CHEMISTRY · Stage 7 · Chapter 2: Elements, Compounds and Mixtures
Chemistry 2.4 Atoms — Elements and Atomic Arrangement
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Lesson summary
2.4 Atoms — Elements and Atomic Arrangement — Alhussan International Academy — Chemistry (Stages 7–9) notes: Define atom and element, describe how atoms are arranged in elements, and explain that the properties of an element are the properties of many atoms together.Atom = the sm…
- Own type of atom
- Limitations
- Single atoms
- Giant structures
- Allotropes
- Reading a diagram
Section 1 of 7Atoms
- Atom = the smallest particle of an element that can exist.
- Size
- the diameter of one atom is about 0.000 000 01 cm, so one hundred million atoms side by side stretch one centimetre.
- Pictures
- a special microscope can show the surface of silicon magnified ten million times, and the spheres in it are atoms.
Section 2 of 7Atoms and elements
- Own type of atom
- every element has its own type of atom,
- so all silicon atoms are alike, all platinum atoms are alike and the atoms of each element differ from those of every other element.
- Atoms of different elements differ in mass and in the number of protons.
- There are about 100 elements, so there are about 100 types of atom.
- Element = a substance that is made from one type of atom and cannot be split into other substances.
- Silicon
- it is the main element in a lump of silicon and in the integrated circuits in electronic devices, where its semiconductor properties are useful.
Section 3 of 7Properties of an element
1Many atoms3 points
- the properties of an element are the properties of many atoms together.
- A block of copper of 1 kg contains about 9 000 000 000 000 000 000 000 000 atoms, which together make copper red-brown and shiny.
- A single copper atom is not red-brown or shiny and is not in a solid, liquid or gas state.
2Melting2 points
- in the block the atoms have fixed positions, and at 1084 °C they leave their positions and slide over each other.
- One atom cannot melt, and only many atoms together can.
Section 4 of 7Modelling atoms with toy bricks
- Strengths
- the model shows that every element has its own type of atom and that many atoms may join together.
- Bricks of one colour represent atoms of one element, such as gold, oxygen or nitrogen.
- Limitations
- atoms do not have straight edges and are much smaller than toy bricks.
Section 5 of 7Arrangements of atoms in elements
- Single atoms
- the noble gases such as helium and neon exist as separate atoms because their atoms are stable on their own.
- Molecules
- some non-metal elements have atoms joined together.
- Hydrogen (H2), oxygen (O2), nitrogen (N2) and chlorine (Cl2) have two atoms per molecule.
- Sulfur forms S8 rings and phosphorus forms P4.
- Weak forces between molecules give these elements low melting and boiling points.
- Giant structures
- in metals atoms are packed in regular layers, which explains why metals can be bent and hammered and conduct electricity.
- In diamond and graphite millions of carbon atoms are joined in a giant network.
Section 6 of 7Allotropes
- Allotropes = different structures of the same element.
- Carbon
- diamond and graphite are both pure carbon, but the atoms are arranged differently.
- Diamond is very hard, each carbon atom joined to four others in a strong three-dimensional network, with a very high melting point.
- Graphite is soft and conducts electricity.
Section 7 of 7Particle diagrams
| Diagram | Meaning |
|---|---|
| All identical single circles | Element made of single atoms (for example neon) |
| Identical pairs of joined circles | Element in molecules (for example O2) |
| Different joined circles | Compound |
| Different separate circles | Mixture |
- Reading a diagram
- count the types of circle first, then check whether they are joined or apart.
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