Chemistry
Tutorial #4
Chemical Compounds
Elements – pure substance made of one
type of particle
 Compound – when two or more elements
combine
 Elements are held together by chemical
bonds
 Chemical bonds form when an element
gains,loses or shares an electron (charged
particle)

Chemical Formulas
Use symbols and numbers (subscripts) to
represent the composition of a pure substance
 Symbols for each element are used
 Subscript (#’s) represent the number of atoms
of each element
Eg. H2o – H=symbol of hydrogen
o=symbol for oxygen
2= 2 atoms of hydrogen
* note: if a symbol has no subscript it is said to
represent having 1 atom.

Molecular Compounds
Two types of compounds: Molecular and Ionic
 Ionic compounds form when two atoms transfer electrons to other
atoms
 Molecular compounds form when atoms share electrons
 Molecule is smallest unit of a pure substance (cluster of atoms)
 Diatomic molecule is a molecule made of two atoms of the same
element.
Eg. O, N, H are all diatomic and thus written as O2, N2, H2
 Most molecular compounds form sm.structures therefore, have
strong bonds between atoms but very weak bonds between
molecules.
 As a result, they have low boiling points and low melting points
Naming Molecular Compounds
Compounds are named by IUPAC (international union of pure and
applied chemistry) recommendations.
Binary compounds are made from two elements.
Rules for naming:
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1.
2.
3.
Write the name of the first element
Change the ending of the second to “ide”
Use a prefix to indicate the # of each type of atom
Mono=1 (only used for the second element)

Di = 2

Tri = 3

Tetra = 4
Eg. CO2  Carbon Dioxide

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To change from name to chemical formula

1.
2.
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Write the symbol for each element in the same order
Use subscripts to indicate the # of each atom.
When naming a compound, often it has sm.symbols in ( ) to indicate the
state of matter (s), (l), (g) or (aq) which = aqueous (solid dissolved in
water)
Naming Molecular Compounds
Try the following:
CO _____________________________
SiO2_____________________________
Carbon tetrachloride ________________
Sulfur Dioxide _____________________
Naming Molecular Compounds
Try the following:
CO carbon monoxide
SiO2 Silicon dioxide
Carbon tetrachloride CCl4
Sulfur Dioxide SO2
Ionic Compounds
Form when atoms transfer electrons
 An ion is formed when an atom gains or
loses an electron and is no longer neutral
 Ions always have a + or – charge
 When dissolved in water ionic compounds
separate into ions and thus carry an
electric current.

Naming Ionic Compounds

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Rules are similar to molecular
The main difference is the name doesn’t
indicate the #of ions in each element.
The Rules:
1.
2.
3.
Name includes both elements with the metallic element first
Non metallic element is second with “ide” ending
Subscripts indicate the ratio of ions in a compound.
Eg. CaCl2  calcium chloride (ratio = 1Ca to 2Cl
Try the following:
NaCl ______________
LiCl _______________
Sodium Fluoride ________
Zinc Sulfide ____________
Try the following:
 NaCl sodium chloride
 LiCl Lithium chloride
 Sodium Fluoride NaF
 Zinc Sulfide ZnS

Properties of Ionic & Molecular
Compounds
Ionic
Molecular
Formed from metallic
and non-metallic
elements
Forms ions in solution
Conducts electricity
Usually formed from
only non-metallic
elements
Doesn’t form ions in
solution
Non-conducting
Solid at room
temperature
Solid, liquid or gas at
room temperature
Chemical Reactions
Two or more substances combine to form
a new substance. Cannot be reversed.
 Reactants – substances that go into a
reaction.
 Products- what is formed in the reaction

Chemical equations
 How
chemists describe reactions
 Word equations and chemical
equations
 Chemical equations use symbols
Eg. Magnesium + oxygen 
magnesium oxide
Or 2Mg(s) + O2  2 MgO (s) + light
Balancing Chemical Equations

Remember the law of conservation of
mass?

It says that atoms can’t be lost or created.
The atoms essentially change partners.
Therefore, you will have the same # of atoms
of each element just combined differently.
Eg. HC2H3O2 (aq) + NaHCO3 (s)  NaC2H3O2 (aq) + H2O (l) + CO2 (g)
(vinegar)
(baking soda) (sodium acetate) + (water) + (Carbon dioxide)

Take a minute to add up the number of atoms of each
element on both sides of the equation
It is important to balance a chemical equation so that each side of
the equation has the same number of atoms of each element.
 To balance an equation you need to count the number of atoms of
each element on the each side of the equation and make both sides
equal by using co-efficiants
Eg. Magnesium + oxygen magnesium oxide
Step 1: write the chemical equation
Mg + O2  MgO *oxygen is a diatomic molecule
so it is always written O2
Step 2: count the # of atoms of each element.
1Mg & 2O
Step 3: balance the equation: there are 2 O’s on the left so we need 2
on the right. Mg + O2  2MgO
Step 4: now, we have 2 Mg on the right and only 1 on the left. So, use a
coefficiant. 2Mg + O2  2MgO
Step 5: count the atoms and make sure eveyone is happy! You now
have a balanced equation.

Balancing
Try the following:
CH4 +_ O  CO +_ H O
2
2
2
_H + O  _ H O
2
2
2
_Na + Cl _NaCl
2
_CaCO +_ H SO  _CaSO + _H O +_ CO
3
2
4
4
2
2
Balancing
Try the following:
CH4 +2 O  CO +2 H O
2
2
2
2H + O  2 H O
2
2
2
2Na + Cl 2NaCl
2
_CaCO +_ H SO  _CaSO + _H O +_ CO
3
2
4
4
2
2
Breaking Chemical Bonds

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Chemical bonds are forces that cause a group of
atoms to behave as a unit.
To break these bonds, energy must be added.
When bonds form energy is released
Energy is produced or absorbed during a
reaction.



Exothermic reactions- eg. combustion
Endothermic reactions eg. Baking cookies; baking soda
breaks down and release CO2 and puffs up the cookies
Eg. Corrosion – prevent by zinc / galvanization
Reaction Rate

You can increase or decrease the rate of a
reaction by:

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

Changing the temp.
Stirring
Changing size and conc. Of reactants
Catalysts – speed up a reaction without being
changed
Eg. Enzymes – these occur naturally in our bodies. Saliva
(contains enzymes) helps breaks down the starches in our
food

Inhibiter – slows down the reaction
Eg. Preservatives in food.
Quick Note:
Memorize the chemical names of common
chemicals. These are found on pg 442 -445 in
your text. This will be on your midterm!
 You should know the chemical formula’s for the
following:
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Vinegar
Table salt
Propane
Sugar (sucrose)
Glucose
Hydrogen peroxide