CompoundsL.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.

Monday 1 May 2023

Starter• What do each of these pictures represent (e.g:

elements, mixtures etc…)• Click on the boxes to see the labels…

An atom?

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?

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What are compounds?• 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 

Properties of compounds…• The properties of a compound are totally different

from the properties of the original elements.EXAMPLEIf iron (a lustrous magnetic metal) and sulfur (a nice yellow powder) react, the compound formed (iron sulfide) is a dull grey solid lump, and doesn't behave anything like either iron or sulfur.

Lattices and Molecules• Compounds can be small molecules or great big

structures called lattices (when I say big I'm talking in atomic terms).

WATER MOLECUL

E

PART OF A SODIUM

CHLORIDE LATTICE

Ions• 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 ionsA 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 ionsA 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.

Ionic Bonding• Ions with opposite charges (positive and negative)

are strongly attracted to each other. This is called ionic bonding.

EXAMPLESodium (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.

Covalent Bonding• 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.

FormulaeA 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 hydrogen atoms.

Answer the following questions…Questions

Fact Recall1. 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?

Application1. 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?

ANSWERS – APPLICATION1. One carbon atom and one oxygen

atom.2. One hydrogen atom, one nitrogen

atom and three oxygen atoms3. 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 dioxide is covalent bonding

ANSWERS – FACT RECALL

1. An ion is a charged particle

2. Positive ions.3. Negative ions.4. Ionic bonding.

5. Covalent bonding.

Homework• 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