Summary
The nuclear model of an atom describes it as consisting of a central nucleus containing protons and neutrons, with electrons orbiting around it. The Geiger and Marsden experiment provided evidence for this model by showing that alpha particles are deflected by a concentrated positive charge in the nucleus.
- Atom — the basic unit of an element, consisting of protons, neutrons, and electrons. Example: Hydrogen is the simplest atom with one proton and one electron.
- Proton — a positively charged particle found in the nucleus. Example: The hydrogen atom has one proton.
- Neutron — an uncharged particle found in the nucleus. Example: Carbon-12 has six neutrons.
- Electron — a negatively charged particle orbiting the nucleus. Example: In a neutral helium atom, there are two electrons.
- Nucleus — the central part of an atom containing protons and neutrons. Example: The nucleus of a helium atom contains two protons and two neutrons.
- Ion — an atom that has gained or lost electrons, resulting in a net charge. Example: A sodium ion (Na+) forms when a sodium atom loses an electron.
- Nuclear Fission — a reaction where a nucleus splits into smaller nuclei, releasing energy. Example: Uranium-235 undergoing fission in a nuclear reactor.
- Nuclear Fusion — a process where small nuclei combine to form a larger nucleus, releasing energy. Example: Hydrogen nuclei fusing to form helium in the sun.
Exam Tips
Key Definitions to Remember
- Atom: Basic unit of an element made up of protons, neutrons, and electrons.
- Proton: Positively charged particle in the nucleus.
- Neutron: Uncharged particle in the nucleus.
- Electron: Negatively charged particle orbiting the nucleus.
- Ion: Atom with a net charge due to loss or gain of electrons.
- Nuclear Fission: Splitting of a nucleus into smaller parts, releasing energy.
- Nuclear Fusion: Combining of small nuclei to form a larger nucleus, releasing energy.
Common Confusions
- Confusing the roles of protons and electrons in determining an atom's charge.
- Misunderstanding the difference between nuclear fission and fusion.
Typical Exam Questions
- Which particles make up the nucleus? Protons and neutrons
- Which particle orbits around the nucleus? Electron
- An atom of a particular isotope of oxygen (symbol O) contains 8 protons and 9 neutrons. Write down the full symbol of this atom. O
What Examiners Usually Test
- Understanding of the nuclear model and the structure of an atom.
- Ability to explain the Geiger and Marsden experiment and its significance.
- Knowledge of nuclear reactions, including fission and fusion.