Overview
This lecture introduces ions, explaining how atoms gain or lose electrons, and covers key concepts such as cations, anions, electronegativity, ionization energy, electron affinity, and the octet rule.
What Are Ions?
- Ions are atoms that carry a positive or negative charge due to gaining or losing electrons.
- Losing electrons forms positive ions (cations); gaining electrons forms negative ions (anions).
Formation of Ions
- Valence electrons are the outermost electrons and are lost or gained during ion formation.
- The periodic table is organized by atomic number; groups indicate the number of valence electrons.
- Atoms become ions to achieve a stable electron configuration, often satisfying the octet rule (eight valence electrons).
Electronegativity, Ionization Energy, and Electron Affinity
- Electronegativity is an atom's ability to attract electrons; fluorine has the highest electronegativity in period 2.
- Non-metals usually gain electrons (become anions), while metals lose electrons (become cations).
- Ionization energy is the energy needed to remove an electron; lithium has the lowest ionization energy in period 2.
- Electron affinity is the energy released when an atom gains an electron.
The Octet Rule and Stability
- The octet rule states that atoms prefer having eight electrons in their valence shell for stability.
- Noble gases, like neon, are already stable and do not form ions easily.
- Bohr models illustrate how an atom moves from a neutral to an ionized state.
Ion Size Changes
- When atoms gain electrons (anions), their size increases due to electron repulsion.
- When atoms lose electrons (cations), their size decreases due to fewer valence electrons.
Summary of Key Concepts
- Anions: More electrons than protons, negatively charged.
- Cations: More protons than electrons, positively charged.
- Valence electrons: Outermost electrons involved in chemical activity.
- Octet rule: Atoms tend to have eight electrons in their valence shell for stability.
Key Terms & Definitions
- Ion — Atom with a positive or negative charge from electron loss or gain.
- Cation — Positively charged ion with more protons than electrons.
- Anion — Negatively charged ion with more electrons than protons.
- Valence Electrons — Electrons in the outermost shell of an atom.
- Electronegativity — Atom’s ability to attract electrons.
- Ionization Energy — Energy needed to remove an electron.
- Electron Affinity — Energy released when an atom gains an electron.
- Octet Rule — Atoms prefer eight electrons in their valence shell.
Action Items / Next Steps
- Prepare for the next lesson on how the structure of the carbon atom affects bond formation.