CHEMISTRY · Stage 7 · Chapter 2: Elements, Compounds and Mixtures
Chemistry 2.1 Elements and the periodic table
5 min read 7 parts Lesson 1 of 13
Lesson summary
2.1 Elements and the periodic table — Alhussan International Academy — Chemistry (Stages 7–9) notes: Define an element and use the layout of the periodic table to find information about elements and predict their properties.Element = a pure substance made of only one type of atom…
- Everything
- Names and symbols
- State at room temperature
- Carbon, hydrogen, oxygen and nitrogen
- Stepped line
- Named groups
Part 1 of 7What an element is
- Element = a pure substance made of only one type of atom, which cannot be split into other substances.
- Each element has its own type of particle and its own properties.
- Oxygen, iron, carbon and gold are elements.
- Everything — every material on Earth, and everything in the Universe, is made from the particles of one or more elements.
- Number — there are 118 known elements, about 90 of them natural and the rest made in laboratories.
- Names and symbols — each has its own name and a one- or two-letter symbol, such as O, Fe, C and Au.
- State at room temperature — most are solids, a few such as hydrogen, oxygen and nitrogen are gases, and only mercury and bromine are liquids.
Part 2 of 7Substances and materials
- Materialsthere are millions of materials and most are mixtures.
- Substancea material with just one type of particle.
- Elements are the special substances that cannot be split into other substances.
Part 3 of 7Uses depend on properties
- Platinum — it is expensive, with 1 kg costing more than 33 000 US dollars in 2020, because its properties give it important uses.
- Surgeons insert platinum stents into narrowed blood vessels to keep them open.
- Catalytic converters in cars contain platinum to turn harmful exhaust gases into less harmful ones.
- Hard drives that store computer data contain platinum.
- South Americans made platinum and gold jewellery about 2000 years ago.
- Iron — many useful metal objects contain iron.
Part 4 of 7Common elements
- Hydrogenthe most common element in the Universe, a non-metal.
- Heliumthe second most common element in the Universe.
- Carbon, hydrogen, oxygen and nitrogenliving things are mainly made of these, and all living things including you are mainly carbon.
- Nitrogenthe most common element in the Earth's atmosphere.
Part 5 of 7How the table is organised
- Periodic table = a table that lists all the elements in order of increasing atomic number and groups together elements with similar properties.
- Periods — the rows.
- Groups — the columns, and elements in the same group have similar properties because their atoms have the same number of outer electrons.
- Stepped line — it splits the elements into metals on the left and non-metals on the right.
- Properties of metals and non-metals are studied in Chapter 3.
- Named groups — Group 1 is the alkali metals, Group 7 the halogens and Group 0 the noble gases.
- Transition metals — the block in the middle contains iron, copper and zinc.
- Hydrogen — it sits at the top on its own because it has unique properties and is a non-metal.
Part 6 of 7Information from the table
- Each box shows the symbol, name, atomic number and often the relative atomic mass.
- Sodium shows Na, atomic number 11 and relative atomic mass 23.
- The atomic number is the number of protons.
| Region | Typical properties |
|---|---|
| Metals | Shiny, conduct electricity and heat, malleable, usually solid |
| Non-metals | Dull when solid, poor conductors, brittle if solid |
| Noble gases | Unreactive gases |
Part 7 of 7Patterns you can predict
- Across a period — elements change gradually from metals to non-metals.
- Silicon lies close to the dividing line, has properties of both and is a semiconductor used in computer chips.
- Down Group 1 — the metals become softer and more reactive, so potassium is more reactive than lithium and rubidium reacts violently with water.
- Down Group 7 — the halogens become darker in colour and less reactive.
- Prediction — find the group of an unfamiliar element and use the pattern of its neighbours.
- Sodium — it is in Group 1, so it is a soft, reactive metal that reacts with water.
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