Chemistry - The Periodic Table: Chemical periodically

Trend of atomic radius

Atomic radius = the distance between the nuclrus and the outermost shell e-. (Distance bw 2 atoms of same elements’ nuclei)/2

• Across the period, there is an increase in e- and protons by 1

• → same shielding effects

• e- are more strongly pulled to the nucleus (higher nuclear charge as protons increase)

—> ATOMIC RADII DECREASES AS GOING ACROSS THE PERIOD 3

Trend of ionic radius

• metals produce cations (+)

• non-metals produce anions (-)

GENERALLY DECREASE across the period due to the increase in nuclear charge, but show a sharp increase between cations and anions.

Going across P3- to Cl-, the radii decreases as the nuclear charge increase across the period and fewer e- is gained by atoms.

Cations have lost their valance e- —→ MUCH SMALLER THAN THEIR PARENTS (as less e- → less shielding)

Across the period, ions get smaller (Na+ → Si 4+) (as the increase of nuclear charge attracting the outer e- in the 2nd principal quantum shell, as there are more nuclear charge while the atoms lose more e-)

Anions are LARGER THAN THEIR PARENT ATOMS (as each atom gained one or more e- in their third quantum shell)

—> increase the repulsion between e- , while the nuclear charge is still the same → e- cloud spread out.

The trend of melting point

A GENERAL INCREASE IN M.P. UP TO SILICON, AFTER SILICON, M.P. DECREASE SIGNIFICANTLY.

• silicon has the highest melting point

• Na, Mg, Al are giant metallic structure with metallic bonding, Their MP increase across the period as the metal-metal bond strength increases bc the charge of the metal ions increase and the atomic radius decreases.

• Silicon is macromolecule wth strong covalent bond → high MP

• P₄, S_8, Cl₂ are all simple covalent molecules. Their M.P are dependent on the strength of their van der Waals’/intermolecular forces. The more atoms in a molecule = stronger focre → Sulfur has the greatest M.P.

Trend in electrical conductivity

ACROSS THE PERIOD, DECREASE SIGNIFICANTLY.

Initially, there is an increase in EC from Na to Al, and then this decreases across the remaining elements.

Conductivity relies on the presence of charged particles (such as ions or electrons) which are free to move

• Metallic compounds can conduct electricity