The Periodic Table and Covalent Bonding – Revision Pack (C4)
Covalent Bonding:
Non-metals can share electron pairs between atoms – this is known as covalent
bonding. The idea of covalent bonding is that when the elements react, they gain
electrons to fill their outer shell and become stable.
When the atoms join together, there is a strong bond that holds them together –
covalent bonds. The formation of simple molecules that contain single and double
bonds can be represented by ‘dot and cross’ diagrams which only show the outer
shells electrons. For example:
H2O has two single covalent bonds. Two
pairs of electrons are shared.
Oxygen atoms can each form two
covalent bonds. Two pairs of electrons
are shared in an O2 molecule – this is a
double bond.
Predicting chemical properties:
The attraction between molecules like carbon dioxide and water is called an
intermolecular force.
The dot and cross diagrams for water and carbon dioxide represent how ALL the
atoms bond to make a molecule – this means that you have to show ALL the
electrons in each of the atoms.
Carbon dioxide is made up of two oxygen and one
carbon atom. The carbon atom has four electrons in its
outer shell, so it needs four more. Oxygen atoms have
six electrons in its outer shell, so needs to more. Two
double covalent bonds are created – each oxygen
outer shell is shared with two of the electrons from the
carbon outer shell. This way all of the atoms have a full
outer shell.
The simple molecular structures, like CO 2 , have weak intermolecular forces so are
very easy to break apart so the substances have low melting points.
In covalent bonding there are no free electrons so these molecules do NOT conduct
electricity.
Groups and Periods:
The group number (columns) is the same as the number of electrons in the outer
shell.
The period number (rows) is the number of shells needed for all the electrons.
The Periodic Table and Covalent Bonding – Revision Pack (C4)
The development of the periodic table:
Scientist
Discovery
Newlands
1865 – Newlands puts 56 elements into groups and noticed that
every 8 elements behaved similarly. This was not accepted for
another 50 years until other scientists discovered more
evidence.
Mendeleev
1869 – Mendeleev put all the elements in order in a table. He
noted periodic changes in the elements and made the
prediction that new elements would be discovered.
1891 – Mendeleev did not include the noble gases in his
periodic table.
After 1891 – Later investigations by other scientists confirmed
Mendeleev’s idea of periodicity. His prediction that other
elements would be found are correct.
The Periodic Table and Covalent Bonding – Revision Pack (C4)
Past Paper Questions:
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The Periodic Table and Covalent Bonding – Revision Pack (C4)
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The Periodic Table and Covalent Bonding – Revision Pack (C4)
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