C2 1: Structures and Bonding.

A quick mind jolt to start you off when revising.

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The Nucleus:- The centre of the atom and made up of Protons and Neutrons.

Electrons orbit the nucleus.


  • PROTON +1.
  • NEUTRON 0.
  • ELECTRON -1.

Although Protons and Electrons are charged particles the atom has NO OVERALL CHARGE because there is the same number of Protons and Electrons .

The ATOMIC NUMBER shows you how many Protons and Electrons are in an atom.

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Arrangement of electrons.

Each electron in an atom is in an ENERGY LEVEL or SHELL. The inner shell is always filled with electrons first.Each shell can only hold a specific amount of electrons. For GCSE, you only need to know the first 4 shells:

  • Shell 1 : 2.
  • Shell 2: 8.
  • Shell 3: 8.
  • Shell 4: 18.

This can be writen out as 2,8,8,18.

EXAMPLE: A sodium atom has 11 Electrons. What is it's electronic structure?

* Elements in the same group will always have the same ammount of Electrons in the outer shell. For example, all elements in group 8 would have 8 electrons in their outer shell... SIMPLE :).

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Ionic Bonding.

Used when bonding a metal and a non metal, Chemical bonding takes place when an element wants to become STABLE (have a full outer shell). To do this, an atom must either GAIN or LOSE an electron. This process will create an ION of the element you began with.

Eg. Making Sodium Chloride.

  • Sodium is in Group 1 Chlorine is in Group 7
  • To get a full outer shell, the sodium atom wants to LOSE an electron and the Chlorine atom wants to GAIN an electron.

What happens? Na ----------> Loses an atom and gives it to Cl ---------> becomes Na+.

Cl -----------> Receives an atom from Na ----------> becomes Cl-.

REMEMBER: when an atom LOSES an electron it becomes POSITIVELY CHARGED. When an atom GAINS an electron it will become NEGATIVELY CHARGED.

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Covalent Bonding- when two NON METALS bond.

To become stable, non metals will SHARE electrons with each other.

Eg: creating water. As you can see from the diagram below, ONE oxygen atom will bond with TWO hydrogen atoms. All three atoms now have complete outer shells and create the formula H2O. Bonding in water. Two hydrogen atoms each share one electron, and an oxygen atom shares two electrons (http://www.bbc.co.uk/schools/gcsebitesize/science/images/diag_water.gif)

Atoms of the same element are also able to bond to create full outer shells.

Eg: CHLORINE. Two Chlorine atoms bond to create Cl2. Bonding in chlorine. Two chlorine atoms each share one electron (http://www.bbc.co.uk/schools/gcsebitesize/science/images/diag_chlorine_2.gif)

Covalent structures are also able to join together to create giant structures called LATTICES.

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Metals join together to create giant structure.

(http://www.btinternet.com/~melee3d/revision/chemistry/images/metallic_bond.png) This structure is packed tightly,layer upon layer. The electrons are DELOCALISED, meaning that they are able to move around freely. This produces a "SEA" of moving electrons.

For this reason, metals are easily able to CONDUCT ELECTRICITY.

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  • What is the atomic number of an element?
  • What are the three particles in an atom?
  • Magnesium has 20 electrons, draw a diagram of the shells.
  • Write the number structure of Chlorine (it has 17 electrons)
  • What happens when an electron is lost?
  • What is Covalent bonding?
  • What does it mean by the term "DELOCALISED ELECTRONS"?
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Georgia Comrie

Hope this helps you :D


Question 3 -Magnesium has 12 electrons, calcium has 20!!!!

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