Overview
This lecture explains the structure of atoms, focusing on calculating numbers of subatomic particles and drawing electron configurations for potassium and argon.
Subatomic Particles in Atoms
- Atoms contain protons, neutrons, and electrons.
- The atomic number equals the number of protons in an atom.
- Potassium (K) has an atomic number of 19, so 19 protons.
- Argon (Ar) has an atomic number of 18, so 18 protons.
- In a neutral atom, the number of electrons equals the number of protons.
- Potassium has 19 electrons; argon has 18 electrons.
- The mass number equals the total of protons plus neutrons.
- Number of neutrons = Mass number − Number of protons.
- Potassium: 39 (mass number) − 19 (protons) = 20 neutrons.
- Argon: 40 (mass number) − 18 (protons) = 22 neutrons.
Electron Configuration and Diagrams
- The first electron shell holds up to 2 electrons.
- The second and third shells each hold up to 8 electrons.
- Potassium’s electron arrangement: 2 electrons (1st shell), 8 (2nd), 8 (3rd), 1 (4th).
- Argon’s electron arrangement: 2 (1st), 8 (2nd), 8 (3rd).
Key Terms & Definitions
- Atomic Number — Number of protons in an atom.
- Mass Number — Sum of protons and neutrons in an atom.
- Electron Configuration — Distribution of electrons among the atom's shells.
- Neutron — Neutral subatomic particle in the nucleus.
- Proton — Positively charged subatomic particle in the nucleus.
- Electron — Negatively charged subatomic particle in shells around the nucleus.
Action Items / Next Steps
- Complete a table summarizing protons, neutrons, and electrons for potassium and argon.
- Practice drawing dot and cross diagrams for K and Ar electron configurations.