Chapter 6 Chemical Names and

Formulas

Molecules and Molecular Compounds

• Molecule - Basic unit of a compound

• Molecular Compound - a compound that is composed of molecules (two or more nonmetals)

Characteristics of Molecular Compounds

• Representative unit- molecule• Type of elements- nonmetals

ONLY• Physical state- solid, liquid or gas• Melting point- low

Ions and Ionic Compounds

o Ion- atoms or groups of atoms with a charge.

o Ions form when an atom or group of atoms gain or lose electrons

Atom – neutral particle# protons = # electrons

Ion – charged particle (lost or gained electrons)# protons ≠ # electrons

Atom vs. Ion

Charge = # of protons – # of electrons

3 – 3 = 0

This is an

ATOM

neutral

Find the charge…

Sodium Sodium atomatom

Sodium ionSodium ion

Protons: 11Electrons: 11Charge: 0

Protons: 11Electrons: 10Charge: +1

lost 1 electron

protons > electrons = + charge

Chlorine atomChlorine atom Chlorine ionChlorine ion

Protons: 17Electrons: 17Charge: 0

Protons: 17Electrons: 18Charge: -1

gained 1 electron

protons < electrons = – charge

Ions and Ionic Compounds

1. Cation - a positive ion formed when an atom loses electrons.

o A positive ion would have the same name as a normal atom

o BUT… they have the same name, they have different chemical properties

Example- Na and Na+

Sodium Atom Sodium Ion

Ions and Ionic Compounds

2. Anion- a negative ion formed when an atom gains electrons.

oThe name of an anion is changed to -ide

Example: Cl and Cl-

chlorine atom chloride ion

Characteristics of Ionic Compounds

Ionic compound- composed of metals and nonmetals (cations and anions)

• Ionic compounds are electrically neutral•The charges on the anions and cations in the

compound equal zero

• Representative Unit - formula unit• Type of elements – metals and nonmetals• Physical State - solids• Melting Point - high

• Chemical Formula - shows the kinds and numbers of atoms in the smallest representative unit of a substance

Examples: O2, N2

•Molecular Formula - shows the kinds and numbers of atoms in a molecule of a compound. (groups of nonmetals…molecular compounds)

Examples: CO2, H2O

• Formula Unit - lowest whole-number ratio of ions in an ionic compound. (metals and nonmetals…ionic compounds)

Examples: MgCl2, AlCl3

Representing Chemical Compounds

Is the compound ionic or molecular?

1. NaCl2. N2O

3. SO2

4. MgCl25. CCl2

Name each: atom or ion

1. Mg2. Li3. Mg+2

4. Li+1

5. Cl6. Br7. Cl-1

8. Br-1

Ionic Charges:

Ionic Charges

Transition Metals- can have more than one charge, a Roman numeral in parenthesis indicates the numerical value of the charge

Ionic Charges

Exceptions– Ag is always +1– cadmium and zinc are always +2

Practice: What is the charge of each ion typically formed by each element?

1. Sulfur2. Lead, 4 electrons lost3. Strontium4. Argon5. Bromine6. Copper, one electron lost

Need to look at the charges of both ions because the compound must be neutral. (overall charge = 0)

NaP

BrCaO Al

+1

-2 +3

+2 -1

-3

Crisscross the numbers and drop the charges

Na O+1 -2

2

Na2O

Al S+3 -2

2

Al2S3

3

Use parenthesis if you have more than one polyatomic ion (an ion with more than one atom)

Ca NO3

+2 -1

2

Ca(NO3)2

Mg PO4

+2 -3

3

Mg3(PO4)2

( ) 2( )

CO3( )

Reduce the subscripts if possible

Mg O+2 -2

2

MgO

2 Sn+4 -2

2

Sn(CO3)2

42

4. According to the information above, what is the chemical formula for

aluminum sulfate?

a. AlSO4

b. Al2(SO4)3

c. Al3(SO4)2

d. Al6SO4

Al3+ SO42-

5. What type of bond is formed between two potassium atoms and one sulfur atom?

a. Ionic Bondb. Metallic Bondc. Hydrogen Bondd. Covalent Bond