Grade 9 Academic Science – Chemistry
Bonds
Section 7.1
IONIC BOND
The formation of a bond resulting from the transfer
of one or more electrons from a metal onto a nonmetal.
An ionic bond is the complete transfer of
electrons. As shown in the diagram, Na becomes
positive (i.e., Na lost e-) and Cl becomes negative
(i.e., Cl gained e-).
COVALENT BOND
The bonding between non-metals. The bond
consists of two electrons shared between two
atoms. In covalent bonding, the two electrons
shared by the atoms are attracted to the nucleus
of both atoms. Neither atom completely loses or
gains electrons.
There are two types of covalent bonding.
 Non-polar bonding with an equal sharing
of electrons between identical non-metals
(exception carbon/hydrogen). Since there is equal sharing of electrons, neither atom can
dominate the other. Therefore, the electrons are shared equally.
 Polar bonding with an unequal sharing of electrons between two different non-metals.
The number of shared electrons depends on the number of electrons needed to complete
the octet. As shown in the diagram, there is unequal sharing. Chlorine has a greater
tendency to keep its own electron and also draw away hydrogen's electron. It is NOT
completely successful. As a result, only partial charges are established. Hydrogen
becomes partially positive since it has lost control of its electron some of the time (H+);
whereas, chlorine becomes partially negative since it gains hydrogen's electron some of
the time (Cl-).
Why do non-metals share electrons?
The chemistry term is electronegativity. Electronegativity is a measure of how much an element
pulls electrons away from other elements. Metals generally have very low electronegativities (i.e.,
they don't much want to grab electrons) while nonmetals have high electronegativities (i.e., they
really want to grab electrons). Why? The octet rule says all elements want to have the same
number of electrons as the nearest noble gas (noble gases are unusually stable). When metals
bond to non-metals, ionic compounds are formed because the metal atoms do not want electrons
and easily give them to non-metals that want electrons. It is a different story when two nonmetals. Instead of having one element give electrons to another, we run into a case where the
two elements similar electronegativity attraction. To have an electron configuration similar to their
nearest noble gas, the two non-metals have to share electrons. In this fashion, the covalent
compound forms distinct molecules in which the atoms are bound tightly to one another.
In ionic compounds, the molecules interact. In a covalent compound, there is not interaction with
each other much (except through relatively weak forces called "intermolecular forces"). This
characteristic of the covalent compound makes them easy to pull apart.
DIATOMIC MOLECULES
There are seven elements that form diatomic (elemental) molecules
 Hydrogen (H2)
 Nitrogen (N2)
 Oxygen (O2)
 Fluorine (F2)
 Chlorine (Cl2)
 Iodine (I2)
 Bromine (Br2)
An easy-to-remember mnemonic for the diatomic elements: Have No Fear Of Ice Cold Beer
MONATOMIC or MONOATOMIC ELEMENTS
Elements are stable as single atoms. Mon- or Mono- means one. For an element to be stable by
itself, it needs to have a stable octet of valence electrons (i.e., full outer electron shell). The Noble
Gases exist as monatomic elements.
 Helium
 Neon
 Argon
 Krypton
 Xenon
 Radon
Challenge Questions
Working in groups of 4-6 colleagues, try to find a logically answer, based on your understanding
of chemistry, for the following questions. NOTE: Some clues are available in the information
provided.
1. Why do most covalent compounds NOT dissolve in water?
2.
Why do covalent compounds NOT conduct electricity?
3. Why do metals not bond covalently?
4. Covalent compounds have low melting or boiling points than ionic compounds. Why?
Challenge Questions - Answers
1.
Why do most covalent compounds NOT dissolve in water?
"Like dissolves like". This means that compounds tend to dissolve in other compounds that have
similar properties (particularly polarity). Since water is a polar solvent and most covalent
compounds are fairly non-polar, many covalent compounds do not dissolve in water.
2.
Why do covalent compounds NOT conduct electricity?
Electricity is conducted in water from the movement of ions from one place to the other. These
ions are the charge carriers which allow water to conduct electricity. Since there are no ions in a
covalent compound, they do not conduct electricity in water.
3.
Why do metals not bond covalently?
4.
Covalent compounds have low melting or boiling points than ionic compounds. Why?
Ionic compounds have very high melting and boiling points because it takes a lot of energy for all
of the + and - charges which make up the crystal to get pulled apart from each other. Essentially
with an ionic compound, all of the ionic bonds must be broken in order to make it melt. On the
other hand with covalent compounds, there are no bonds to break. This is because covalent
compounds form distinct molecules, in which the atoms are bound tightly to one another. Unlike
in ionic compounds, these molecules do not interact making them very easy to pull apart from
each other. Since they are easy to separate, covalent compounds have low melting and boiling
points.