Topic 13- Intro to periodicity

Question 1

What is the trend in atomic radius across period 3 elements?

Answer 1

Atomic radius decreased across period 3
- increase in nuclear charge as go across due to more protons
- shielding is similar, electrons gained are added to the same shell
- hence, smaller atomic radius as outermost electron is held closer to the nucleus by greater nuclear charge

Question 2

What’s the trend in first ionisation energy across period 3?

Answer 2

Ionisation energy increases across period 3
- increase in nuclear charge as go across due to more protons
- shielding stays same, electron is removed from same shell
- smaller atomic radius , as outermost electron is held closer to the nucleus by the greater nuclear charge
- 1st ie of elements in group 2,5, and 8 are higher than expected because of repulsion due to pairing of electrons in first orbital.

Question 3

What’s the trend in melting point across period 3?

Answer 3

Melting point increases to Si then decreases.
- Na-Al are metals, the metallic bond increases in strength, as there are more outer shell electrons that can be delocalised, giving a greater attraction between the electrons and cations in metallic structure.
- Si has a giant covalent structure and so has the highest melting point in the period, as a substantial amount of energy is enquired to break the large number of covalent bonds.
- P4, S8 and Cl2 are non metals, they are non-polar, simple covalent molecules with low melting points. S8 has most electrons and so the greatest VDWs, argon is monatomic.