Basic 9 · Science · Materials
Binary Chemical Compounds
In this topic you will identify binary chemical compounds by name, discuss their uses and explain how they are formed.
By the end of these notes you should be able to:
- Name binary chemical compounds
- Discuss the uses of binary compounds
- Explain how binary compounds form
What you already know
- Elements and compounds
- The periodic table
Copy everything that has a blue line on its left into your notebook. The other parts are for reading.
Lesson 1
- Strand
- Diversity Of Matter
- Sub-strand
- Materials
- Indicator
- B9.1.1.1.1 – Identify by name binary chemical compounds and discuss their uses
Introduction
Common salt is made of a soft metal and a poisonous gas. Together, they form something you eat every day. That is the power of a chemical compound.
1. What Is a Binary Compound?
Binary compound: A compound made up of two elements.
| Compound | Formula | Elements |
|---|---|---|
| sodium chloride | NaCl | sodium, chlorine |
| water | H₂O | hydrogen, oxygen |
| carbon dioxide | CO₂ | carbon, oxygen |
| hydrogen chloride | HCl | hydrogen, chlorine |
| calcium oxide | CaO | calcium, oxygen |
| ammonia | NH₃ | nitrogen, hydrogen |
| iron(III) oxide | Fe₂O₃ | iron, oxygen |
| aluminium oxide | Al₂O₃ | aluminium, oxygen |
2. Naming Rules
- Write the name of the metal, or the less non-metallic element, first.
- Change the ending of the second element to "-ide".
- Use prefixes for two non-metals, such as di- or tri-.
- Use Roman numerals for metals with several charges.
| Elements | Compound |
|---|---|
| sodium + chlorine | sodium chloride |
| magnesium + oxygen | magnesium oxide |
| iron + sulfur | iron(II) sulfide |
| carbon + oxygen (1:1) | carbon monoxide |
| carbon + oxygen (1:2) | carbon dioxide |
| sulfur + oxygen (1:3) | sulfur trioxide |
The subscript in a formula shows the number of atoms. In CO₂, there is one carbon atom and two oxygen atoms. Some common names, such as water and ammonia, do not follow these rules, but they are in general use.
3. Reading Formulae
Counting atoms
How many atoms of each element are in Al₂O₃?
- The subscript 2 follows Al.
- The subscript 3 follows O.
Answer: 2 aluminium atoms and 3 oxygen atoms
4. Carbon Monoxide and Carbon Dioxide
A small difference in a formula can mean a big difference in properties. CO₂ is breathed out, and plants use it. CO, or carbon monoxide, is poisonous. It is made when fuels burn with too little oxygen, such as a charcoal pot in a closed room. It has no smell, and people have died from it in their sleep. Never burn charcoal or run a generator in a closed room.
New words
- binary compound
- A compound of two elements.
- formula
- A symbol form of a compound.
- subscript
- A small number showing atoms.
- -ide
- The ending for a binary compound's second element.
Summary
- Binary compounds contain two elements.
- The second element's name ends in -ide.
- Formulae show the number of atoms.
Class activity: Compound Cards
- Match compound names with formulae.
- Name the elements.
- Check with a chart.
You need: Table salt sample, Water in a beaker, Printed particle-model cards
Exercises
Answer in your exercise book first, then check your answers.
1. NaCl is…
- A. sodium chloride
- B. water
- C. ammonia
- D. carbon dioxide
Show answer
Answer: sodium chlorideName.2. Which is a binary compound?
- A. MgO
- B. H₂SO₄
- C. NaOH
- D. CaCO₃
Show answer
Answer: MgOTwo elements.3. H₂O has two hydrogen atoms.
- A. True
- B. False
Show answer
Answer: TrueSubscript.4. Magnesium and oxygen form magnesium ______.
Show answer
Answer: oxideNaming.5. Name the compound with formula CaO.
Show answer
Answer: Calcium oxideNaming.6. Why is it dangerous to burn charcoal in a closed room?
Show answer
Answer: It produces carbon monoxide, a poisonous gas with no smell.Safety.
Lesson 2
- Strand
- Diversity Of Matter
- Sub-strand
- Materials
- Indicator
- B9.1.1.1.1 – Identify by name binary chemical compounds and discuss their uses
Introduction
Binary compounds are all around you, in your food, your home, your farm and your body.
1. Everyday Uses
| Compound | Uses |
|---|---|
| water (H₂O) | life, cooking, solvent |
| sodium chloride (NaCl) | food seasoning, preservation |
| carbon dioxide (CO₂) | fizzy drinks, fire extinguishers, photosynthesis |
| calcium oxide (CaO) | cement, reducing soil acidity |
| ammonia (NH₃) | fertilisers, cleaning |
| hydrogen chloride (HCl) | dissolved in water, it is used in industry |
| aluminium oxide (Al₂O₃) | source of aluminium |
| iron oxide | source of iron, paint pigment |
2. Binary Compounds in Ghana
Ghana has important resources that contain binary compounds. Bauxite, mined at Nyinahin and Awaso, contains aluminium oxide. It is processed to give aluminium. Salt is obtained at Ada and Keta by evaporating sea water. Salt was an important trade item for centuries, and it has long been used to preserve fish. Limestone from places such as Nauli in the Western Region is used for making cement, and heating limestone gives calcium oxide, also called quicklime.
3. In the Body
Water makes up over half of the body's mass. Salts dissolved in the blood help nerves and muscles to work. Stomach acid contains hydrochloric acid, a solution of HCl, which helps to digest food. Doctors use oxygen compounds in medicine. Iron oxide gives rust its colour and is the cause of red soil, and the iron in blood is needed to carry oxygen, in a much more complex compound.
