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Unit 2: States of matter, atoms and compounds

Compounds And Formulae — HIA International - Grade 6 Revision Notes & Topical Questions

5 min read 9 parts Lesson 8 of 10 1 quiz

📚 HIA International - Grade 6 Hub / Topical Revision
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Lesson summary

2.6 Compounds And Formulae — HIA INTERNATIONAL notes: Explain what a compound is, name compounds and use chemical formulae.Compound — a substance in which two or more different kinds of atom are bonded tightly together.Bonding — the chemical term for atoms joining tightly togethe…

  • Fixed amounts
  • Completely new
  • Separation
  • Metal first
  • Non-metal changed
  • Small number

Section 1 of 9Compounds

Compound
  • Compound a substance in which two or more different kinds of atom are bonded tightly together.
Bonding
  • Bonding the chemical term for atoms joining tightly together.
Fixed amounts
  • Fixed amounts the elements are joined in fixed proportions.
Example
  • Example sodium atoms bonded with chlorine atoms form sodium chloride.

Section 2 of 9Properties of compounds

Completely new
  • Completely new a compound has totally new properties from the elements it contains.
Example
  • Example sodium chloride (common salt) is not like sodium, a reactive metal, or chlorine, a toxic gas.
Separation
  • Separation a compound can only be separated by a chemical reaction, not by filtering.

Section 3 of 9Naming compounds

1Metal first
  • Metal first the name of the metal comes first.
2Non-metal changed
  • Non-metal changed the non-metal name usually changes, so sodium and chlorine make sodium chloride.
3-ide
  • -ide the name often ends in -ide when two elements are combined, such as magnesium oxide.
4-ate
  • -ate the name often ends in -ate when oxygen is also present, such as calcium carbonate and copper sulfate.
5Prefixes
  • "mono" means one and "di" means two, so carbon monoxide has one oxygen and carbon dioxide has two.

Section 4 of 9Particle diagrams

Particle diagrams
Compound
  • Compound if different kinds of atom are bonded together in a particle, the substance is a compound.
Element
  • Element if the atoms in a particle are all the same, such as O2, it is an element.
Molecule
  • Molecule two or more atoms bonded together, in an element or a compound.

Section 5 of 9Chemical formulae

Meaning
  • Meaning a formula contains the symbols of the elements bonded in the compound.
Small number
  • Small number written below and to the right, it shows how many atoms of the element before it.
No number
  • No number there is just one atom of that element.
Bracket
  • Bracket it multiplies everything inside, so Ca(OH)2 has 1 calcium, 2 oxygen and 2 hydrogen atoms.
Care
  • Care avoid confusing C for carbon with Ca for calcium.

Section 6 of 9Examples of formulae

NameFormulaAtoms in a particle
Calcium oxideCaO1 calcium, 1 oxygen
Carbon dioxideCO21 carbon, 2 oxygen
Carbon monoxideCO1 carbon, 1 oxygen
Hydrogen sulfideH2S2 hydrogen, 1 sulfur
Calcium carbonateCaCO31 calcium, 1 carbon, 3 oxygen
Sodium hydroxideNaOH1 sodium, 1 oxygen, 1 hydrogen
WaterH2O2 hydrogen, 1 oxygen

Section 7 of 9Compound or mixture

Compound
  • Compound made of elements chemically joined, and its formula records fixed proportions.
Mixture
  • Mixture not chemically joined, so it can be separated physically.
Examples
  • Examples water is a compound, whereas air is a mixture.
Same elements
  • Same elements carbon and oxygen make both CO and CO2, with different properties.

Section 8 of 9Key terms

TermMeaning
CompoundA substance of two or more different elements chemically joined.
BondingAtoms joining tightly together.
FormulaSymbols and numbers showing which atoms are in a compound and how many.
MoleculeTwo or more atoms bonded together.
ReactantA substance you start with in a chemical reaction.
ProductA new substance made in a chemical reaction.

Section 9 of 9Exam technique

1
Calling NaCl sodium chlorine — the non-metal ending changes to -ide, so it is sodium chloride.
2
Reading the small number as applying to every symbol — it applies only to the symbol before it.
3
Thinking a compound can be separated by filtering — it needs a chemical reaction.
4
Calling O₂ a compound — both atoms are oxygen, so it is an element.

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