PERIODICITY
Classification of elements in s, p and d blocks
• Elements are classified as s, p or d block, according to which orbitals the highest energy electrons are in.
s
block
p
block
d
block
1) In which block are the following elements classified?
Element
C
Mg
He
Rb
Mo
Te
Fe
Cr
P
H
Cl
Block
2) a) Give the electron configuration of silicon. .
b) In which block is silicon classified? ....
c) Why is silicon classified in this block? ...
3) a) Give the electron configuration of vanadium. ..
b) In which block is vanadium classified? 
..
..
c) Why is vanadium classified in this block? ....
Trends across Period 3
Periodicity = pattern in properties across a row which is repeated in each row
0.16
atomic radius (nm)
a) Atomic radius
0.14
0.12
0.1
0.08
0.06
0.04
0.02
0
Na
Mg
Al
Si
P
S
Cl
Ar
increase in nuclear charge —> more protons, with valence electrons in the same shell
shielding remains similar —> negligible increase coming from subshell charge
distance stays same —> valence electrons in same principle energy level
so greater electrostatic force of attraction pulling shell closer to nucleus
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3-July-2015
Chemsheets AS 1056
Enthalpy change to remove one electron from each atom in a
mole of gaseous atoms.
General trend:
1st ionisation energy (kJ/mol)
b) 1st ionisation energy
1600
1400
1200
1000
800
600
400
200
0
Na
Group 2→3 dip:
Mg
Al
Si
P
S
Cl
Ar
Al
Si
P
S
Cl
Ar
Group 5→6 dip:
c) Electronegativity
Power of an atom to attract the two electrons in a covalent
bond.
electronegativity
3
2.5
2
1.5
1
0.5
0
d) Melting and boiling point
Melting and boiling
points (K)
Na
Mg
3500
3000
2500
2000
1500
1000
500
0
Na
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3-July-2015
Mg
Al
Si
P
S
Cl
Ar
Chemsheets AS 1056