Transcript Covalent Compounds

Covalent
Compounds
Covalent Bonds
 Atoms of two nonmetals combined
 Held together by sharing electrons
 “co” means cooperate/share
 “valent” refers to the valence electrons
 Atoms bonded with covalent bonds are called molecules
Covalent molecules
 Atoms with covalent
bonds share electrons
to achieve an octet for
each of them
 Some elements exist in
nature as
diatomic molecules
= molecules that contain
two like atoms
* Note the names
Sharing Electrons Between Atoms
of Different Elements
 The number of
electrons that an
atom shares and the
number of covalent
bonds it forms are
usually equal to the
number of electrons
needed to acquire a
noble gas
arrangement
Exceptions
 Although the nonmetals typically form octets,…
 Some (P, S, Cl, Br, and I) can share more valence
electrons and form stable valence shells of 10 or
12 electrons
1A
3A
4A
5A
6A
7A
B
3 bonds
C
4 bonds
N
3 bonds
O
2 bonds
F
1 bond
Si
4 bonds
P
3 (or 5)
bonds
S
Cl, Br, I
2 (4 or 6) 1 (3 or 5)
bonds
Bonds
H
1 bond
Multiple Covalent Bonds
 In many covalent compounds, atoms may
share 2 or 3 pairs of electrons to complete
their octets
 Double bond  2 pairs of e- shared
 Triple bond  3 pairs of e- shared
 C, O, N, and S are most likely to form
multiple bonds
 Atoms of hydrogen and the halogens do not
form double or triple bonds
Naming Covalent Compounds
 1st nonmetal uses
its elemental name
 2nd nonmetal uses
its elemental name
with the –ide
ending
 Subscripts are
expressed as
prefixes placed in
front of each name
Prefixes for numbers used in
naming covalent compounds
1
Mono
2
Di
3
Tri
4
Tetra
5
Penta
6
Hexa
7
Hepta
8
Octa
9
Nona
10
Deca
The names of covalent compounds need
prefixes because several different compounds
can be formed from the same two nonmetals
Ex) carbon + oxygen can form
CO (carbon monoxide) or
CO2 (carbon dioxide)
In the name of a covalent compound, the prefix
mono is usually omitted on the 1st atoms name
When the vowels o and o or a and o appear
together, the first vowel is omitted
Practice
naming covalent compounds
Name each of the following covalent
compounds:
a) NCl3
b) N2O4
Nitrogen trichloride
Dinitrogen tetroxide
Write the formula of sulfur dichloride.
SCl2
Naming and Writing Formulas
Naming Binary Molecular Compounds
The prefix tells how many atoms of each element are present in each
molecule of the compound
Carbon Monoxide vs. Carbon Dioxide
Mono- indicates one oxygen
Di- indicates two oxygens
Naming and Writing Formulas
Guidelines for Naming
1) Confirm the compound is a molecular compound (2 nonmetals)
2) Omit mono- when the the formula contains only one of the first
element in the name
3) Add -ide to the second element in the formula
Guidelines for Formula Writing
1) Use the prefixes in the name to tell you the subscripts in the formula
Naming and Writing Formulas
Practice
Write the name of these molecular compounds:
a) NCl3
b) BCl3
c) NI3
d) SO3
e) N2H4
f) N2O3
Naming and Writing Formulas
Practice
Write the formulas for these binary molecular compounds:
a) Phosphorus pentachloride
b) Iodine heptafluoride
c) Chlorine trifluoride
d) Iodine dioxide
e) Carbon tetrabromide
f) Diphosphorus trioxide
Summary of naming rules
Binary Compounds (may be ionic or covalent) 
State the 1st element, followed by the 2nd element with an –ide ending
If 1st element is 
a metal = ionic compound
nonmetal = covalent compound
Ionic compounds 
Is the 1st able to form more than one ion? …
…if so, use Roman numerals to indicate charge
Compounds with polyatomic ions use –ate or –ite endings
(determined by # of oxygens)
* Exception NH4+ written 1st
Covalent compounds 
Prefixes are needed to show # of atoms of each nonmetal in the formula
Organic Compounds