energy value.
17Potential Energy of systemu(P.E)=k*q1*q2/r
The P.E increases from innermost to outermost shell.
Negative sign here means attraction and positive means repulsion.
18Work doneW=f*d*cos(theta)
Theta=Angle between d and F
19Bohr Model of AtomPostulates
1.When electrons revolve around the nucleus two kinds of forces act on it
(1)Electrostatic force of attraction of the nucleus,which provides centripetal force
F=-k*Ze*e/r^2
(2)Centrifugal Force=ma=mv^2/r
Clearly these two forces balance each other to keep electron moving in these orbits,
mv^2/r=k*Ze*e/r^2
2.Energy of an electron remains constant as long as it stays in same orbit called stationary orbit(Energy levels or main energy levels).
3.When an electron jumps 1 orbit to another it absorbs definite amount and when it comes back it emits energy in the form of electromagnetic radiation.
That is
Change in energy=En2-En1=h*nu
En1=Energy of stationary orbit n1
En2=Energy of stationary orbit n2
4.Out infinite number of orbits that can be created around nucleus there are only some permissible orbits which have angular momentum as an integral multiple of h/2*pi.This is called quantization of angular momentum.
That is,
mvr=n*h/2*pi
It is applicable for single electron atom
20Drawback of Rutherford Model of atomWhen electron revolve around nucleus they radiate energy because electrostatic force is negative due to which electron with less energy will collapse with nucleus by coming closer to it in 10^-8 sec during this period nucleus exerts more and more force because distance between electron and nucleus decreases.
Note that Bohr orbit in question is applicable to all atoms.
21Negative work and positive work conceptPositive work is done when force and displacement direction is same.But negative work is done when force and displacement direction is opposite.
22Radius of orbitr=0.529*n^2/Z*10^-10=r of H1 atom*n^2/Z
r1/r2=n1^2/n2^2*Z2/Z1
23Velocity of electronv=2.18*10^6*Z/n m/sec
v=v h1*Z/n
v1/v2=Z1/Z2*n2/n1
24Energy variation of P.E,K.E and T.EP.E and T.E are greater at infinite distance from nucleus than closer to it
K.E is maximum at inner most orbit and least at infinite distance from nucleus
Always take magnitude in problems related to energy.
25Energy of an electronT.E=-2.18*10^-18*Z^2/n^2 J/atom
=-13.6*Z^2/n^2 eV
T.E=-K.E
P.E=2*T.E
P.E=-2*T.E
26Einstein lawAccording to this law one molecules absorbes one photon.That is,energy per molecule=h*c/λ
27Some important results1/λ 1=1/λ 2+1/λ 3+....+1/λ n
E2-E1>E3-E4>E4-E5>......
28Time period of electron moving in nth Bohr OrbitClearly T=2*pi*r/v
Hence T=1.52*10^-16*n^3/Z^2
T=T of H1*n^3/Z^2
29Frequency of electronf=1/t so taking t=1.52*10^-16*n^3/Z^2
We have,
f=6.6*10^15*Z^2/n^3
30Current possessed by electronI=1.05*10^-3*Z^2/n^3
31Magnetic momentμ=I*A=9.23*10^-24*n Teslas or A*m^2
32Hydrogen spectrumThis is Rydberg formula,
It has been derived by E2-E1
Remember 1/Rh=911.7 Å
Rh=109678cm inverse
33Classification of spectrum emitted by HydrogenAccording to wave length of spectrum emitted by Hydrogen atom,there are six classification as follows,
1.Lyman n1=1 n2=2,3,4,....
All lines belong to ultraviolet region.
2. Balmer series n1=2 n2=3,4,5,...
First four lines belong to visible region.The rest belong to U.V region.
Red------>3---->2-H-Alpha-Red
4------>2-H-Beta-Green
5------>2-H-Gamma-Blue
6------>2-H-delta-Violet
3. Paschen series(Infrared radiation)
n1=3 n2=4,5,6,....
4.Bracket series(I.R)
n1=4 n2=5,6,7,....
5. Pfund series(F.I.R)
n1=5 n2=6,7,8,....
6. Humphry series(F.F.I.R)
n1=6 n2=7,8,9,....
34States and different types of energies in single electron speciesGround state- n=1
Excited state-n>1
Excitation energy-Energy required to excite an electron from it,s ground state to any excited state.(1>)
Be careful of the word excite.
Binding energy or separation energy-It is the energy required to remove electron from n>1.
Ionization Energy-Energy required to remove an electron from it,s ground state.
35SpectroscopySpectroscope:-It is an instrument used to separate the radiation of different wavelengths.
Pattern of the emergent radiation on screen is called spectrum or spectrogram.
The branch of science dealing with the study of spectra is called spectroscopy.
36Different types of spectra Emission spectra Which is spectrum obtained by emission of photon that carry energy equals to difference in energy levels.Continuous spectra-The spectrum obtained by white light from any source or spectra having no dark spaces.
