
Be sure you memorize the list of polyatomic ions that you have been provided.




Covalent (co—sharing; valent—outermost shell)
 when electrons are shared between 2 nuclei

Molecule- a group of atoms held together by covalent bonds

In covalent bonding, the atoms are able to achieve an octet through the sharing of electrons


Are held together by the attraction of electrons of one atom and the nucleus of a second atom

Their bonds are flexible, somewhat like springs

A single bond forms from a single pair of shared electrons


Molecular compound names include prefixes that indicate the number of atoms in the molecule

They are composed of nonmetal elements


Write the name of the least electronegative element with a prefix to indicate the number of atoms of the element that are present

Prefix mono- is NOT written with the first word of a covalent compound’s name

Write the name of the most electronegative element second with a prefix to indicate the number of atoms of the element that are present

# of atoms
Prefix # of atoms
Prefix
3
4
5
1
2
Mono-
Di-
Tri-
Tetra-
Penta-
8
9
10
6
7
Hexa-
Hepta-
Octa-
Nona-
Some prefixes are sometimes shortened to make a name easier to say
(aka: you may have to remove the “a”)
Deca-


Suffix –ide is added to the name of the last element

Examples:

CCl
4
– carbon tetrachloride

NO- nitrogen monoxide

1.
What are the differences between ionic and covalent bonds?
2.
Name the following covalent compounds: a) S
2
O
3 b) CO
2 c) PBr
5


Atoms bond to obtain a full set of 8 valence electrons
(octet rule)

Lose or gain e- (ionic bonded)

Sharing e- (covalent bond)

Molecule – 2 or more atoms bond covalently, usually nonmetals

DIATOMIC MOLECULES (Be able to write 7 diatomic elements with correct formulas – hint: the elements form a 7 plus H
2
)

H
2
, N
2
, O
2
, F
2
, Cl
2
, Br
2
, I
2


Lewis dot structures: use e- dot diagram to show how electrons are arranged in molecules
1.
Draw Lewis dot structure of element (valence e- around symbol)
2.
Only draw dots on the four sides (top, bottom, left, right) of the atom
3.
Connect only single dots

Lone pair e- help shape molecules by pushing other atoms down


How many e- are shared by the groups?

Group 14 shares 4 e-

Group 15 shares 3 e-

Group 16 shares 2 e-

Group 17 and H share 1 e-

Single covalent bonds are also called sigma bonds (σ)

Covalent compounds can also have double bonds
(each shares 2 e-)

Covalent compounds can have triple bonds (each shares


2 PAIRS of shared electrons form a double bond
This is 1 DOUBLE BOND
O C O


So, what would a triple bond look like?

Each line represents 1 shared PAIR of electrons
N N
Is there something unusual here
?


H
2

CH
4

NH
3

H
2
O


Lower melting and boiling points vs. ionic

Molecules have no charge, hence do not conduct heat or electricity in any state.

Melting molecular compounds

Does NOT separate the clusters of atoms within a molecule,

Separates just molecules from each other


An acid is a molecular substance that dissolves in water to produce hydrogen ions

NOTE: ALL acids contain hydrogen…
BUT…Not everything with hydrogen is an acid!

They are covalent compounds that separate into a cation and an anion in water (ionic tendency)



The name begins with the prefix hydro-

The name is derived from the anion

The suffix –ide should be changed to
–ic


One of the many uses for HC l is cleaning concrete, but it’s also found in your stomach…What is the name of this acid?

Some wheel cleaning compounds used in carwashes contain hydrofluoric acid. What is the formula for this acid?


Polyatomic acids:

Do not use prefix hydro-

The suffix –ate should be changed to –ic

The suffix –ite should be changed to –ous


In addition to its many other uses, nitric acid is commonly used in the woodworking industry to artificially age pine and maple. What is the formula for this acid?

What would be the name of HClO
2

H
2
CrO
4 was once widely used in the band instrument repair industry, because of its ability to “birghten” raw brass.
What is the name of this acid?

Binary compound yes
Is hydrogen the cation?
no yes
Use Acid naming rules yes no
Is hydrogen the cation?
no no
Use prefixes
Metal present no no
Polyatomic ion or ions present?
yes
Does the metal form more than one cation?
Not established yes
Use the polyatomic name as appropriate yes
Use element name
Use element name with proper Roman numeral

ite
Is oxygen in the anion yes
Check the ending of the anion name no
Hydro -
+ anion root
+ ic
Hydro (anion root) ic acid
ate anion or element root
+ ous
(root) ous acid anion or element root
+ ic
(root) ic acid


A diatomic molecule is a molecule formed from two identical atoms

The atoms join together because they are more stable that way than if they exist as single atoms

Remember HOFBrINCl

H
2
, O
2
, F
2
, Br
2
, I
2
, N
2
, and Cl
2


Not KNOWING the 14 polyatomics – correct formula and charges

Not KNOWING the charges of elements based on the periodic table.

Alkali metals are 1+, alkaline earth metals are 2+, aluminum is 3+, nitrogen group is 3-, oxygen group is 2-, halogens are 1-.

Transition metals (except zinc, cadmium, and silver) and metals in the P block have more than 1 charge.

Not putting the parentheses around hydroxide when there is more than 1.

OH
2 is water; (OH)
2 is 2 hydroxides

Not simplifying (if the charges are the same, no subscripts are needed)

Not using roman numerals correctly in the names.