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You will be re-visiting…
The structure of the atom.
Why atoms want to lose or gain electrons.
Which type of materials use covalent or ionic bonding.
The properties that covalent and ionic bonding give to the material.
You need to be able to…
Name the components of an atom.
Understand how many electrons are in each orbital.
Describe the charge on each sub atomic particle.
Understand what an isotope is.
To draw dot and cross diagrams.
To draw ionic formula diagrams.
To name compounds which use these types of bonding
Atoms contain three sub-atomic particles called protons, neutrons and electrons.
The protons and neutrons are found in the nucleus at the centre of the atom, and the electrons are arranged in shells around the nucleus.
The atom
The charge in an atom
• Atomic heaven is to be neutral!• Atoms will share or steal electrons so
they can to obtain the structure of the Group 0 or Noble elements.
• This group reacts with very little at all!• By sharing or stealing electrons the
atoms bond to become compounds and therefore neutral!
Particle Charge
Relative Mass
Protons +1 1
Neutrons
0 1
Electrons
-1 0.0005
• There are two properties of sub-atomic particles that are especially important:
MassMassElectrical Electrical chargecharge
So now we look at the Periodic Table…
12
C6
Atomic Number = the number of protons in the nucleus.It is the smaller number in the box.
Atomic Mass = the number of protons and neutrons in the nucleus.It is the larger number in the box.
Here is the element Carbon
From these two numbers we can work out the number of electrons this element should have.
Carbon can also be an isotope
Isotopes have the same number of protons but a different number of neutrons. So isotopes have the same atomic number but a different atomic mass.12
6 C or 146 C
Other famous isotopes are uranium and radium
Where are the electrons?
The electrons are located in orbitals or shells around the nucleus.
The innermost orbital will take up to two electrons only.
The next three orbitals will take a maximum of eight electrons each.
Covalent Bonding
• Covalent compounds are formed when non-metal atoms react together.
• As these atoms come near their outer electrons are attracted to the nucleus of both atoms and become shared by the atoms.
• The shared electrons count towards the shells of both atoms and therefore help fill up incomplete electron shells.
Boardworks – Covalent Bonding
Examples of covalent bonding
Simple covalent bonds:
Water H2O
Ammonia NH3
Methane CH4
Oxygen O2
Giant covalent structures:
Graphite
Diamond
Properties of covalent compounds
Small numbers of atoms in the molecules.
Low melting and boiling points.
Most are gases or liquids at room temperature.
They do not conduct electricity.
They tend to be insoluble in water.
Ionic bondingMost ionic compounds contain a metal and a non-metal.
When metals react they lose outer shell electrons to leave a full electron shell.
This produces a charged atom (ion) with a + charge.
When non-metals react with a metal they gain electrons to achieve a full electron shell.
© Boardworks Ltd 2003
Ions and electron structures
Metals lose electrons to form positive(+) ions called cations.
Non-metals gain electrons to form negative (–) ions called anions.
n+
n-
We know that the atoms lose or gain electrons to achieve full electron shells.
To understand more about how ionic compounds form we must look at what is happening to the outer shell electrons.
© Boardworks Ltd 2003
Formation of Sodium Chloride- the overall process.
ClNa
Na Cl
Sodium loses itsouter electron.Chlorine gains it.The result is both end up with full shells
Two oppositelycharged ionsare formed, which attract.Millions of such pairs form a giant lattice
© Boardworks Ltd 2003
Simpler electron diagrams
We can assume full inner electron shells. We can therefore sometimes shorten bonding diagrams by omitting to draw the inner electron shells.
Na Cl
Na Cl
© Boardworks Ltd 2003
OMg
2.8.2. 2.6
Magnesium atom
Oxygen atom
Bonding in Magnesium Oxide
More than one electron may be transferred between atoms in ionic bonding.
Mg2+ O2-
2.82.8
Magnesium Oxide
© Boardworks Ltd 2003
Sodium Fluoride
Sodium atom
Fluorineatom
Copy the diagram and draw another box showing the electron configuration in sodium fluoride.
Na+
2.82.8
FNa
2.8.1. 2.7
F-
© Boardworks Ltd 2003
More Complicated Formulae
• Ionic compounds may contain ions consisting of groups of atoms rather than a single atom.
• Here are some more complicated ions you may come across.
Atoms presentChargeFormulaIon
2-
1-
1+
2-
1-
CO32-
OH-
NH4+
SO42-
NO3-
carbonate
hydroxide
ammonium
sulphate
nitrate N O O O
OS OOO
N H H H H
O H
C O O O
Examples of ionic structures
Animation of NaCL
Properties of ionic compounds
Atoms are held very strongly together.
The compound has a regular structure.
Ions form giant structures.
Very high melting and boiling points.
Soluble in water.
Conducts electricity when dissolved.
OK, have a go at this quiz and check what you should
know