Line spectra-The spectrum obtained by gas at low pressure in a discharge tube of some volatile salt (e.g of NaCl) placed in Bunsen Burner.In this lines of spectrum are separated by dark spaces.
Continous and lines line spectra are emission spectra.
Absorption Spectra-Absorption by atom result in absorption spectra.
Band spectrum-By molecules.
Both these have lines that separated by dark spaces.
37Fine spectrumIt is the spectrum having two closely spaced lines.
The emission happens at different times by different sub-shells.
This was limitation of Bohr model of atom.
This was Sommerfeld experiment.
38Shape of subshellsIt is like an ellipse.
major axis=n
minor axis=k
n/k=1/1 then it is circular and s subshells
n/k=2/1,2/2
then 2/1 is ellipse ,p subshell where as 2/2 is circular,s subshell.
39Zeeman and Stark effectThis was limitation of Bohr model of atom.
In single electron species s,p,d,f etc sub shell have same energy.
Zeeman effect-Splitting of spectrum lines in the presence of magnetic field.
Stark effect-Splitting of spectrum lines in the presence of electric field.
Zeeman and stark effect confirmed the presence of sub energy levels in subshells also known as orbitals.In the absence of magnetic and electric, they have same energy levels also known as degeneracy
40Shape of Orbitals
41De broglie concept of matter waveMatter has a path like wave when it is in motion(high velocity).
λ=h/p=h/m*v=h/√ 2*m*K.E
This was limitation of Bohr model of atom.
It suggest the daul nature of particle and wave of electron and other objects.
42Wavelenght of electron,proton and alpha particleFor e- λ=12.3/√V
For p+ λ=0.286/√V
For alpha particle λ=0.101/√V
Take care of the word proton,electron and alpha particle.
43Important formulas2πr=n*λ
K.E=qV of particle kept in discharge tube.
44Heisenberg Uncertainty PrincipleIt is impossible to measure position and momentum of electron at any given time.
It applies to all objects in universe.
45FormulaΔx*Δv> or equal to h/4*π*m
ΔE*Δt> or equal to h/4*π
Clearly if Δx=0 then Δp=infinity
For circular motion,
Δ θ*Δω> or equal to h/4*π*m
46Electron during collision with photon
47Schrodinger Wave equationSince we cannot talk of momentum and position of electron we need to have a probability approach for locating an electron in atom.
Schrodinger developed an equation to find out the position of an electron in an atom.
48—On solving this equation we get infinite number of solutions.
But only those value of Ψ will be taken which are
1.Finite
2.Single valued function
3. Continuous
∞
4.∫Ψ^2 dx dy dz=1
-∞
This is f(x)'s probability of finding electron in an atom.
1 means electron is definitely around nucleus.
49Formula Ψ =Ψ(r)*Ψ(theta) Ψ(r)=n,l Ψ(theta)=l,mΨ(r)/r graph for 1s touches x axis at 1-1=0 point
Ψ^2(r)/r graph for 1s touches x axis at
1-1=0
P(r)=Ψ^2 dv /r graph(radial probability distribution curve) for 1s it touches x axis at only one point and it,s maximum probability is 0.529 Å with height of graph decreasing
50Energy absorbed by moleculeIf energy is absorbed by molecule then resultant atoms have equal energy
The energy between atoms of molecule is called bond energy or energy required to break bond.
E per atom=E (absorbed)-E (bond)/N
N=No of resultant atoms
Note-1 cal=4.12J
51Ψ^2-Probable density It is the probability of finding electron in unit volume. Ψ-Amplitude functionHere if dr is the difference between radius of these 2 spheres,then,
dv(Volume)=
4*π*r^2*dr
P(r)=
Ψ^2*4*π*r^2*dr
52NodeIt is the space around the nucleus where the probability of finding electron is 0.
Radial node=n-l-1
Angular node=l
Total node=n-1
Total node including at infinity=n
n=Principal quantum number
l=Azimuthal quantum number
l=0(s),1(p),2(d),3(f),.....
53The wave function of Ψ for s sub shell does not include any function of θ or Ф function Means that it does not include trigonometric function.One finger method-It is a short cut method to multiply or divide numbers with same number of decimal places.
54Proof that electron can not exist in nucleusΔx*Δv=h/4*π*m
Putting electron,s mass and radius of nucleus as error in position,
Hence,Δv=5.77*10^10 m/s
This value shows that error in velocity is very high.So,electron cannot exist in nucleus.
55Shapes of s orbitalsHere,there is no nodal plane but radial node increases for 1st to nth orbit.
Angular nodes is always zero.
56Graph for 2p,3p, etcGraph for s orbitals for Radial probability distribution curve touches 1 times for 2p,2 times for 3p and so on with height of graph almost same but decreasing or increasing.
57Shape of P orbitalsThey are elliptical with radial node increasing with increase in orbit number,the have one nodal plane each,angular node is 1,on positive axis they are positive where as on negative axis they are negative.
