Predicting Products

Diatomic elements

H₂,O₂,F₂,N₂,Br₂,I₂,Cl₂

Rule for diatomic elements

When written alone as an element, they always have a subscript of 2

Memory trick

HOFNBRICL (Haw-fin-brickle)

Cl vs. Cl₂

Cl₂ is the element by itself. Never write just "Cl" alone.

Diatomic in a compound (like NaCl)?

No 2 needed. The 2 only applies when the element is by itself.

Valence electrons

Electrons in the outermost energy level, shown as dots around the symbol

Valence electrons for Group 1, 2

Same as the group number (1 or 2)

Valence electrons for Groups 13-18

Last digit of the group number (13 → 3, 17 → 7, 18 → 8)

Potassium (K) dots

1 dot (Group 1)

Metals vs. nonmetals

Metals lose electrons (positive ions). Nonmetals gain electrons (negative ions).

Group 17 (like Cl)

7 dots, gains 1 electron, charge −1

Predicting a synthesis product

Metal + nonmetal → ionic compound. Criss-cross charges to get the formula.

Predicting a decomposition product

A binary compound breaks into its two elements

Balancing rule

Change coefficients only. Never change subscripts.