Grade 8 Integrated Science Chapter 8 Lesson 2 on compounds, chemical formulas, and covalent bonds. An introduction to electron sharing.

1. Chapter 8.2 - Compounds, Chemical Formulas, and Covalent Bonds – p275-282 - page1
Vocabulary
• Covalent Bond (277) – a chemical bond formed when two atoms share one or more pairs of
valence electrons
• Molecule (278) – a group of atoms held together by covalent bonding that acts as a n
independent unit
• Polar Molecule (279) – A molecule that has a partial positive end and a partial negative end
because of unequal sharing of electrons
• Chemical Formula (280) – a group of chemical symbols and numbers that represent that
elements and the number of atoms of each element that make up a compound
Review
• Compounds are substances made up of
two of more different ________________
• Compounds and the elements that make
them up often have different properties
• Chemical _____________ join atoms
together.
• One way atoms from bonds is by sharing
____________ electrons
Covalent Bonds – Sharing Electrons
• When unstable, nonmetal atoms bond together, they bond by
______________ valence electrons.
• A covalent bond is a chemical bond formed when two atoms share
one or more ____________ of valence electrons.
• The atoms then form a ___________ covalent compound
A Noble Gas Electron Arrangement
•
An atom with less than eight valence electrons becomes stable by forming chemical bonds
until it has ________________ valence electrons.
•
The most chemically stable state for most atoms has the electron configuration of a
________________________.
•
Look at H2O
H2O Bonding

2. Chapter 8.2 - Compounds, Chemical Formulas, and Covalent Bonds – p275-282 - page2
Shared Electrons
• If the oxygen atom and each hydrogen atom share their _______________ valence electrons,
they can form two covalent bonds and become a stable covalent compound.
• Each covalent bond contains _____________ valence electrons.
• Since these electrons are shared, they count as valence electrons for ______________
atoms in the bond.
• In H2O, all three atoms combine sharing valence electrons. We know the compound is
stable because all ________________ atoms have eight valence electrons.
Double and Triple Covalent Bonds
•
•
A single covalent bond exists when two atoms share ___________ pair of valence electrons.
•
Triple covalent bonds exist when two atoms share ____________ pairs of valence electrons.
– Triple bonds are stronger than ___________ bonds.
Double bonds exist when two atoms share _________ pairs of valence electrons.
– Double bonds are ____________ than single bonds
Covalent Compounds
•
•
Covalent compounds usually have __________ melting points and low boiling points.
•
Covalent compounds are _______________ conductors of thermal energy and electricity
They are usually gases or liquids at ________________temperature, but they can also be
solids
Molecules
• A molecule is a group of atoms held together by covalent boning that acts as an
independent unit,
• Table sugar (C12H22O11) is a __________________ compound.
• One grain of sugar is made up of _________________ of sugar molecules.
• One molecule of sugar contains _________carbon atoms, ___________hydrogen atoms, and
__________oxygen atoms.
• The only way to break a molecule of sugar would be to chemically separate the atoms of C,
H, and O.

3. Chapter 8.2 - Compounds, Chemical Formulas, and Covalent Bonds – p275-282 - page3
Water and Other Polar Molecules
• In a covalent bond, one atom can __________________ the shared electrons more strongly
than the other atoms can.
• Consider H2O
– The _________________ atom attracts the shared electrons
more strongly than each hydrogen atom does.
– As a result, the shared electrons are pulled ______________
to the oxygen atom.
– Since electrons have a negative charge, the oxygen atom has
a partial ___________________ charge.
• A molecule that has a partial positive end and a partial negative
end because of unequal sharing of electrons is a ________________molecule.
Dissolving Molecules
• The charges on a polar molecule affect its properties.
• Sugar dissolves easily in water because sugar and water are____________________ .
• The negative ends of a ____________________ molecule pulls on the positive end of a sugar
molecule.
• Also, the positive end of a water molecule pulls on the negative end of the sugar molecule.
• This causes the sugar molecules to ___________________ from one another and mix with
the water molecules.

4. Chapter 8.2 - Compounds, Chemical Formulas, and Covalent Bonds – p275-282 - page4
Nonpolar molecules
• A hydrogen molecule, H2, is a __________________ molecule.
• Hydrogen atoms are identical, their attraction for a shared electron is equal.
• The carbon dioxide molecule, CO2, is also________________________.
• A nonpolar compound will not easily dissolve in a polar compound, but it will dissolve easily
in a nonpolar compound.
• Oil is an example of a nonpolar compound. It will
not dissolve in_____________________.
Chemical Formulas and Molecular Models
• A chemical ___________________ is a group of chemical symbols and numbers that
represent the elements and the number of atoms of each element that make up a
compound.
• Just as a recipe lists ingredients, a chemical formula lists the elements in a compound.
• For example, the chemical formula for carbon dioxide is CO2.
– CO2 is made up of carbon and _______________ atoms.
– The____________________ , or small number after a chemical symbol, shows the
number of atoms of each element in the compound.
– CO2 contains _______ atoms of oxygen bonded to ________ atom of carbon.
• When parentheses (“()”) are used, any subscript applies to all the elements inside the
parentheses.
Example:
Al2(SO4)3
_____ Aluminum
_____ Sulfur
_____ Oxygen

5. Chapter 8.2 - Compounds, Chemical Formulas, and Covalent Bonds – p275-282 - page5
Counting Atoms
Name each of the following chemical compounds and determine how many atoms of each
element are present:
1)
CaF2 ___1 Calcium, 2 Flourine_________________________________
2)
Be(OH)2 ____________________________________________________
3)
NO2 ______________________________________________________
4)
Al2(SO4)3 ___________________________________________________
5)
NH4NO3 ____________________________________________________
6)
S2F2 ______________________________________________________
7)
Na2CO3 ____________________________________________________
8)
CH4 ______________________________________________________