Chemical Compounds

Formulae, names, and moles

Learning objectives

Write and interpret chemical formulae for

substances

Distinguish between ionic and covalent

compounds

Write names for simple compounds

Define the “mole”

Use mole concept to determine number of

particles

Calculate molar mass of compounds

Most substances are compounds

Two or more elements combined

Constant Composition: Compound always

contains same amount of each element

Chemical formula tells us the number of atoms of each element Water is H2O

Salt is NaCl

Glucose is C6H12O6

Distinguish between:

Ionic and covalent (molecular)

Ionic (sodium chloride) contain ions

Charged particles

Electron transfer

Solutions conduct electricity (electrolytes)

Covalent (sugar) contain molecules

No charged particles

Atoms share electrons

Solutions don’t conduct electricity

Chemical formula: the use of

subscripts

Ionic compound doesn’t contain molecules Formula tells us simplest

whole number ratio of elements

• NaCl (Na:Cl = 1:1)

• CaCl2 (Ca:Cl = 1:2)

Covalent compound: Formula tells us number of

atoms in molecule

Not necessarily simplest

• C12H22O11 – 12 C atoms, 22H atoms, 11 O atoms

• C6H12O6 – 6 C atoms, 12 H atoms, 6 O atoms

Formulae and counting atoms

Covalent molecules and molecular

formula

Molecular formula gives

number of atoms in molecule

Benzene is C6H6

Simplest formula is CH

But so is acetylene C2H2

Molecular formula

distinguishes among different

compounds with same

simplest formula

Structure and properties

Naming ionic simple compounds

Simple ionic compounds always contain positive metal ion (cation) and negative nonmetal ion (anion)

Rules for names

Metal goes first, name unchanged

Nonmetal second, name ending → ide

Subscripts are not specified in name• Sodium and chlorine → sodium chloride NaCl

• Potassium and oxygen → potassium oxide K2O

• Calcium and fluorine → calcium fluoride CaF2 (notcalcium difluoride)

Anions and polyatomic ions

Naming covalent compounds

There are no metals in covalent compounds

What determines order of names?

Positions in periodic table decide order In same period: one on left is first (NO2, OF2)

In same group: heavier one first (ClF3, BrCl3)

Rules More “metallic” one first

Less “metallic” one second, end → ide

Subscripts are stated (except if first one is one)• CO2 Carbon dioxide

• N2O Dinitrogen monoxide

• P2O5 Diphosphorous pentoxide

Counting particles: The Mole

The mole is a unit of quantity used in

chemistry to measure the number of atoms

or molecules

DEFINITION:

The number of atoms in exactly 12 g of 12C

A mole of anything always has the same

number of particles: atoms, molecules or

potatoes – 6.02 x 1023 – Avogadro’s number

Calculations with moles and

particles

Number of particles = moles x 6.02 x 1023

Number of moles = 231002.6 x

particles

Weighing molecules and moles

Two scales:

Atomic mass unit scale

The mass of an individual atom or molecule in

atomic mass units (amu)

Molar mass scale

The mass of a mole of atoms or molecules in

grams

Confusing?

The Good News

The mass of a single atom or molecule in amu has

same numerical value as molar mass in grams

The atomic mass of carbon is 12 amu

The molar mass of carbon is 12 g/mol

The same is true for molecules and compounds

The formula mass of H2O is 18 amu (1+1+16)

The molar mass of H2O is 18 g/mol

Calculations with molar mass

Moles =

How many moles are in 13.88 g of lithium if

the atomic mass of Li is 6.94 amu?

2.00

massmolar

mass