At the molecular level we define
Bonding How atoms are held together
structure How atoms are arranged in space
Evolution of Atomic model
E Rutherford's gold foil experiment with A particles
the
Most of theatom is of empty space
Most condensed and heaviest part of atom is small
point called nucleus at centre of the atom
Did not explain electrons around nucleus
Planck's Quantum energy theory
Energy in a system is not continuous but discrete
where energy can have only certain values
Radiant energy EM waves is only emitted in discrete
packs of energy called quanta
Each of these quanta has an energy of
eE hv
Analysis of emission spectrum of hydrogen
00
we also have Brackett series
5
4 Paschen series
and Pfund series
3
Featimeser IR
2
Lyman
Uv Series
Too
1
, Bohr's planetary model
Electrons move around nucleus in orbits of fixed
radii and energy thus orbits are quantised
Emission or absorption is caused by excite.deectrons
moving back to groundstate
Each orbit has an associated principal quantum
number which only takes whole number values
0cm
Eng constant
nz
rn 9h2
x Did not explain well the spectra of heavier
elementsor electrons fixed orbits and quantised
energy
New quantum numbers I Mi Ms
Principal Quantum number n 1,2 3,4n
Angular Momentum Quantum number L 1 0,1 2 n I
To account for the empirical groups of spectral Lines
fine structure
Energy of the orbit increases with 1
Magnetic Quantum number Mi mi I 0 I
Used to justify further split under external magnetic
field hyperfine contributions
o I sub Level
L O m O
L I mi I 1,0 3 sub levels
1 2 me IZ I 1,0 0 5 sub Levels
, Spin Quantum number Ms Ms I 12
To justify further split attributed to the spin of electron
Only possible values are Iz and 12
orientations of the spins within the orbit
Beyond Bohr's model
Light as wave Disturbance or oscillation that moves
through space transferring energy from
one place to another
1 wavelength distance between two maximas
the intensity
fAmplitude Roefatfdgw.to
V frequency Number of waves passing a
point
in one second
Waves show interference effects
in phase constructive when two waves have the
same sign move to same direction and are super
imposable
Final wave is sum of the two waves
Out of phase destructive when two waves have the
opposite sign but move to same direction
May cancel each other completely
Light as particle Photoelectric effectEjection of electrons
from metallic surface depends on the
frequency of light
If frequency is too low electrons are not ejected no
matter how intense the light is
C f l d
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