2.1.1 Atomic structure and isotopes
Definitions
| Term | Definition |
|---|---|
| Isotopes | Atoms of the same element with the same number of protons and electrons and different numbers of neutrons and different masses. |
| Proton number / atomic number | The number of protons in the nucleus of an atom. |
| Nucleon number / mass number | The number of protons and neutrons in the nucleus of an atom. |
| Relative isotopic mass / | The mass of an isotope of an element compared to 1/12th of the mass of an carbon-12 atom. |
| Relative atomic mass / \(A_{r}\) / \(A_{R}\) | The weighted mean mass of an atom of an element compared to 1/12 of the mass of an atom of carbon-12. |
| Cation | A positively charged ion with fewer electrons than protons. |
| Anion | A negatively charged ion with more electrons than protons. |
Concepts
Properties of isotopes
- Same chemical reactions
- Same electron configuration & the same number of protons
- Number of neutrons has no effect on reactions of an element
- Small differences in physical properties
- Higher mass isotopes = higher melting and boiling point + higher density
Mass and charge of sub-atomic particles
| Particle | Relative charge | Relative mass |
|---|---|---|
| Proton / p+ | 1+ | 1 |
| Neutron / n | 0 | 1 |
| Electron / e- | 1- | 1/1836 |
Determining relative atomic mass and relative isotopic mass (for ions with single charges)
- Mass spectrometer
- Records abundance of ions of different isotopes and their mass-to-charge ratio (m/z ratio)
- Value of relative isotopic mass can be worked out from m/z ratio and hence relative atomic mass