CHEMISTRY · Stage 8 · Chapter 7: Inside Atoms
Chemistry 7.6 Chapter 7 Review: Inside Atoms
5 min read 5 parts Lesson 6 of 6
Lesson summary
7.6 Chapter 7 Review: Inside Atoms — Alhussan International Academy — Chemistry (Stages 7–9) notes: Revise atomic structure, atomic and mass numbers, isotopes and the development of atomic models.Nucleus — it contains protons (charge +1, mass 1) and neutrons (charge 0, mass 1).El…
- Neutral atom
- Atomic number
- Relative atomic mass
- Improving models
- Most particles pass through
- Some are deflected
Part 1 of 5Structure of the atom
- Nucleus — it contains protons (charge +1, mass 1) and neutrons (charge 0, mass 1).
- Electrons — they have charge -1 and negligible mass, and are arranged in shells around the nucleus.
- Neutral atom — it has equal numbers of protons and electrons.
- Shells — the first shell holds 2 electrons and the next two hold up to 8.
- Outer electrons decide chemical properties.
- Models — analogies such as eggs, fruit and nuts can be used to model atoms, for example beryllium with 4 protons, 5 neutrons and 4 electrons has 9 nucleons.
Part 2 of 5Numbers, isotopes and ions
1Atomic number
= the number of protons.
2Mass number1 point
= protons + neutrons.
- Neutrons = mass number - atomic number.
3Isotopes
— they have the same atomic number but different mass numbers.
4Ions2 points
— they form when atoms gain or lose electrons.
- Na+ has 11 protons and 10 electrons.
- O2- has 8 protons and 10 electrons.
5Relative atomic mass1 point
= the weighted average mass of the isotopes.
- Chlorine's value is 35.5 because it is a mixture of chlorine-35 and chlorine-37 in the ratio of their abundance.
Part 3 of 5History of the atom
| Date | Scientist | Contribution |
|---|---|---|
| 1803 | Dalton | Solid indivisible atoms |
| 1897 | Thomson | Discovered the electron; plum pudding model |
| 1909 to 1911 | Rutherford, Geiger, Marsden | Gold foil experiment; nuclear model |
| 1913 | Bohr | Electrons in shells |
| 1932 | Chadwick | Discovered the neutron |
- Improving models — each step came from new experimental evidence, so models change when evidence does not fit.
Part 4 of 5Gold foil observations
- Most particles pass throughthe atom is mostly empty space.
- Some are deflectedthe nucleus is positive and repels the positive alpha particles.
- A few reboundthe nucleus is dense and holds most of the mass.
- Why Rutherford's model is betterit explains the gold foil results, which Thomson's model cannot.
Part 5 of 5Forces in the atom
- Attraction and repulsionopposite charges attract and like charges repel.
- Electronsthey are held by attraction to the nucleus, and outer electrons are held more weakly so they are lost or shared easily.
- Nucleusit is held together by the strong nuclear force.
- Periodic tablethe number of protons orders the elements, and the number of outer electrons decides group properties and reactivity.
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