Topic 1 - Atoms!

Charges, ions, covalant bonding, ionic bonding and balancing equations explained simply.

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  • Created by: Elsie_
  • Created on: 02-06-12 17:28


The atomic number [the number at the bottom when listed in a periodic table] tells us the number of Protons in the nucleus.

The atomic mass [the number at the top] tells us the number of Protons AND Neutrons in the nucleus.

So... to find the number of neutrons we take away the atomic number [protons] from the atomic mass [protons and neutrons]

Protons have a charge of +1

Neutrons have no charge

Electrons [the things that occupy the atoms shells] have a charge of -1

Atoms have the same number of electrons and protons so have no charge

So... if an atom loses electrons it becomes positively charged and if it gains it becomes negatively charged.

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What is an ion?

Ions are atoms that have lost or gained electrons to give them a positive or negative charge.

There are two types of ions:

  • Metal ions - atoms that have lost negative electrons to give them an overall positive charge.
  • Non metal ions - atoms that have gained negative electrons to give them an overall negative charge.

Why do they do this?

Because all atoms want a full outer shell of electrons, so they can be stable and happy :)

How do they do this?

Covalent or ionic bonding; explained in my next cards :)

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Covalent bonding

Non metals make Covalent bonds in order to achieve a full outer shell.

They link their shells together so they can share electrons and fill their outer shells.

How many electrons they gain [non metals always gain] depends on what group they are in.

For example: oxygen is in group 6, this means there will be 6 electrons in it's outer shell, to make a full outer shell it wants 8 electrons.

It does this by making a covalent bond with another oxygen, they share 2 electrons which is called a double bond.

Because they are joined together we call it O2.

Non metals that have reacted together are called molecules. O2 is a molecule.

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Ionic bonding!

Metals and non metals react together to achive a full outer shell - this is Ionic bonding.

Rule: Metals always lose electrons when they react with non metals.


Na [11 electrons; 1 in the outer shell] + Cl [17 electrons 7 in the outer shell] =

Na+ [with 10 electrons; 8 in the outer shell] + Cl- [18 electrons; 8 in the outer shell]

The chemical equation for this reaction would be:

Na + Cl = NaCl [we don't write the charges because they cancel each other out]

A compound is two or more atoms chemically bonded together

NaCl is a compound.

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Balancing equations!

A good way to remember is that Gasses are a bit like Girls, they always travel around in pairs.

So, We have the gasses H2 + O2 and we want to make H2O [water]

If we wrote it like this: H2 + O2 = H2O it wouldn't make sense because there is one less oxygen at the end. Unfortunately we can't just write H2O2 as that is not how chemistry works. We have to balance it!

We balance equations by putting big numbers at the front of the compounds/molecules until the equation has the same number of atoms on each side. Just play around with the numbers until you get it right.

4H2 + 2O2 = 4H2O How do we know this is right?

[4x2=8] 8H + [2x2=4] 4O = [4x2=8] 8H + [4xO] 4O

YAY! it's balanced because we have 8H and 4O on both sides!

Just keep practising until it its easy!

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Thank you! Very helpful :D

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