Chemical Names andFormulas

Ch. 6

Introduction to Chemical Bonding

6-1

Molecules

• Molecule = two or more nonmetal atoms that act as a unit– Ex: O2, CO, H2O

• Diatomic Molecules = elements whose natural state has two identical elements– Ex: H2, N2, O2, F2,

Cl2, Br2, I2

Molecular Compounds

• Molecular Compound = compound composed of molecules

• Most composed of 2 or more nonmetals

• Low melting + boiling points

• Most gases or liquids @ room temp.

• Ex: H2O, CO2,

CH4, NH3

Ions

• Ions = atoms or groups of atoms that are charged.

• Forms when atom or group of atoms loses or gains electrons.

– Throws off neutral atom of p+ = e- creating a charge

Cation + Anion• Cation = atom or group of atoms that has a positive

charge.– All metals are cations– Cations lose electrons, becoming positive– Cation name stays the same as element name– Ex: Na+ (sodium), Mg+2 (magnesium), Al+3 (aluminum)

• Anion = atom or group of atoms that has a negative charge.– All nonmetals are anions– Anions gain electrons, becoming negative– Anion name ends in -ide– Ex: Cl- (chloride), O-2 (oxide), N-3 (nitride)

Ionic Compound

• Ionic Compound = compound composed of cations and anions.– Metal cation + nonmetal anion– Are electrically neutral, positive cation balances

out negative anion.– Write the metal first and the nonmetal second.– Ex: NaCl, CaO

• NaCl:

– Na loses 1 electron, becoming Na+ (cation)

– Cl gains 1 electron, becomes Cl- (anion)

Properties of Ionic Compounds• Ionic compounds have different properties from

the properties of elements that make it up.– Solid crystals @ room temp.– High melting point

• Ex: table salt (NaCl) = chlorine (Cl) + sodium (Na)– Chlorine by itself is a fatal green gas– Sodium by itself is explosive when in it comes into

contact with water!– Together they make edible table salt!!

+ =

Comparing Molecular + Ionic Compounds

• Molecular Compound:– Neutral molecule– 2 or more nonmetals

together– Usually liquid or gas– Low melting point

• Ionic Compound:– Made up of 2 or more

charged ions– Neutral compound– Metal + nonmetal– Solid crystal– High melting point

Representing ChemicalCompounds

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Formula’s

• Molecular Formula = represents molecular compounds

– Ex: H2O, CO2, C6H12O6

• Formula Units = represents ionic compounds

– Lowest whole # ratio

– Ex: NaCl, MgCl2, AlCl3

Ionic Charges

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Monatomic Ions• Monatomic Ions = ions consisting of only one atom.• Charges can be determined using the periodic

table!– Group 1: charge is +1– Group 2: charge +2– Group 13: charge +3– Group 14: none – don’t make ions– Group 15: charge -3– Group 16: charge -2– Group 17: charge -1– Group 18: none – don’t make ions

DRAW!Charge: +1 +2 +3 0 -3 -2 -1 0

Transition Element Charges

• Many transition elements (grps. 3-12) have more than one possible charge.– Use roman numerals to differentiate between

them– Iron (Fe): Fe+2 is Iron (II)

Fe+3 is Iron (III)– Copper (Cu): Cu+ is Copper (I)

Cu+2 is Copper (II)• Some transition elements have only one charge.

– Ex: Ag+, Cd+2, Zn+2

See Page 144!

Polyatomic Ions

• Polyatomic Ions = tightly bound group of atoms that behave as a unit and carry a charge.– Ex: SO4

-2, NO2-, HCO3

-

– For naming pairs of polyatomic ions, name according to # of oxygen atoms:• Suffix –ite has one less oxygen then –ate• Ex: SO3

-2 sulfite SO4-2 sulfate

NO2- nitrite NO3

- nitrate

ClO2- chlorite ClO3

- chlorate

See page 147

Ionic Compounds

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Writing Formulas forBinary Ionic Compounds

• Binary compound = compound composed of 2 or more elements.– Must be a neutral compound - positive charge

must balance the negative!– Ex: Na+ + Cl- = NaCl

1 + -1 = 0 – Ex: Ca+2 + F- = CaF2

2 + 2(-1) = 0Confusing?… just cross the charge to become

a subscript! Ca+2 + F-

CaF2

More Examples

• Ex: K + I = ?– What are the

charges?– K+1 and I-1

– 1 + -1 = 0– so… 1 K and 1 I = – KI

• Ex: Li + O = ?– What are the

charges?– Li+1 and O-2

– 1 – 2 = 0– HINT: cross the

charges!– Li+1 and O-2

– Li2O

You Try!

• Write the formula:1. Ca + O

Ca+2 + O-2

2 + -2 = 0 …CaO2. Na + S

Na+1 + S-2

Na2S

3. Al + OAl+3 + O-2

Al2O3

4. B + NB+3 + N-3

+3 + -3 =0…BN

Naming Binary Ionic Compounds

• Write the cation first (+) then anion (-), OR metal first then nonmetal.

• Remember: only anion name changes to suffix –ide!

• Ex: Na+ + Cl- = NaCl

sodium + chlorine = sodium chloride!

Al+3 + F- = AlF3

aluminum + fluorine = aluminum fluoride!

You Try!

• Write the formula and name it:– Li + N

• Li+ + N-3

• Li3N• Lithium nitride

– Mg + Cl• Mg+2 + Cl-

• MgCl2• Magnesium

chloride

• B + O– B+3 + O-2

– B2O3

– Boron oxide• K + I

– K+ + I-

– KI– Potassium iodide

• If transition metals are involved, you need to know which charge is used…– Ex: CoI2 (cobalt could be +2 or +3)

Co? + I- = CoI2

CoI2

Cobalt must be Co+2, so the name is…

Cobalt (II) iodide!

Tertiary Ionic Compounds

• Tertiary Ionic Compounds = compound with 3 different elements.– Usually contain 1 or more polyatomic ions– Ex: calcium + nitrate

Ca+2 + NO3-

Ca(NO3)2Use parenthesis if more

than 1 of polyatomic!

More Examples

• Lithium carbonate

Li+ + CO3-2

Li2CO3

• Potassium sulfate

K+ + SO4-2

K2SO4

• Ammonium sulfite

NH4+ + SO3

-2

(NH4)2SO3

• Chromium (III) nitrite

Cr+3 + NO2-

Cr(NO2)3

Molecular Compoundsand Acids

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Binary Molecular Compounds

• Binary Molecular Compounds = 2 nonmetals.• No charges to balance!• When naming, prefixes are used for both

elements. No mono- on first element!• The second element has the suffix –ide• Write the element that is most left in the table, or

if in the same group closest to the bottom, FIRST

• Ex: N2O – dinitrogen monoxide

PCl3 – phosphorus trichloride

# of Atoms Prefix

1 Mono-

2 Di-

3 Tri-

4 Tetra-

5 Penta-

6 Hexa-

7 Hepta-

8 Octa-

9 Nona-

10 Deca-

You Try!

• Write the name:– OF2

• Oxygen difluoride

– N2O5

• Dinitrogen pentoxide

– Cl2O8

• Dichlorine octoxide

• Write the compound:– Nitrogen trifluoride

• NF3

– Disulfur dichloride• S2Cl2

– Sulfur hexafluoride• SF6

Naming Common Acids

• An acid is a hydrogen ion (H+) and an anion

• Common one’s to know:– Hydrochloric Acid HCl– Sulfuric Acid H2SO4

– Nitric Acid HNO3

– Acetic Acid HC2H3O2

– Phosphoric Acid H3PO4

– Carbonic Acid H2CO3