Review of Chemical Bonding
Chemical bonding is the force of attraction between atoms or ions as a result of the interactions among
valence electrons. Elements can be generally classified as either metals or nonmetals. The type of
bonding that occurs is related to the types of elements involved.
I.
METALLIC BONDING (involves metals alone)
METALS tend to lose valence electrons in chemical bonding to form positive ions! Identical metal
atoms inside metal crystals each tend to “lose” their outer electrons to the space between positivelycharged metal ions. A metal crystal can be described as a regular structure of metal ions surrounded
by a “sea” of delocalized electrons. The electromagnetic force attracting the positively-charged metal
ions to the negatively-charged sea of electrons holds the metal together as a material. This type of
bonding is called Metallic Bonding.
II.
IONIC BONDING (involves metals + nonmetals)
While metals tend to lose electrons to form positive ions, NONMETALS tend to gain electrons to form
negative ions when they react chemically with metals. The positive ions formed by the metal atoms
and the negative ions formed by the nonmetal atoms are then attracted to each other due to opposite
electric charges to form an ionic compound. This type of bonding is called ionic bonding and is strong.
The number of positive charges and the number of negative charges in an ionic compound are always
balanced. This balance of charges is reflected in the chemical formula of an ionic compound.
The number of electrons needed to fill a nonmetal atom’s outer shell determines how many electrons
are gained by the nonmetal atom. Compounds formed by ionic bonding are usually solids.
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III.
COVALENT BONDING (involves nonmetals only)
Nonmetals all tend to gain electrons to get a full valence shell of electrons. So a nonmetal atom will
not lose its outer electrons to another nonmetal atom, but rather the nonmetal atoms will chemically
SHARE some valence electrons. The number of electrons shared is usually the number needed to fill
the valence shell. This type of bonding is called a covalent bonding.
The number of electrons shared per covalent bond is two, but there can be double bonds (four electrons
shared) and even triple bonds (six electrons shared) between some elements.
The number of covalent bonds that an atom will form depends on the number of electrons needed to
fill the its valence shell; this may be called a bonding rule. The basic covalent bonding rule can be
determined by looking at the periodic table, which shows the number of electrons in the valence shell
of an atom and, hence, the number of electrons needed to fill the shell (period 1 elements fill to two,
but other elements fill to 8).
Covalently bonded atoms form molecules. Molecules are electrically neutral (but may become
charged as a result of chemical reactions). In some cases, covalent bonding between a huge number of
atoms results in large network (giant molecular) structures, e.g., proteins, DNA, diamond, glass. But
in other cases, covalent bonding between a relatively few atoms results in the formation of small
molecules, which can be gases, liquids, or solids. Molecule are variably attracted to other molecules
depending on the size/mass of the molecules. Compared to the covalent bonds between the atoms
within a molecule, however, the force of attraction between molecules is relatively weak.
The structure of molecules is very important to their properties. These “structural formulas” show the
atoms of each element in the molecule with the atomic symbol and the bonds between atoms with a
line (single bond = 1 line; double bond = 2 lines; triple bond = 3 lines).
Complete the Exercise on the next page.
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Exercise 1
Name _______________________ Date _______
1. What type of chemical bond would be expected to form between the following pairs of atoms?
a) Al and Cl _____________
d) S and O _____________
b) N and O
_____________
e) Ba and Cl _____________
c) K and F
_____________
f) Fe and O
_____________
2. Will the chemical reactions of the following elements form IONS or MOLECULES?
a) fluorine and hydrogen
__________________________
b) hydrogen and oxygen
__________________________
c) potassium and chlorine
__________________________
d) silicon and oxygen
__________________________
e) carbon and sulfur
__________________________
f) sodium and sulfur
__________________________
g) iodine and sodium
__________________________
h) beryllium and phosphorus
__________________________
3. Draw the structural diagrams of the following molecules.
a) H2
b) H2O
c) CH4
d) NH3
e) N2
f) CO2
g) O2
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