4. Harmful Effects
| Compound | Danger |
|---|---|
| carbon monoxide | poisonous gas |
| sulfur dioxide | causes acid rain |
| nitrogen dioxide | air pollution |
| hydrogen sulfide | poisonous, smells of rotten eggs |
Compounds can be useful in one setting, and harmful in another. Too much salt raises blood pressure. Too much carbon dioxide adds to global warming. Sulfur dioxide from burning fuel can form acid rain. Understanding compounds helps us to use them wisely.
New words
- bauxite
- The ore of aluminium.
- quicklime
- Calcium oxide.
- preservative
- A substance that keeps food from going bad.
- acid rain
- Rain polluted by acidic gases.
Summary
- Binary compounds have many uses in daily life.
- Ghana has bauxite, salt and limestone.
- Some compounds are harmful.
Class activity: Compound Hunt
- Find items at home containing binary compounds.
- List their uses.
- Report to the class.
You need: Table salt sample, Water in a beaker, Printed particle-model cards
Exercises
Answer in your exercise book first, then check your answers.
1. Salt is used to…
- A. preserve food
- B. make paper
- C. light a bulb
- D. dye hair
Show answer
Answer: preserve foodUse.2. Bauxite contains…
- A. aluminium oxide
- B. sodium chloride
- C. ammonia
- D. water only
Show answer
Answer: aluminium oxideOre.3. Sulfur dioxide can cause acid rain.
- A. True
- B. False
Show answer
Answer: TruePollution.4. Calcium oxide is also called ______.
Show answer
Answer: quicklimeTerm.5. Give two uses of carbon dioxide.
Show answer
Answer: Fizzy drinks and fire extinguishers.Any two.6. How can salt be both useful and harmful?
Show answer
Answer: It flavours and preserves food, but too much raises blood pressure.Balance.
Lesson 3
- Strand
- Diversity Of Matter
- Sub-strand
- Materials
- Indicator
- B9.1.1.1.2 – Discuss the formation of binary chemical compounds
Introduction
Why do sodium and chlorine join so readily? The answer lies in the outer electrons of their atoms.
1. Atoms and Electrons
Atoms contain protons, neutrons and electrons. Electrons are arranged in shells. Atoms are most stable when their outer shell is full, as in the noble gases such as neon and argon. Atoms that do not have full outer shells react with others to become stable. This is the driving force behind most chemical reactions.
| Element | Atomic number | Arrangement |
|---|---|---|
| sodium | 11 | 2, 8, 1 |
| magnesium | 12 | 2, 8, 2 |
| chlorine | 17 | 2, 8, 7 |
| oxygen | 8 | 2, 6 |
| neon | 10 | 2, 8 |
2. Formation by Reaction
Forming salt
Write the word and symbol equations for the reaction between sodium and chlorine.
- Word equation: sodium + chlorine → sodium chloride.
- Symbol equation: 2Na + Cl₂ → 2NaCl.
Answer: 2Na + Cl₂ → 2NaCl
Forming an oxide
Write the equation for burning magnesium in oxygen.
- Word equation: magnesium + oxygen → magnesium oxide.
- Symbol equation: 2Mg + O₂ → 2MgO.
Answer: 2Mg + O₂ → 2MgO
In a balanced equation, the number of each kind of atom is the same on both sides. Atoms are not lost or created, only rearranged. This is the law of conservation of mass.
3. Observing Reactions
Signs of a chemical reaction include a change of colour, the giving off of gas, a change of temperature and the formation of a new solid. When iron rusts, a brown oxide forms. The product has new properties. Iron is strong and magnetic, but rust is flaky and weak. Compounds differ greatly from the elements that form them. Sodium is a reactive metal and chlorine a poisonous gas, but sodium chloride is a safe food seasoning.
4. Combining Power
Valency is the combining power of an atom. Sodium has a valency of 1, magnesium 2, oxygen 2 and chlorine 1. We can use this to work out formulae. Since magnesium and oxygen both have a valency of 2, the formula is MgO. Aluminium (3) and oxygen (2) need Al₂O₃, as 2 × 3 = 3 × 2.
Safety: Burning magnesium gives out very bright light. Do not look directly at it, and let only your teacher demonstrate it.
New words
- electron
- A negative particle in an atom.
- shell
- An energy level around a nucleus.
- valency
- The combining power of an atom.
- balanced equation
- An equation with equal atoms on both sides.
Summary
- Atoms react to get full outer shells.
- Equations show how compounds form.
- Compounds have new properties.
Class activity: Balance It
- Use counters as atoms.
- Model 2Mg + O₂ → 2MgO.
- Check that atoms are balanced.
You need: Coloured bottle tops, Wooden sticks, Printed particle-model cards
Exercises
Answer in your exercise book first, then check your answers.
1. Sodium's electron arrangement is…
- A. 2, 8, 1
- B. 2, 8
- C. 2, 6
- D. 2, 8, 7
Show answer
Answer: 2, 8, 1Electrons.2. Which formula is correct?
- A. MgO
- B. Mg₂O
- C. MgO₂
- D. Mg₂O₃
Show answer
Answer: MgOValency.3. Atoms are rearranged in a reaction.
- A. True
- B. False
Show answer
Answer: TrueConservation.4. The combining power of an atom is its ______.
Show answer
Answer: valencyTerm.5. Give two signs of a chemical reaction.
Show answer
Answer: A colour change and a gas given off.Any two.6. Work out the formula of aluminium oxide.
Show answer
Answer: Al₂O₃, as 2 × 3 = 3 × 2.Valency.
Homework
- Write the names and formulae of ten binary compounds.