Elements, compounds and mixtures, reading a formula, and writing balanced symbol equations.
What you will learn
- Tell an element, a compound and a mixture apart
- Count the atoms in a formula, brackets included
- Balance a symbol equation
Elements, compounds, mixtures
- An element has only one type of atom: Fe, O2, S8. About 100 are known, each with a symbol in the periodic table.
- A compound has two or more elements chemically combined in fixed proportions: H2O, NaCl. Only a chemical reaction can split it up.
- A mixture has two or more substances not chemically joined: air, sea water. Physical methods separate it.
Everyday mixtures include air, sea water, salty water, ink, orange juice and alloys such as brass (an alloy is a mixture of a metal with other elements: brass is copper and zinc mixed, not bonded). A single substance, such as oxygen, copper, methane or carbon dioxide, is an element or a compound, not a mixture: a pure substance is a single element or compound with nothing else mixed in.
The rest of this lesson and its 7 practice questions are locked.
In this lesson
- Elements, compounds, mixtures
- Reading a formula
- Balancing equations
- Word equations
- Try it: Count the atoms
7 practice questions, marked as you go; about 20 minutes in all.
Key terms
Element, Compound, Mixture, Alloy, Pure substance
In this unit: Atomic structure and the periodic table
Atoms, formulae and equations, separating mixtures, the model of the atom, isotopes, electrons in shells and the groups of the periodic table.
- Atoms, elements, compounds and equations
- Separating mixtures
- The model of the atom
- Isotopes and electronic structure
- The periodic table
- Groups 0, 1 and 7
- The transition metals