1.1.1Atomic Structure and the Periodic Table
Elements — AQA GCSE Combined Science Trilogy 8464 - Chemistry Revision Notes & Topical Questions
5 min read 8 parts Lesson 2 of 17
Section 1 of 8What an element is
One type of atom
- One type of atom An element is a substance made of only one type of atom.
- It cannot be broken down into anything simpler by chemical reactions.
Symbols
- Symbols Each element has a symbol of one or two letters, the first a capital: C, Na, Fe.
- Some symbols come from Latin names, for example Na from natrium and Fe from ferrum.
- The symbol is an international code, so scientists in every country can read the same formula.
About 100 elements
- About 100 elements Every substance is made from elements, either on their own or combined.
- Around 90 occur naturally and the rest have been made artificially.
Section 2 of 8Atoms of an element
Atoms
Atomic number
- Atomic number The number of protons in the nucleus; it identifies the element.
Neutral
- Neutral Atoms have equal numbers of protons and electrons, so no overall charge.
- If an atom gains or loses electrons it becomes an ion with an overall charge, but it is still the same element.
Mass number
- Mass number The total number of protons plus neutrons.
Isotopes
- Isotopes Atoms of the same element with different numbers of neutrons, so they have the same atomic number but different mass numbers.
Section 3 of 8Elements on the periodic table
| Feature | Meaning |
|---|---|
| Groups (columns) | Elements with the same number of outer electrons and similar properties |
| Periods (rows) | Elements with the same number of occupied electron shells |
| Order | Increasing atomic number from left to right |
| Metals | To the left and centre, forming positive ions |
| Non-metals | To the right, forming negative ions or sharing electrons |
Section 4 of 8Properties of metals and non-metals
| Property | Metals | Non-metals |
|---|---|---|
| Appearance | Shiny | Dull when solid |
| Conduction | Good conductors of heat and electricity | Poor conductors (graphite is an exception) |
| Strength | Strong, malleable and ductile | Brittle when solid |
| Oxides | Basic | Acidic |
Section 5 of 8Element or not?
1Look at the particles
- Look at the particles If all atoms are identical, it is an element.
2Molecules can be elements
- Molecules can be elements O2 and N2 have two atoms but are still single elements, because both atoms are the same type.
3Different atoms joined
- Different atoms joined Then it is a compound, with a formula such as CO2 or H2O.
Section 6 of 8Reading an element's entry
1
Find the element's box on the periodic table and read its symbol, such as Na for sodium.
2
Read the atomic number, which is 11 for sodium, so a sodium atom has 11 protons and 11 electrons.
3
Read the relative atomic mass, about 23 for sodium, and subtract the atomic number to find 12 neutrons.
4
Write the electron arrangement 2,8,1, which shows one outer electron, so sodium is in Group 1.
5
Count the occupied shells, which is three, so sodium is in Period 3.
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Element | A substance made of only one type of atom. |
| Atomic number | The number of protons in the nucleus of an atom. |
| Mass number | The total number of protons and neutrons in an atom. |
| Group | A vertical column of the periodic table. |
| Period | A horizontal row of the periodic table. |
| Isotope | Atoms of the same element with the same number of protons but different numbers of neutrons. |
Section 8 of 8Exam technique
1
Saying that a molecule such as O2 cannot be an element because it has two atoms.
2
Using lower-case first letters in symbols, for example 'na' for sodium.
3
Confusing atomic number with mass number.
4
Describing a group as a row.
5
Thinking elements in the same period share similar properties; this applies to groups.
6
Writing the mass number below the atomic number; the larger number, the mass number, is written on top.
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