Transcript Covalent Compounds, Formulas and Naming

Covalent Compounds, Formulas
and Naming
Covalent Compounds
• Covalent compounds are compounds formed from 2 or
more nonmetals.
Examples:
• H20 (water)
• CO2 (carbon dioxide)
• C6H12O6 (glucose)
• When two nonmetals react, they usually share electrons
so that all atoms involved end up with 8 valence
electrons (Exception: Hydrogen only needs 2)
– it requires less energy for them to share than to
donate/receive
– because they are only sharing electrons, they do not
end up with a charge
Covalent Bonds
• A covalent bond is a bond that is formed when
electrons are shared between atoms
– Because this type of bond does not depend on
attraction between different charges, covalent bonds
are much stronger than ionic bonds
• Single bond – one pair of electrons shared
• Double bond – two pairs of electrons shared
• Triple bond – three pairs of electrons shared
Naming Covalent Compounds
• The names of covalent compounds have prefixes
that tell us the number of atoms of each element
in the compound:
Number atoms
1
2
3
4
5
6
7
8
9
10
Prefix
mono
di
tri
tetra
penta
hexa
hepta
octa
nona
deca
When there is a prefix
that ends in an “a” or
“o” before oxygen, the
“a” or “o” is usually
dropped
i.e. tetroxide,
pentoxide,
monoxide
Naming Covalent Compounds
1) First you need to identify that the compound
is a covalent compound!
• Compound formed by 2 or more nonmetals
• Be careful with
polyatomic ions! They
are covalently bonded,
however they have an
overall charge so they
form ionic compounds!
Naming Covalent Compounds
2. If there is more than one atom of the first element, write the
appropriate prefix first.
• If there is only one of the first element, we do not write a
prefix
3. Write the name of the first element in the formula using its
full name directly after the prefix (they combine to form
one word).
4. Write the appropriate prefix for the second element.
5. Write the base name of the second element and change
the ending to –ide (like we did for anions in ionic
compounds).
prefix
name of 1st
element
prefix
Base name of 2nd
element + “ide” ending
mono- 1
di- 2
tri- 3
tetra- 4
penta- 5
hexa- 6
hepta- 7
octa- 8
nona- 9
deca- 10
Naming Covalent Compounds Practice
1) CO2
carbon dioxide
2) N2O
dinitrogen monoxide
3) CCl4
carbon tetrachloride
4) BCl3
boron trichloride
5) SF6
sulfur hexafluoride
6) N2O4
dinitrogen tetroxide
Writing Formulas for Covalent Compounds
1. Identify that a covalent bond is present
2. Use the prefixes to determine the subscript
after each element.
• DO NOT criss-cross
• DO NOT reduce the subscripts
X
subscript
Writing Covalent Formulas Practice
1) carbon monoxide
CO
2) disulfur tetrafluoride
S2F4
3) dichlorine monoxide
Cl2O
4) diiodine pentoxide
I2O5
5) boron tribromide
BBr3