Chemical Bonding
Ionic Bonds
• Ionic bonds are made between metal and
non-metal atoms
• Electrons are transferred from the metal
atom to the non-metal atom
• Metal atoms lose electrons form positive
ions called cations.
• Non metal atoms gain electrons form
negative ions called anions.
Metals
• Metal atoms lose electrons to form positive
ions (an atom that loses or gains electrons)
called cations.
E.g., Beryllium (Be) Group 2
Neutral atom
4+ P’s
4- E’s
0
Positive ion
4+ P’s
2- E’s
2+
Valence Electrons
The electrons in the outer shell of an atom, which determines its
power to combine with other elements
Non-metals
• Non-metal atoms gain electrons to form negative
ions called anions.
E.g., Carbon (Ca) Group 14
Neutral atom
6+ P’s
6- E’s
0
Negative ion
6+ P’s
10- E’s
4-
An example of ionic bonding…..
• Let us consider the
bonding in the substance
sodium chloride.
• Na+ + ClNa+Cl• In this reaction the
sodium (Na) atom loses 1
electron while the
chlorine atom accepts the
electron in the transfer
process.
NaCl
Thus we can say that sodium chloride is an
ionic compound
Ionic Compounds
Ionic Compound – A compound that contains positively
charged ions and negatively charged ions.
NaCl
Na+
Sodium ion
This charged
atom contains:
11+ Protons
+ 10- Electrons
-1
ClChloride ion
This charged atom
contains:
17+ Protons
+ 18- Electrons
+1
Sodium Chloride
• Thus NaCl
• Once these two ions (An atom that has
become charged be gaining or losing one
or more electrons) have been formed, they
will attract each other because of their
opposite charges
CaO
• Ca2+ + O2Ca2+O2• In this reaction the calcium (Ca) atom
loses 2 electrons while the oxygen (O)
atom accepts the two electrons in the
transfer process.
• Thus we can say that calcium oxide is an ionic
compound
Calcium Oxide
Ca2+ Calcium ion
20+ Protons
18- Electrons
2+
O2- Oxide ion
8+ Protons
10- Electrons
2-
Once these two ions have been formed, they will
attract each other because of their opposite charges.
There is an electrostatic attractive force present (like
charges repel and unlike charges attract) that creates
the chemical bond in the NaCl and CaO called an
ionic bond.
Let’s try one…..
• One example is sodium (Na) and
fluorine (F)
• Each atom wants to become stable
(more like the noble gases!)
• This means that Na wants to lose
one eˉ and F wants to gain one eˉ
• This process of electron
rearrangement explains the
formation of compounds such as
sodium fluoride (NaF)
Chemical Name: Sodium Fluoride
Chemical Formula:
Another example.....
Magnesium and Fluorine
Metal
12+ Protons
10- Electrons
2+
Mg2+ + F1-
Non-metal
9+ Protons
10- Electrons
1Mg2+F1-
Chemical name: Magnesium fluoride
Chemical Formula: MgF2
Predicting Ionic Charge
• Metals tend to form cations
• Non-metals tend to form anions.
Predicting Ionic Charge
The group number on the periodic table indicates the
number of electrons the atom will lose or gain.
• Group 1 elements form cations with one positive
charge.
• Group 2 elements form cations with two positive
charges.
• Group 3 elements form cations with three positive
charges.
• Group 17 elements form anions with one negative
charge.
• Group 16 elements form anions with two negative
charges.
• Group 15 elements form anions with three negative
charges.
Figuring out Ionic Charge
• For metals, it‘s the same as the
group number (the column number).
• For non metals, the charge is equal to
whatever number needs to be added
to the group number to get 8. Group 8,
(the noble gases), don‘t form ions as
they do not need to gain any electrons to
have a full outer shell
Naming Ionic Compounds
• Usually, the cation (positive ion) is written
before the anion (negative ion)
• The first word is the name of the element
where the cation originally came from
• The last word is the name of the anion
with the suffix “ide”
More to try……..
Potassium and Sulfur
Aluminium and Chlorine
Aluminum and Oxygen
Calcium and Fluorine
Bonding in Ionic Compounds
• According to the ionic electrostatic model, solids such as
NaCl consist of positive and negative ions arranged in a crystal
lattice.
• Each ion is attracted to neighbouring ions of opposite charge,
and is repelled by ions of like charge; this combination of
attractions and repulsions, acting in all directions, causes the ion
to be tightly fixed in its own location in the crystal lattice.
Sodium metal reacts with chlorine gas in a violently exothermic
reaction to produce NaCl (composed of Na+ and Cl- ions):
2Na(s) + Cl2(g) -> 2NaCl(s)
Crystal Lattice
• Strong forces between ions
make these compounds very
hard, therefore they are not
good electrical conductors
(ions are not able to move)
• They can however, conduct
electricity when dissolved in
water or heated above their
melting point
Properties of Ionic Compounds
Property
Ionic Compounds
General Description
Solid at room temperature
Forms crystal structures
Usually hard but very brittle (break vs. bend)
Melting Point
Generally quite high
(eg. NaCl = 801°C)
Solubility
Highly soluble in water
Conductivity in Solid State
Very poor conductors
Conductivity in Molten State (or dissolved)
Excellent conductors
Electrolyte (when dissolved)
Odour
Usually does not emit an odour in the solid
state
Molecular Compounds
• Molecular compounds are made up of uncharged
atoms
• When we looked at ionic compounds, we saw that
atoms of metals and non-metals bonded by swapping
electrons
• Molecular compounds occur when 2 atoms (both
non-metals) combine by sharing their electrons
• This is called covalent bonding
Examples of Covalent Bonds
• This is a water molecule
(H2O)
• In this case, the oxygen
atom needs two more
electrons, so two
hydrogen atoms each
share a pair of electrons
with the oxygen atom
Properties of Molecular Compounds
Property
Molecular Compounds
General Description
Solid, liquid, or gas at room temperature
Forms crystal structures
Usually soft at room temperature
Melting Point
Generally low (compared to ionic)
Solubility
Insoluble in water
Conductivity in Solid State
Very poor conductors in any state
Conductivity in Molten State (or dissolved)
Poor conductors in any state
Odour
Many covalent substances emit a
strong/distinctive odour at room
temperature.
What is the difference?
• In general, the strength of covalent bonds is
about the same as ionic bonds
• The difference is the attraction between
molecules
• An ionic compound behaves like one large
structure, with each ion surrounded by ions of
opposite charge – strong attraction through the
crystal
• In molecular compounds, the bonding between
atoms is strong but the attraction between
molecules is weak.