Complete the worksheet on
the structure of the atom
review of atomic structure and
bonding
• LEARNING GOAL – to review Y11 work
on the structure of the atom and
bonding
Types of bonding
Atoms can be bonded in three different ways:
Ionic bonding
Metal and non-metal atoms
Covalent bonding
Non-metal atoms only
Metallic bonding
Metal atoms only
Bonding occurs because atoms with incomplete outer
electron shells are unstable. By forming bonds, atoms
completely fill their outer shells and become stable.
All types of bonding involve changes in the number
of electrons in the outer shells of atoms.
Ionic compounds
Compounds that contain ions are called ionic compounds. These
compounds are usually formed by a reaction between a metal and
a non-metal.
Both the metal and non-metal atoms have incomplete outer
electron shells and so are unstable.
One or more electrons are transferred from each metal atom to
each non-metal atom. The metal and the non-metal atoms end up
with completely full outer shells and become very stable.
The positive and negative ions are strongly
attracted to each other. This electrostatic
attraction is called an ionic bond.
Sodium chloride
Sodium chloride is an ionic compound formed by the
reaction between the metal sodium and the non-metal
chlorine.
sodium
Na
+
chlorine
Cl
sodium chloride
NaCl
During the reaction, one electron is transferred from
each sodium atom to each chlorine atom.
Sodium chloride
Sodium has 1 electron in its
outer shell. If it loses this
electron, it will have no
partially-filled shells.
Chlorine has 7 electrons in its
outer shell. If it gains 1 electron,
it will completely fill its outer
shell.
-
+
Cl
Na
2.8.1
[2.8]+
2.8.7
[2.8.8]-
Sodium chloride
The positive sodium ions and the negative chloride ions are strongly
attracted to each other and form an ionic bond.
-
+
Na
Cl
More complicated ionic bonding
Sodium chloride and magnesium oxide are simple ionic
compounds. In each case, the metal and non-metal need to lose
and gain the same number of electrons.
Na
1 electron
Cl
Na+
Cl-
Mg
2 electrons
O
Mg2+
O2-
This is not always the case.
Sodium oxide
Sodium (2.8.1) needs to lose 1 electron but oxygen (2.6)
needs to gain 2 electrons. Therefore, two sodium atoms are
required for each oxygen atom.
Na+
Na
1 electron per
atom
Na
O2-
O
Na+
Magnesium chloride
Magnesium (2.8.2) needs to lose 2 electrons but chlorine (2.8.7)
needs to gain 1 electron. Therefore, two chlorine atoms are
required for each magnesium atom.
Mg
1 electron for each
atom
Cl-
Cl
Mg2+
Cl
Cl-
Covalent bonding
When non-metal atoms react together, they need to gain
electrons to fill their outer shell and become stable.
H
incomplete
outer shells
H
They can only do this if they share electrons with each
other.
both atoms have a
H
H
full outer shell
The atoms share electrons so there is a strong force that
joins the atoms together. This is called a covalent bond.
Covalent bonding and elements
Many elements exist as molecules – two or more atoms
joined by a covalent bond. Each atom has a full outer
electron shell and is therefore stable.
H H
O O
Cl Cl
Only the outer shell of electrons is involved in covalent
bonding. This means that the inner shells do not always
have to be included in diagrams.
Two ways to indicate a covalent bond are:
solid line
H –H
H – H
dot and cross
diagram
H
H
Covalent bonding in oxygen
Oxygen (2.8.6) needs 2 more electrons to have a
completely full outer shell.
To achieve this, it can share two electrons with another
oxygen atom. This creates a double bond.
O
O
O2 or O=O
O
O
Covalent bonding in nitrogen
Nitrogen (2.8.5) needs 3 more electrons to have a
completely full outer shell.
It can share three electrons with another nitrogen atom
to do this. This creates a triple bond.
N N
N
N2 or N≡N
N
Covalent bonding in compounds
Covalent bonding can take place between atoms of
different elements to create molecules of covalent
compounds. These covalent bonds can be single, double
or triple.
Both hydrogen (1) and chlorine (2.8.7) need 1 more
electron to fill their outer shell. By sharing one electron
each, they can fill their outer shells and become stable.
H
HCl or H Cl
Cl
Covalent bonding in water
Oxygen (2.6) needs 2 more electrons, but hydrogen (1)
only needs 1 more. How can these two elements be
covalently bonded?
The oxygen atom shares 1 electron with 1 hydrogen atom,
and a second electron with another hydrogen atom.
O
H
H
H2O or H O H
Covalent bonding in ammonia
How are nitrogen and hydrogen bonded in ammonia?
Electron
2.5
configuration
Electrons
needed
Ratio of
atoms
H
1
3
1
1
3
H
N
H
NH3 or H N H
H
H
N
Covalent bonding in methane
Electron
2.4
configuration
Electrons
needed
Ratio of
atoms
H
1
4
1
1
4
CH4
H
H
or H C H
H
C
H
H
C
H
How are carbon and hydrogen
bonded in methane?
More covalent bonding diagrams
Draw a line diagram to show the bonding in:
1.
hydrogen sulfide
2. carbon dioxide
3. ethane (C2H6)
H
H
S
H
O
C
O
H
H
C
C
H
H
H