COMPOUNDSCOMPOUNDS

CompoundsCompounds

• Pure substances that are made of more than one element are called compounds (molecules)

• Compounds are two or more elements chemically combined.

Examples of compoundsExamples of compounds

SALT: NaCl

SUGAR:C12 H22 O11

WATER: H2O

BREAKING DOWN BREAKING DOWN COMPOUNDSCOMPOUNDS

• Heat can break down compounds.

• Electric energy can break down compounds that cannot be separated using heat

MoleculesMolecules

• Compounds are made of molecules

• Molecules are two or more atoms chemically combined

• Molecules are the smallest particle of a compound that has all the properties of that compound

Two Ways Molecules Form

1. Ionic Bonding - Bonded by electric charge.

2. Covalent - Share outermost electrons.

Chemical Formulas Chemical Formulas • Chemical formulas are

combinations of chemical symbols

• Short way to represent chemical substances

• Most chemical formulas represent compounds

Examples of Chemical FormulasExamples of Chemical Formulas

• Ammonia: NH3

• 1 atom of nitrogen, 3 atoms of hydrogen

• Silver nitrate: AgNO3

• 1 silver, 1 nitrogen, 3 oxygen

• Carbon dioxide: CO2

• 1 carbon, 2 oxygen

Molecules of elementsMolecules of elements• Sometimes

elements are found in nature as molecules–Hydrogen = H2 –Oxygen = O2 –Nitrogen = N2 –Chlorine = Cl2

HH

Drawing chemical equations

Hydrogen

oxygenC C

N N Nitrogen

SubscriptsSubscripts• The small numbers you place to the right of

the symbol.• Must be placed lower

– EX: C2H4O2

– Subscripts apply to what they follow• Gives the number of atoms of the element in

the compound.– 2 carbon, 4 hydrogen, 2 oxygen

• If there is only 1 atom, the subscript is not written.– Example: NaHCO3

Coefficients

• Number placed in front of a molecule or compound.

• Applies to the entire compound.

• Coefficients and Subscripts multiply.

Practice counting atomsPractice counting atoms

• List the elements in each of the following compounds. Calculate how many atoms of each element are present.

1. NaHCO3 4. C6H12O6

2. Mg(OH) 3 5. 2H2O

3. 3H3PO4 6. MgO

Answers to Counting AtomsAnswers to Counting Atoms1. NaHCO3 1 sodium, 1 hydrogen, 1 carbon, 3 oxygen

2. Mg(OH) 3 1 magnesium, 3 oxygen, 3 hydrogen

3. 3H3PO4

9 hydrogen, 12 oxygen3 phosphorous

4.C6H12O6

6 carbon, 12 hydrogen6 oxygen

5. 2H2O4 hydrogen, 2 oxygen6. MgO1 magnesium, 1 oxygen

Chemical EquationsChemical Equations

• Used to describe a chemical process or reaction

• Charcoal burning is a chemical reaction

–1 Carbon atom plus 1 oxygen atom produces carbon dioxide molecules

OR

- C + O2 CO2

oo

Look at Chemical FormulasLook at Chemical Formulas

- C + O2 CO2

- This says that 1 carbon atom and an oxygen molecule create carbon dioxide

- The arrow means produces

- C o o C

Another Chemical EquationAnother Chemical Equation• HH22 + O + O22 H H22OO• 1 hydrogen molecule combines with 1 hydrogen molecule combines with

1 oxygen molecule to produce water.1 oxygen molecule to produce water.• Problem with the equation—what is Problem with the equation—what is

it?it?• Numbers do not balance on each Numbers do not balance on each

sideside– Look at the oxygen atomLook at the oxygen atom

Correcting the water equationCorrecting the water equation

• H2 + O2 H2O• There are 2 hydrogen atoms on each side

so that is correct• There are 2 oxygen atoms on the left side,

but only one on the right side. • You need to balance both sides• 2H2 + O2 2H2O• Now there are even number of atoms on

each side (4 hydrogen, 2 oxygen)

Lets try another oneLets try another one• P4 + O2 P2O3

• How many phosphorous atoms on each side?–4 on the left, 2 on the right

• How many oxygen atoms on each side?–2 on the left, 3 on the right

• What can we do to balance it?• P4 + 3O2 3P2O3

Let’s practice againLet’s practice again

• N2 + H2 NH3

• How many nitrogen and hydrogen atoms on each side?–Left: 2 nitrogen and 2 hydrogen

–Right: 1 nitrogen and 3 hydrogen

• How can we balance it?• N2 + 3H2 2NH3

another—you WILL understand another—you WILL understand thisthis

• AlBr3 + K KBr + Al• What elements are involved?

–Aluminum, bromine and potassium• How many atoms of each element are on

each side of the equation–Left side: 1 aluminum, 3 bromine, 1

potassium–Right side: 1 potassium, 1 bromine and

1 aluminum

So the answer to the questionSo the answer to the question

• What is the balanced equation–AlBr3 + 3K 3KBr + Al

• How many atoms of each element are there now on each side–Left side: 1 aluminum, 3 bromine,

3 potassium–Right side: 3 potassium, 3 bromine

and 1 aluminum

Now for a harder oneNow for a harder one

• LiNO3 + CaBr2 Ca(NO3)2 + LiBr

• What atoms are involved?

–Lithium, nitrogen, oxygen, calcium, bromine

• How many atoms on each side?–Left: 1 Li, 3 O, 1 Ca, 3 Br

–Right: 1Ca, 2 N, 6 O, 1 Li, 1 Br

What is the balanced equationWhat is the balanced equation• 2LiNO3 + CaBr2 Ca(NO3)2 + 2LiBr

• How many atoms are there now?

• 2 Li, 2 N, 6 O, 1 Ca, 2 Br on each side.

CoefficientCoefficient

• Those numbers we added to the front of the formula is called the coefficient.

• This is how you balance an equation.

THE ENDTHE END