Topic 3: Periodicity

the repeating pattern of physical and chemical properties shown by different periods in the periodic table

the distance from the centre of the nucleus to the outermost shell of electrons

• across a period (→): ↑ nuclear charge = ↓ radius • because all elements in a period are isoelectronic, but no. of protons ↑ • down a group (↓): ↑ no. of shells = ↑ shielding effect = ↑ radius

• aka covalent radius - half of the distance between the centre of the nuclei of 2 covalently-bonded atoms

• the covalent bond is formed by the overlapping of atomic orbitals • the overlapping region becomes common ground

the effective distance from the nucleus of the ion up to which it has an influence in the ionic bond

• radius of cation < radius of parent atom • as the no. of shells decreased by 1 • radius of anion > radius of parent atom • as anions contain more e-s

Across a period (→): • m.pt depends on the element structure and the type of attractive forces holding atoms together • metals: have metallic bonding, so ↑ no of e-s = ↑ m.pt • metalloids: macromolecular covalent structures with strong bonds = ↑ m.pt • non-metals: simple molecular structures with weak intermolecular forces = ↓ m.pt • noble gases: monatomic molecules = ↓ m.pt Down a group (↓): • Gp 1: ↑ no. of shells = ↑ shielding effect = ↑ radius = ↓ m.pt • Gp. 7: ↑ attractive forces between diatomic molecules = ↑ m.pt

• the amount of energy required - to remove 1 mol of e-s from 1 mol of atoms in gaseous state

• across a period (→): ↑ no. of valence e-s = ↑ no. of protons = ↑ ionisation energy • values don’t increase regularly across a period • due to new sub-levels being filled • and existence of paired electrons (paired e-s have greater repulsion between them so are easier to remove) • down a group (↓): ↑ no. of shells = ↑ distance between nucleus and electron = ↓ ionisation energy

Drop in value between: • Be and B • Mg and Al • N and O • P and S • Be and B, and Mg and Al, due to existence of a new subshell in B and Al • N and O, and P and S, due to the fact that electrons in O and S’s outer orbitals are paired

• amount of energy released when a mole of electrons is added to a mole of gaseous atoms • represents ability of an atom to hold additional e-s • ↑ tendency = ↑ Eea

• nuclear charge: ↑ nuclear charge = ↑ Eea • size of atom: ↑ atomic radius = ↓ Eea • e. config.: stabler configs = ↓ Eea

• across a period (→): ↓ radius and ↑ nuclear charge = ↑ Eea - down a group (↓): ↑ radius and ↑ nuclear charge = but effect of ↑ radius is greater = so ↓ Eea

a measure of the ability of atoms to attract a shared pair of electrons toward itself in a covalent bond

bond in which electrons are shared unequally, resting in a partial polar charge

• across a period (→): ↑ nuclear charge = ↑ electronegativity • down a group (↓): ↑ radius and ↑ nuclear charge = but effect of ↑ radius is greater = so ↓ electronegativity

• acidic oxide • basic oxide • neutral oxide • amphoteric oxide

Down the group: • reactivity increases • m.pt/b.pt increases • density decreases

2M (s) + 2H2O (l) → 2M+ (aq) + 2OH-(aq) + H2(g)

• Li floats and reacts quietly • Na melts in a ball and fizzes rapidly around the surface • K’s reaction is exothermic enough to ignite evolved H

2M (s) + X2 (g) → 2MX (s)

down the group: • m.pt/b.pt increases • density increases • reactivity decreases

• highly reactive • good oxidizing agents • ↑ reactivity = ↑ oxidizing ability