Periodic Trends, Polyatomic Ions, and Transition Metal Charges for Chemistry Midterms

Periodic Table Trends

Predictable based on the element's column; elements want a full valence shell (8 electrons).

Group 1 (Alkali Metals)

Typical Charge: +1; Examples: Li^+, Na^+, K^+, Rb^+.

Group 2 (Alkaline Earth)

Typical Charge: +2; Examples: Be^{2+}, Mg^{2+}, Ca^{2+}, Sr^{2+}, Ba^{2+}.

Group 13

Typical Charge: +3; Examples: Al^{3+}, Ga^{3+}.

Group 14

Charge varies; usually covalent, but Pb and Sn vary.

Group 15

Typical Charge: -3; Example: N^{3-} (Nitride), P^{3-} (Phosphide).

Group 16

Typical Charge: -2; Examples: O^{2-} (Oxide), S^{2-} (Sulfide), Se^{2-}.

Group 17 (Halogens)

Typical Charge: -1; Examples: F^-, Cl^-, Br^-, I^-.

Group 18 (Noble Gases)

Typical Charge: 0; Examples: He, Ne, Ar (They don't like to form ions).

Common Polyatomic Ions

Groups of atoms bonded together that carry a collective charge.

Nitrate

Charge: -1; Formula: NO_3^-.

Nitrite

Charge: -1; Formula: NO_2^-.

Hydroxide

Charge: -1; Formula: OH^-.

Cyanide

Charge: -1; Formula: CN^-.

Permanganate

Charge: -1; Formula: MnO_4^-.

Bicarbonate (Hydrogen Carbonate)

Charge: -1; Formula: HCO_3^-.

Acetate

Charge: -1; Formula: C_2H_3O_2^- (or CH_3COO^-).

Chlorate

Charge: -1; Formula: ClO_3^-.

Perchlorate

Charge: -1; Formula: ClO_4^-.

Sulfate

Charge: -2; Formula: SO_4^{2-}.

Sulfite

Charge: -2; Formula: SO_3^{2-}.

Carbonate

Charge: -2; Formula: CO_3^{2-}.

Phosphate

Charge: -3; Formula: PO_4^{3-}.

Ammonium

Charge: +1; Formula: NH_4^+.

Hydronium

Charge: +1; Formula: H_3O^+.

Transition Metals

Most can have multiple charges; Roman numeral indicates charge.

Iron (Fe)

Common Charges: +2, +3.

Copper (Cu)

Common Charges: +1, +2.

Cobalt (Co)

Common Charges: +2, +3.

Zinc

Always +2.

Silver

Always +1.

Cadmium

Always +2.

Nick the Camel Mnemonic

Mnemonic to remember the number of oxygens and charges for polyatomic ions.