Chapter 5Chapter 5Section 3Section 3

Polyatomic Ions

and

Naming Compounds

Formulas for Ionic Compounds

• To write formulas for compounds you must remember that the molecule must be neutral.

1)Hydrogen (H+1)oxidation # is +1 and Oxygen (O-2)is -2

2) you need 2 (+1) to cancel out the – 2

3)So 2 Hydrogens are needed to match every Oxygen. (H2O)

• Criss-Cross Method

Polyatomic IonsPolyatomic Ions• Ions – elements that have

lost/gained electrons

• Anions – ions have gained electrons & are negative(-)

• Ca(+)(+)ion-ions that have lost electrons and are positive (+)

• Polyatomic ions- multiple atoms hooked together that have +/- electrons

Polyatomic Ion Con’tPolyatomic Ion Con’t• Polyatomic ions are covalently bonded atoms that have

either too many electrons between them or not enough and are placed in parentheses to show their charges.

• (OH)- =Hydroxide, (NH4)+ =Ammonium are some examples

• Subscripts

tell # of atoms

• Superscripts tell

# of electrons

gained/lost

Naming Ionic CompoundsNaming Ionic Compounds• Compounds are between Metals & Nonmetals.

• Metals are always listed 1st & retain their name

• Non-metals are always listed 2nd & their ending is changed to “ide”

• Sodium (metal)+ chlorine (nonmetal)= sodium chloride

Naming Covalent CompoundsNaming Covalent Compounds Use Numerical prefixes To:

1) show how many atoms of the first nonmetals there are in the compound

2) on the second non metal

to show how many atoms there are, and change ending to -ide.

• N2O4 = dinitrogen tetraoxideide

TESTTEST

NO Ch. 5 NO Ch. 5 TESTTEST

FRIDAY!!!

TESTTEST

Semester Semester FinalFinal

Thursday-19Thursday-19thth (1 (1stst, 3, 3rdrd, 5, 5thth))

Friday-20Friday-20thth (2 (2ndnd, 4, 4thth, 6, 6thth))