Atomic Structure
Bonding
Summary
Atomic Structure
- Atoms contain protons, electrons and neutrons
- Protons and neutrons exist in the nucleus.
- Electrons exist in a series of energy shells around the outside of the nucleus.
Bonding
- There are three main types of bonding:
1. Ionic bonding
- between a metal and a non-metal, in which electrons are fully transferred.
2. Covalent bonding
- between non-metals and metals, in which electrons are shared.
3. Metallic bonding
- between metals, in which positive metal ions are held together by a negative electron cloud.
History of the Atom
The idea of the atom was first thought up by Democritus an ancient Greek philosopher, 2000 years ago.
However without any evidence people were rather sceptical.
Then, 200 years ago John Dalton did some experiments which showed that simple compounds always contained the same proportion of elements.
He explained his evidence with the idea that elements were made up of tiny particles which could not be broken down any further.
Now we have a slightly different idea.
What’s in a Atom?
Atoms have a small central nucleus made up of protons and neutrons around which there are electrons.
Neutron - Relative Mass 1 Relative Charge 0
Proton - Relative Mass 1 Relative Charge +1
Electron negligible -1
 
The Hairy Bikers Experiment
The scientists use hairy bikers to demonstrate what an atom looks like.
When the bikers arrive, note how the rings that they form with their motorbikes show how the electrons orbit the nucleus and gradually fill up each shell around that nucleus until they finish with Neon as a full shell.
Exam tips: Learn how to represent all the partially filled shells up to Calcium and the maximum number of electrons that can occupy each shell.
Exam Questions:
∙ Draw the electron arrangement for the following elements. Example Sodium atomic number 11 has an arrangement of 2,8,1
∙ Draw the electron arrangement for Beryllium atomic number 4, Aluminium atomic number 13 and Potassium atomic number 19.
Energy Shells
Electrons occupy particular energy levels.
These energy levels are called shells.
- The first shell can only contain 2 electrons
- The second shell can contain 8 electrons
- The third shell can contain 18 electrons
 
You should be able to represent the electronic structure of the first twenty elements of the periodic table in the following forms:  (notice that this is the unusual isotope of magnesium with only 11 neutrons, but this does not affetc its electronic arrangement).
Balloons
By setting fire to balloons filled with Hydrogen and Helium, the students show how just one single electron can make a lot of difference to the reactivity. Hydrogen has 1 electron, Helium 2 in their outer shells. Helium’s shell is complete and so very unreactive. Hydrogen’s outer shell is incomplete and very violently reactive.
Exam tip: Learn how to relate reactivity to the numbers of electrons in outer shells. This is made more obvious when the scientists show the students the Alkali Metals; Lithium, Sodium and Potassium, reacting with water.
Exam Questions:
∙ Explain with reference to the number of electrons in the outer shell and the increasing size of the atoms why Potassium is more reactive than Sodium.
Bonding Introduction
Compounds are substances in which atoms of two, or more, elements are not just mixed together but chemically combined. This is known as Bonding.
Chemical reactions between elements involve either the giving and taking, or sharing, of electrons in the highest occupied energy levels of atoms.
 
Ionic Bonding
Atoms lose or gain electrons to attain a complete outer shell of electrons.
An ionic bond is formed when electrons are lost and gained by two or more atoms.
When atoms lose electrons they become positive ions
When atoms gain electrons they become negative ions
Ionic bonds are formed between metals and non - metals.
Covalent Bonding
When non-metals react together both atoms need to gain electrons to obtain a full shell of electrons.
The atoms are held together by shared pairs of electrons.
The shared pair of electrons is a covalent bond.
Methane is formed from one carbon atom and four hydrogen atoms.
Each carbon has four outer electrons and each hydrogen atom has 1 outer electron.
Sharing gives both types of atom full outer shells.
Metallic Bonding
In metals, positive metal ions are held together by electron clouds. This is known as metallic bonding.
These electrons are free to move through the structure, this is why metals conduct electricity.reaction mass
 
This can explain the change in melting points as you go down group I.

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