6.1 Elements Combine to from Compounds
 Compounds form when two or more different
atoms combine.
 Properties of compounds depend on which
atoms are in the compound and how the atoms
are arranged.
 Properties of compounds are different than that
of just elements that make them up.
Ex) Water is made out of Hydrogen and Oxygen, and H
and O are both colorless gas at room temperature. But
when these two elements make a compound, they are
liquid at room temperature.
Compounds always contain atoms with a
specific ratio.
Ex) Ammonia (NH3)has a 3:1 (3 to 1) ratio of
hydrogen to nitrogen
If this ratio was different, we would not have
ammonia anymore. For example if we had a 1:3 ratio
of hydrogen to nitrogen we would not have a
compound called Hydrazoic Acid (HN3).
Ammonia (NH3)
Hydrazoic Acid (HN3)
Chemical formulas like that for ammonia,
NH3, uses the chemical symbols for the
element to represent the atoms in a
compound.
Ex) Carbon dioxide has one carbon and two
oxygens in it.
Step 1: Find the chemical symbols for the elements
 Carbon—C
 Oxygen—O
 Write these side by side–CO
Step 2: To show that there are two oxygens, you
must write a “2” by it on the right in a subscript.
Step 3: Now you have your compound—CO2
Counting Atoms
Directions:
1. Write down the different elements in each
compound.
2. Write down how many of that particular atom there
are
3. How many atoms are there total in the compound.
2 H2SO4
2 Mg(SO)4
1) CH4
2) 4 HNO3
3) 4 Mg(OH)2
4) MgCl2

5) 4 Li2O
6) (NH4)3PO4
Bonding and Valence Electrons
1. Atoms bond because they want to be
Stable
________________.
Stable
2. Atoms are _____________
when they have
8 electrons in the outer shell. (Octet Rule)
___
8
3. In order to get ___ electrons in the outer
give
shell, atoms _________,
_________
take
share
or__________
electrons with/from other atoms.
Noble Gases
4. The 18th Group, the _______________are
already stable.
Valence Electrons
Electrons in the outer shell are called
_________________electrons
valence
Valence electrons
____________________
are the electrons
responsible for bonding two atoms
together
Noble gases are stable because they have
8 valence electrons; all other atoms
____
want the stability that noble gases have
Valence Electrons (Continued)
The number of Valence electrons can be
group
determined by the number of the ___________
Group #1 has ____
1 valence electron;
2 valence electrons;
Group #2 has ____
7 valence electrons
Group #17 has ____
Chlorine—Halogen
Sodium—Alkali Metal
Ionic Bonding Notes
Ions are formed when atoms
gain
lose
______________
or ____________
electrons
Losing
___________
electrons makes a positive ion
Gaining
___________
electrons makes a negative
ion
8 electrons
Metals lose electrons to have ___
in their outer shell
gain electrons to have 8
Nonmetals ______
electrons in their outer shell.
Ionic Bonding
 Ionic bonds form when there is an attraction
between positive and negative ions.
 We know that the Alkali Metals like to form
positive ions (lose e-), and the Halogens like to
form negative ions (gain e-).
 This means that if Sodium (Na) loses an
electron, Chlorine (Cl) will pick it up. We now
have a sodium ion (Na+) and a chloride ion (Cl-).
 These opposite charges will attract one another
and they will bond and this is called an ionic
bond.
Ionic Bonding (Continued)
Chlorine, a nonmetal,
makes a negative ion
Chlorine
Sodium, a metal,
makes a positive ion
Sodium
OPPOSITES ATTRACT
Naming Ionic Compounds
 The name for the positive ion stays the same from the
atom from which it was formed.
 The name for the negative ion is formed by dropping the
last part of its name and adding the suffix “–ide” to it.
 To complete the name of the compound put the positive
ion first followed by the negative ion.
Ex) Table salt
Na+ and Cl- come together to form NaCl
Na+ is now “sodium”
Cl- was chlorine, but since it is the negative ion it
changes to “chloride”
Result: sodium chloride
Covalent Bonds
covalent bond
A __________is
a pair of shared electrons
nonmetals
between two atoms that are________.
When forming covalent bonds, neither
gains
loses
atom ______or
_____
electrons, so no ion
is formed.
Covalent bonds are often represented by a
line between two atoms. Most common is
the ball-and-stick model.
Covalent Bonds (cont.)
 The number of covalent bonds that an atom
can make depends on the number of
Valence electrons
____________that
it has.
Ex) The Halogens (Group 17) and Hydrogen only
7
have ___valence
electrons. This means that they
can only form one covalent bond.
6
Ex) The atoms in Group 16 have ___
valence
electrons. This means that they can from two
covalent bonds.
 Remember that all atoms want to be stable and have
8
____valence
electrons.
Ex) The atoms in Group 15 ( 5 valence e-) can form
three
______covalent
bonds.
Ex) The atoms in Group 14 (4 valence e-) can from
four
______
covalent bonds.
Covalent Bonds (cont.)
four
Ex) Methane, CH4, can form _____
four
covalent bonds because carbon has ____
valence electrons. These are all single
bonds because carbon is sharing only
one
_____
pair of electrons with each
hydrogen.
Double Bonds
When atoms share more than one pair of
double bond
valence electrons, a _________can
from.
two pairs
A double bond forms when ________
of
valence electrons are shared.
Ex) The carbon atom in carbon dioxide,
CO2, forms double bonds with each
oxygen
_________
atom.
Triple Bonds
A triple bond forms when an atoms share
three pairs of valence electrons.
____
Ex) Two nitrogen atoms can because they
have 5 valence electrons each atom, and
they want 8.
Because they want to get to 8, they each share
3 valence electrons. This results in the two
6
nitrogen atoms sharing ____electrons,
or three
pairs.
N
N
A group of atoms held together by
molecule
covalent bonds is called a________.
Molecules can have anywhere from two to
thousands
_________of
atoms in them.
Some molecules have only atoms of one
element.
diatomic
These are called _______molecules.
H2, N2, O2, F2, Cl2, Br2, and I2
Polar Covalent Bonds
 In a iodine (I2) molecule, both atoms are the
same and the shared electrons are attracted
equally to both nuclei.
 If the two atoms involved in a covalent bond
very different
are __________then
some electrons will be
attracted to one nucleus more than the other.
 A covalent bond in which the electrons are
shared unequally is called a
Polar covalent bond
______________.
Remember that “polar” means that something has
to extremes, like a magnet with to opposite poles.
Polar Covalent Bonds (cont.)
 In a water molecule (H2O), the oxygen atom
attracts electrons more strongly than
hydrogen atoms do.
Because oxygen has eight protons in its nucleus
and the hydrogen only has one proton, the oxygen
pulls electrons stronger towards it. This means that
the oxygen side has a slightly negative charge and
the hydrogen side has a slightly positive charge.
Ionic Compounds
Most ionic compounds have a regular
crystal structure.
Their structures depend on the ratio of
their atoms and the sizes of the ions that
make them up.
Covalent Compounds
 Unlike ionic compounds, _______
compounds can
covalent
exist as individual molecules.
 Chemical bonds give each molecule a specific,
molecular
three-dimensional shape called its ________
structure.
molecule
 Molecular structure can influence how a ________
interacts with other substances.
 Molecular structure can also affect how we detect
them or how our bodies respond to them.
Molecules with certain shapes will fit into certain
receptors in our nose that we can smell.
Some drugs work while other don’t because specific
receptors in the body only allow certain shapes to fit.
Lewis Dot Structures
These depend on the number of valence
electrons. These are the outer-most electrons.
polar covalent
bond
ionic bond