January 17, 2022
Periodicity
In I/GCSE Chemistry, regular periodic variation of properties of element with atomic number and position in Periodic Table.
Trends across period 3 and its physical properties
1)ATOMIC RADIUS: DECREASES
- Increased nuclear charge pulls electrons towards it
- Same number of inner shells and so electron shielding hardly changes
- Electrons are filling same shell, so nuclear attraction draws outer shell inwards slightly
2) 1st IONISATION ENERGY: INCREASES
- Number of protons increases, so there’s more nuclear attraction acting on electrons
- More energy is needed to remove an electron
Excepts:
- Mg → Al- there’s a decrease (removing electron from a higher energy sub level)
- P → S- Increases distance of outermost shell from nucleus
- Increased electrons shielding of outermost shell by inner shells
3)ELECTRONEGATIVITY: INCREASES
- The larger the atomic number, the more electronegative the atom is
- Increase in nuclear charge
- Bonding pairs of electrons will be found closer to atom’s nucleus
- Atoms attract bonding pairs of electrons MORE strongly
4)ELECTRICAL CONDUCTIVITY:
- Na (1s2 2s2 2p6 3s1) = 1 d.e per atom
- Mg (1s2 2s2 2p6 3s2) = 2 d.e per atom
- l (1s2 2s2 2p6 3s2 3p1) = 3 d.e per atom
Aluminium is a BETTER conductor as it has MORE electrons in its delocalised sea
P, S, Cl, Ar- are NON-METALS and have NO ABILITY to delocalise electrons. They can’t conduct electricity under any circumstances. Silicon is a METALLOID- a semi-conductor
5) MELTING + BOILING POINT: INCREASES
Region 1: Na → Al (metals)
- More delocalised electrons
- Stronger metallic bonding
Region 2: Si (giant covalent structure)
- Strong covalent bonds needed to be broken down
- Requires lots of energy to do this
Region 3: P, S, Cl (non=polar molecules)
- Weak VDW forces holding molecules together
- S has larger molecules with more electrons than P
Region 4: Ar (noble gas- thonoatomic)
- VDW forces between atoms are small
That's all~