Electronic structure

1
Electronic structure

• Shells
• Sub shells

2
Electron arrangements in atoms

• Also known as Electron configuration
• Electrons exist in energy levels
• any element can be identifies by its
  configuration eg
• Li is 2,1
• Cl is 2,8,7
• Ions can be similarly classified
• O 2- is 2, 8 F- is also 2,8 Na is also 2,8

3
Have a go at identifying the first twenty two
elements and placing them in the periodic table
from their electron configurationCan you beat 1
minute?http//www.activescience-gsk.com/games/pla
y/index.cfm?module5
4
What do you notice about Sc and Ti?

• They have more than eight electrons in shell 3
• They are in the block known as transition metals
• This block is called the d block

5
S block
P block
D block
F block
F block
6
What about these blocks ?

• The electron shell picture is a simple view of
  electron arrangement based on hydrogen
• Hydrogen has only one electron
• Other elements have more electrons
• Their electron shells are split into sub shells
• s, p, d and f relate to sub shells
• each main energy level is given a number, n 1, 2
  or 3

7
Where is their evidence of sub shells

• Emission spectra of elements
• Successive ionisation energies gives evidence of
  arrangement in shells
• First ionisation energy is evidence of the
  existence of sub shells

8
Graph of first ionisation energy vs atomic number
9
Sub shells

• The inner shell n 1 has one sub shell. An s
  sub shell
• The second shell, n2, has two sub shells an s
  and a psub shell
• The third shell, n 3, has 3 sub shells an s,
  a p and a d
• and so on!!!

10
Sub shells are made up of sub sections called
atomic orbitals

• s sub shells can contain up to two electrons in
  one s atomic orbital
• p sub shells can contain up to six electrons in
  three p atomic orbitals
• d sub shells can contain up to ten electrons in
  five d atomic orbitals
• each orbital can contain a maximum of two
  electrons

11
energy
4f
4d
n 4
4p
3d
n3
4s
3p
3s
2p
n2
2s
n1
1s
Shell
Sub shell
12
Rules for filling up atomic orbitals with
electrons

• Electrons always go into the lowest available
  orbital
• Electrons are negatively charged so orbitals are
  occupied singly first
• Electrons repel but they possess a property
  called spin. Electrons spinning in opposite
  directions attract. For electrons to pair up
  they must have oppositely paired spins.12

13
What you must be able to do

• Represent the electron configuration of the
  elements using s,p,d,f notation
• Draw diagrams using the electrons in boxes
  convention for representing electrons in sub
  levels,and orbitals
• Know and be able to explain the order in which
  the sub shells fill

14
1s2 2s2 2p3
This element is ..
N
This letter tells you the subshell
This number tells you the main energy level or
shell
This number tells you the number of electrons in
a sub shell