Summary
Atoms are the basic units of matter, consisting of a nucleus surrounded by electrons in shells. The nucleus contains protons and neutrons, while electrons orbit in defined energy levels.
- Atom — the smallest unit of an element, consisting of protons, neutrons, and electrons. Example: A sodium atom has 11 protons, 11 electrons, and usually 12 neutrons.
- Proton Number (Atomic Number) — the number of protons in the nucleus of an atom. Example: Carbon has a proton number of 6.
- Nucleon Number (Mass Number) — the total number of protons and neutrons in the nucleus. Example: Oxygen has a nucleon number of 16.
- Electron Configuration — the arrangement of electrons in an atom's energy levels. Example: The electron configuration of neon is 2, 8.
- Noble Gases — elements in Group VIII with a full outer electron shell. Example: Helium is a noble gas with a complete outer shell.
Exam Tips
Key Definitions to Remember
- Proton number is the number of protons in an atom's nucleus.
- Nucleon number is the total number of protons and neutrons.
Common Confusions
- Confusing proton number with nucleon number.
- Misunderstanding electron shell capacity.
Typical Exam Questions
- What is the proton number of carbon? Answer: 6
- How many electrons can the second energy level hold? Answer: 8
- What is the electron configuration of sodium? Answer: 2, 8, 1
What Examiners Usually Test
- Understanding of atomic structure and subatomic particles.
- Ability to determine electron configurations.
- Knowledge of periodic table trends and group properties.