3.2.1- periodicity

Question 1

How are elements classified in the periodic table

Answer 1

In S, P, D or F blocks according to which orbital the highest energy electron is in

Question 2

Define periodicity

Answer 2

Patterns in properties across a row which is related in each row

Question 3

Trend in atomic radius across a period

Answer 3

Decreases
Protons increase
Electrons enter the same principle energy level therefore experience same shielding
Therefore greater attraction of nucleus to outermost electron

Question 4

Trend in first ionisation energy across a period

Answer 4

General increase
Protons increase
Electrons enter same principle energy level therefore experience same shielding
Atomic radius decrease so greater attraction to outermost electron

Drop in Mg to Al
Drop in P to S

Question 5

Why in first ionisation is the there a drop from Mg to Al

Answer 5

Electrons in Mg are in s orbital electrons in Al are entering the p orbital
Because P orbital is further away
There is less attraction to nucleus

Question 6

Why in first ionisation energies across a period is there a drop from P to S

Answer 6

In S electrons start to pair up in P orbital

Therefore mutual repulsion therefore less attraction to nucleus

Question 7

Explain trend in electronegativity across a period

Answer 7

General increase
Protons increase
Electrons enter same principle energy level so experience same shielding
Therefore atomic radius decrease
Therefore greater attraction from nucleus on bonding electrons

Question 8

Explain electronegativity trend in periods

Answer 8

Na,Mg,Al
General increase because of metallic bonding therefore delocalised electrons Al has the most
Si to Ar
Non conductors
No delocalised electrons
All electrons involved in bonding or lone pairs

Question 9

Explain trend in melting and boiling point across a period

Answer 9

Na,Mg,Al
-Increases strength of metallic bonding
- larger number of delocalised electrons
- larger charge and smaller ions gives rose to a larger charge density
Si
Increase
Many strong covalent bonds must be broken
P4,S8, Cl2
Decrease
Simple molecular substance
Weak van der waals forces must be broken S8>P4> Cl2
Ar
Monoatomic
Very weak van der waals forces must be broke

Question 10

Why does Si have a high melting point and boiling point

Answer 10

Many strong covalent bond must be broken takes must energy

Question 11

P4,S8 ,Cl2 order of boiling points

Answer 11

Weak van der waals forces must be broken

Question 12

Why does Ar have a low boiling point

Answer 12

Monoatomic

Very weak van der waals forces must be broken