58Graph for 3d,4d etcThe graph at first strongly touches x axis then for 3d it touches x axis 1 time ,then for 4d it touches x axis 2 times and so on.
59Non axial d orbitals and axial d orbitalsThe non axial d orbitals are called t 2g orbitals ,whereas,the axial orbitals are called e g orbitals
60Non axial orbitalsIn these orbitals radial node increases with increase in orbit number,angular node is 2,there are two nodal planes.In 1 and 3 quadrant their polarity is positive,whereas it is negative for other quadrants.
61eg orbitalsdx^2-y^2-No of angular node is 2.Nodal plane is inclined 45 and 135 degrees to the axis.
d z^2-They do not have nodal plane but they have nodal surface.No of angular node is 2.
62Quantum numbersQuantum numbers are used to define quantum state of an electron.
Principal quantum number(n)
n=1(K),2(L),3(M),4(N),5...
It was proposed by Bohr.
It gives the size of electron wave,and energy of electron in a given shell.
It gives angular momentum for electron.
n^2=Total number of orbitals in any given n shell.
2*n^2=Total number of electrons in any given shell
63Azimuthal quantum numberIt was given by Sommerfeld.
For any given n shell,l=0,1,2,3,.....,n-1
l=0 -s(Sharp) sub shell
l=1 -p(Principal) sub shell
l=2 -d(diffused) subshell
l=3 -f(fundamental) sub shell
l=4 -g(generalised) sub shell
It gives the shape of electron cloud and number of orbitals in a given shell.
No of orbitals in a sub shell=2*l+1
Max no of electron in a sub shell=4*l+2
Orbital angular momentum=√l(l+1)*h/2π
=√l(l+1)*ħ(h bar)
64Magnetic quantum numberIt was given by Linde.
It gives us idea of orientation of a sub shell in space.
It tells us about the possible orbitals in a given subshell.
m=-l.....0.....+l
For p subshell,Px/Py=+1/-1
Pz=0
For d subshell,d z^2=0
Note-All l,m,n are the roots of shrodinger wave equation.
65Spin quantum number(s)It was given by Samuel Goldsmith and Uhlenbeck
s=+1/2(Clockwise)/-1/2(Anti-clockwise)
It gives direction of spin of an electron.
2 electrons in the same orbitals differ by their spin quantum number.
Total spin(s)=n/2
n=Number of unpaired electrons
in an atom.
Spin magnetic moment(μ)=√s(s+1)*eh/2πmc
or√n(n+2)*B.M
B.M=Bohr Magnetron=eh/4πmc
Spin multiplicity=2s+1=n+1
66Pauli,s Exclusion PrincipleIt was given by Wolfgang Pauli.
No 2 electrons in an can have same 4 quantum numbers because of this principle an orbital can accomodate maximum two electrons with opposite otherwise they will have same quantum number and will disobey Pauli,s principle.
67Hund,s Principle of maximum multiplicityElectron are filled in degenerate energy levels in such a way that each orbitals should half filled with electron with parallel spin then other electron should be accomodated. This done so that there is stability in a atom as electron will move by more distance and will lose energy to make atom stable.
In case of Cu and Cr the electron shift from 4s to 3d so that there stability by more lose of energy.
68Aufbau PrincipleAufbau comes form the German word 'To build up'.
Electron are filled in orbital in such a way that there is increasing order of energy in orbitals.We can find energy of electron by n+l rule if there same value for n+l then the orbital with greater n has more energy.
Here, each line means orbitals passing through these lines has same value of n+l.
69Important unitFeet=12 inches
1 feet=30.48 cm
1 mile=1609.34 m
1 pound=453.6 kg
70Photoelectric effectIt was given by Albert Einstein for which he was given Noble Prize.It proved particle nature of light.
According to Einstein,
E=Ф+K.E(Max)
Ф=Work function
E=Energy of incident photon
K.E(Max)=Kinetic energy of ejected electron
v(Max)=√2h(ν-ν(naught)/m
Among alkali metals and alkaline earth metals the threshold frequency(ν naught) is less than other metals.
The work function decreases down down a group.
Work function-It is the minimum energy required for ejection of electron.
71Saturation Current and intensity of lightIt is the current by ejection of electrons which can not be further increased by increasing frequency and intensity of light.Intensity of light or brightness increases by increasing number of photons per unit time.
72Cases for energy of incident lightIf incident light has more energy electrons will get ejected,if it is equal to work function electron will get removed and will fall and if incident light energy is less than work function nothing will happen.
Also,λ <λ (naught)
73Concept of Photoelectric effectIf intensity of light and frequency of light increases the electrons ejected would increase or energy of electron would increase,which increases photoelectric current but since K.E of electron goes into air resistance,friction etc. and there are limited no of electrons on a particular metal surface current can,t be increased upto a certain limit.
74Millikan oil drop experimentIt was used to measure charge of an electron actually it showed that charge is in integral
multiple on an object.That is,q=n*e