Atomic structure Flashcards
properties of positive rays
- travel in straight line
- show deflection by electric field & magnetic field, showing they are positively charged
- flash on ZnS plate
- e/m ratio varies with gas
- e/m ratio maximum for hydrogen(lightest gas)
(cathode rays greater than positive rays)
postulates of Quantum theory
- energy is emitted or absorbed in discontinuous manner in the form of energyh packets , quanta. light packets are called photons
- Energy of quantum direct relation with freq(v)
E=hv……h=6.625 x 10-34 Js - v=c/y(wavelength)
[1A(angstrom)=10-10m]
- number of waves per unit length is wave numer
v=1/y
E=hcv-
Bohr’s atomic model
[based on planck’s wuantum theory]
1.e- revolves around nucleus in orbits. each orbit is quantized(has fixed energy)
2.energy of e- fixed in one orbit.
means it neither absorbs or emits energy being in an orbit, [unless when it jumps from an orbit to other]
- change in energy of electron given by
E= E2-E1=hv - mvr=nh/2pi
[where n= 1, 2 , 3….]
total energy of e- in an orbit
E= K.E + P.E
P.E= -Ze2/4piEor
K.e= 1/2 mv2
[energy of bonded e- is negative and free e- is zero]
defects of bohrs atomic model
- failed to explain origin of spectrum
- failed to explain multiple structure of spectral lines
- atomic model is not flat[2D]
- Tony stark effect: splitting of specral line in presence of electric field
type of quantum numbers
- principal (n)
- Azimuthal (l)
- Magnetic (m)
- spin (s)
[1,2,3 derived from schrodingers wave equation]
principal quantum number(n)
represents shells/orbits, showing energy of a shell.
[n=1,2,3,4,5…..n]
{2n^2= max no. of e- in shell}
k shell=2
L shell=8
M shell=18
N shell=32
{n^2= no. of orbitals in a shell}
K=1
L=4
M=9
N=16
Azimuthal quantum number (l)
gives the idea of energy of SUBSHELLS
l=0,1,2,3,4………
l=n-1
applications of azimuthal
- no. of orbitals in a subshell
formula: (2l+1)
l; subshell orbitals
0 s 2(0)+1=1
1 p 2(1)+1=3
2 d 2(2)+1=5
3 f 2(3)+1=7
- the number of e- in a subshell is calculated by;
Formula: 2(2l+1)
s 2[2(0)+1]=2
p 2[2(1)+1]=6
d=10
f=14
magnetic quantum number(m)
m=0, +-1, +-2, +-3 ……
value of m can be calculated by m=+-l (azimuthal)
l subshells m values no.oforbitals
0 s 0 one s-orbital
1 p -1, 0, +1 3 degenerate
2 d -2,-1,0,+1,+2 5 degenerate
3 f -3 ,-2,-1, 0, +1,+2, +3 7 degenerate
spin quantum number(s)
spin of e- in an orbit to satisfy the magnetic moment so as to avoid repulsion with each other.
+1/2 or -1/2
aufbau principle
ground state of an atom or ion, e- fill low energy subshells before occupying higher levels.
increasing order of subshells
1s<2s<3s<3p<4s<3d<4p….
hunds rule
*degenerate orbitals are orbitals with same energy such as px py pz exist in different directions but same energy.
more than one e- available for degenerate orbitals,theyre placed in seperate orbitals with opposite spins.
pauli exclusion principle
an orbital can have max of 2 e- of opposite spins
OR
no two e- in an orbital can have same set of all 4 quantum numbers.
quantum numbers applying formula.
n, L, m, s
e.g: 1s2
n=shell
here, n=1.
L=1-n(principle quantumm number)
L=1-1=0.
m=+-L
m=0.
s=+1/2, -1/2
*spin quantum numbers always different due to opposite spins.
