Topic 3: Periodicity

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

• 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 tendency of similar properties of the element to recur at intervals, if they are arranged in order of increasing atomic number

• across a period, atomic radius decreases due to increased nuclear charge, which pulls electrons closer to the nucleus • down a group, atomic radius increases due to increased no. of shells and increased shielding effect

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

• the amount of energy released when a mole of electrons is added to a mole of gaseous atoms • represents the ability of an atom to hold an additional electron • the higher the tendency, the higher the e.a.

• nuclear charge: higher nuclear charge = higher e.a. • size of atom: the larger the atom, the lower the e.a. • e. config.: stabler configs = lower e.a.

• along a period, e.a. increases, because nuclear charge increases and atomic size decreases • down a group, e.a. decreases, because although size and nuclear charge both increase, effect of increased size is much more pronounced

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

• along a period, electronegativity increases due to increased nuclear charge, resulting in increased attraction between nucleus and electrons • down a group, electronegativity decreases due to increase in atomic size, resulting in reduced attraction

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

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

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

• element whose atom has an incomplete d sub-shell - or can give rise to a cation with an incomplete d sub-shell

PHYSICAL PROPERTIES • high m.pt/b.pt • high tensile strength • high density • malleable and ductile • high thermal & electrical conductivity CHEMICAL PROPERTIES • form compounds with more than one oxidation no • incomplete d-subshell • form complex ions • form colored compounds • act as catalysts when either elements or compounds

Chromium’s config: [Ar] 3d5 • because there’s not much diff between 3d and 4s orbitals • but taking from 3p6 is harder (also because the orbital is full)

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

number of outer shell/valence electrons

number of occupied electron shells

• coz their Mr also increases down the group - thus van der waals/intermolecular forces also increase

• metallic bonding weakens • as radius increases, delocalized electrons are shielded more from the effective nuclear charge through electron shielding effect