Summary
Atoms consist of a nucleus containing protons and neutrons, with electrons orbiting in shells. The atomic radius is the size of an atom, influenced by the number of electrons and effective nuclear charge.
- Atom — the smallest unit of an element, consisting of a nucleus and electrons. Example: Hydrogen atom
- Proton — a positively charged particle in the nucleus. Example: Found in the nucleus of a helium atom
- Neutron — a neutral particle in the nucleus. Example: Found in the nucleus of a carbon atom
- Electron — a negatively charged particle orbiting the nucleus. Example: Found in the outer shell of a sodium atom
- Atomic Radius — half the distance between the nuclei of two adjacent atoms. Example: The atomic radius of chlorine is smaller than that of sodium
- Ionic Radius — the size of an ion, affected by electron removal or addition. Example: The ionic radius of Na+ is smaller than that of Na
Exam Tips
Key Definitions to Remember
- Atomic number: Number of protons in the nucleus
- Mass number: Total number of protons and neutrons
- Isotopes: Atoms with the same atomic number but different mass numbers
Common Confusions
- Confusing atomic radius with ionic radius
- Misunderstanding the effect of nuclear charge on atomic size
Typical Exam Questions
- What is the atomic number of an element? The number of protons in its nucleus
- How does atomic radius change across a period? It decreases due to increased nuclear charge
- What is the difference between atomic and ionic radius? Atomic radius is for neutral atoms; ionic radius is for charged ions
What Examiners Usually Test
- Understanding of atomic and ionic radii trends in the periodic table
- Ability to calculate the number of neutrons from mass and atomic numbers
- Knowledge of how atomic structure relates to the periodic table