Chemical Formulae and Names 1

Valence electrons

Electrons in the outermost shell of an atom.

Noble gases

Elements in group 18 (He, Ne, Ar, …). When other elements form ions or molecules, they prefer to end up with the same number of valence electrons as noble gases.

Duplet rule

When forming ions or molecules, small elements like H and Li tend to end up with 2 valence electrons, like He has. (Note: H can also lose an electron to form H⁺, which has 0 valence electrons.)

Octet rule

When forming ions or molecules, most elements tend to end up with 8 valence electrons, like Ne and Ar have.

Na (Group 1) forms what ion?

It loses one valence electron to form a 1+ ion, which has 8 valence electrons, like Ne.

Mg (Group 2) forms what ion?

It loses two valence electrons to form a 2+ ion, which has 8 valence electrons, like Ne.

Al (Group 13) forms what ion?

It loses three valence electrons to form a 3+ ion, which has 8 valence electrons, like Ne.

O (Group 16) forms what ion?

It gains two valence electrons to form a 2- ion, which has 8 valence electrons, like Ne.

Cl (Group 17) forms what ion?

It gains one valence electron to form a 1- ion, which has 8 valence electrons, like Ne.

Formula of an ionic compound

Make sure the total charge is 0. For example, the compound formed between Al³⁺ and O^2- is Al₂O₃. (2 Al³⁺ ions carry a charge of 6+, while 3 O^2- carry a charge of 6-, cancelling out.)

Name of ionic compound

<Name of cation> <Name of anion>

Name of metal cation

Same as name of the metal. E.g., Na is known as sodium, so Na⁺ is known as the sodium ion.

Name of nonmetal anion

Name of the nonmetal but with the -ide suffix. E.g., Cl is known as chlorine, so Cl^- is the chloride anion.

Name for NaCl

Sodium chloride

Formula for magnesium chloride

MgCl₂

Polyatomic ion

An ion containing more than one atom. Examples: NH₄⁺, OH^-, CO₃^2-, SO₄^2-, NO₃^-. (Within the ion, the atoms are connected by covalent bonds.)

Name for NH₄⁺

Ammonium ion

Name for OH^-

Hydroxide ion

Name for CO₃^2-

Carbonate ion

Name for NO₃^-

Nitrate ion

Name for SO₄^2-

Sulfate ion

Name for Na₂CO₃

Sodium carbonate

Name for NaOH

Sodium hydroxide

Formula for sodium sulfate

Na₂SO₄

Formula for magnesium carbonate

MgCO₃

Formula for aluminum hydroxide

Al(OH)₃

Name for CO₂

Carbon dioxide (‘di’ means ‘two’)

Name for CO

Carbon monoxide (‘mono’ means ‘one’)

Common name for H₂O

Water

Common name for NH₃

Ammonia