GCSE Chemistry unit 1

1. L.O: To know that elements can react to form
compounds, and that compounds are formed
when electrons are shared or transferred
between atoms. To know that the atoms in a
molecule are held together by covalent bonds.
Thursday, 07 April 2016

2. • What do each of these pictures represent (e.g: elements,
mixtures etc…)
• Click on the boxes to see the labels…

3. • When different elements react, atoms form chemical
bonds with other atoms to form compounds.
• It's usually difficult to separate the two original elements
out again.
• Making bonds involves atoms giving away, taking or
sharing electrons
• If the different atoms aren't bonded together then it's not
a compound — it's a mixture

4. • The properties of a compound are totally different from
the properties of the original elements.

5. • Compounds can be small molecules or great big
structures called lattices (when I say big I'm talking in
atomic terms).

6. • A compound which is formed from a metal and a non-
metal consists of ions.
• Ions are charged particles.
• They are made when atoms lose or gain electrons.
• Metal atoms lose electrons to form positive ions and
non-metal atoms gain electrons to form negative ions.
Metal atoms form positive ions
A sodium atom has 11 protons and 11 electrons. Protons have a relative
charge of +1 and electrons have a relative charge of -1, so the atom has no
overall charge.
If a sodium atom loses an electron it will only have 10 electrons, but it will
still have 11 protons. So the sodium will have an overall charge of +1, and is
said to be a positively charged ion.
Non-metal atoms form negative ions
A chlorine atom has 17 protons and 17 electrons, so has no overall charge.
If a chlorine atom gains an electron it will have 18 electrons, but it will still
only have 17 protons. So it will have an overall charge of -1, and is said to
be a negatively charged ion.

7. • Ions with opposite charges (positive and negative) are
strongly attracted to each other. This is called ionic
bonding.
EXAMPLE
Sodium (a metal) reacts with chlorine (a non-metal) to form the
compound sodium chloride.
The sodium and chloride ions are oppositely charged and so are
attracted to each other. This is ionic bonding, and results in the
formation of the stable compound sodium chloride.

8. • A compound formed from non-metals consists of molecules.
• Each atom shares an electron with another atom — this is called
a covalent bond.
• Each atom has to make enough covalent bonds to fill up its outer
shell.
• Both the hydrogen atom and the chlorine atom now have full outer
shells of electrons. This makes the molecule stable.
Hydrogen and chlorine (both non-metals) react together and share an
electron to form a molecule of hydrogen chloride. The molecule is
made up of two different types of atom, so it's a compound.

9. A formula shows what atoms are in a
compound.
• Carbon dioxide is a compound formed from a
chemical reaction between carbon and oxygen. It
contains one carbon atom and two oxygen
atoms, so the formula is CO2.
• The formula of sulfuric acid is H2SO4. So, each
molecule contains two hydrogen atoms, one
sulfur atom and four oxygen atoms.
• There might be brackets in a formula. For
example, calcium hydroxide is Ca(OH)2. The little
number outside the bracket applies to everything
inside the brackets. So in Ca(OH)2 there is one
calcium atom, two oxygen atoms and two

10. Answer the following questions…

11. 1. What is an ion?
2. Do metal atoms form positive ions or negative ions?
3. Do non-metal atoms form positive ions or negative
ions?
4. If a compound is formed from a metal and a non-metal,
what type of bonding will be present in the compound?
5. What type of bonding holds the atoms in a molecule
together?

12. 1. The formula of carbon monoxide is CO. What atoms are in a
molecule of carbon monoxide?
2. The formula of nitric acid is HNO3. What atoms are in a molecule
of nitric acid?
3. Look at diagrams A, B, C and D (above). Which one shows a
compound?
4. Will bromine form positive or negative ions?
5. Will potassium lose or gain electrons to form ions?
6. Will lithium form positive or negative ions?
7. Will oxygen lose or gain electrons to form ions?
8. Magnesium oxide is made from the reaction between magnesium
and oxygen. What type of bonding exists in magnesium oxide?
9. Sulfur dioxide is made from the reaction between sulfur and
oxygen. What type of bonding exists in sulfur dioxide?

13. ANSWERS – APPLICATION
1. One carbon atom and one oxygen atom.
2. One hydrogen atom, one nitrogen atom
and three oxygen atoms
3. D is a compound because it contains
atoms of different elements chemically
joined together. A and C only contain
atoms of one element, so can't be
compounds. B contains atoms of different
elements, but there are no bonds
between the atoms.
4. Negative ions.
5. Lose electrons.
6. Positive ions.
7. Gain electrons.
8. Ionic bonding – Magnesium is a metal
and oxygen is a non-metal, so the
bonding in magnesium oxide is ionic
bonding.
9. Covalent bonding. Sulfur and oxygen are
both non-metals, so the bonding in sulfur
ANSWERS – FACT
RECALL
1. An ion is a charged
particle
2. Positive ions.
3. Negative ions.
4. Ionic bonding.
5. Covalent bonding.

14. • Write down the definitions
for the keywords on the
worksheet and identify the
compounds, elements, and
mixtures.
• You can use a textbook and
the internet to work out the
ones you don’t know.
• Due in: Next lesson