Overview
This lecture explains ionic bonds, focusing on how they form between metals and non-metals due to large differences in electronegativity, using sodium and chlorine as examples.
Types of Chemical Bonds
- Three main bond types: covalent (non-polar and polar), ionic, and hydrogen bonds.
- Ionic bonds are attractions between ions of opposite charge.
Basics of Ionic Bonds
- Ionic bonds form when electrons are transferred from one atom to another, resulting in charged ions.
- Opposite charges (positive and negative) attract, creating the ionic bond.
- Typically occur between metals (low electronegativity) and non-metals (high electronegativity) on the periodic table.
Role of Electronegativity
- Electronegativity is an atom’s ability to pull electrons toward itself.
- Increases left to right and bottom to top on the periodic table.
- Large difference in electronegativity between two atoms promotes ionic bond formation.
Formation of Ions: Sodium & Chlorine Example
- Sodium (Na), atomic number 11: 11 protons, 11 electrons, 1 electron in outer shell.
- Chlorine (Cl), atomic number 17: 17 protons, 17 electrons, 7 electrons in outer shell.
- Atoms seek full outer electron shells to be stable.
- Sodium loses 1 electron to become Na⁺ (cation), now 10 electrons and 11 protons.
- Chlorine gains 1 electron to become Cl⁻ (anion), now 18 electrons and 17 protons.
Formation of Sodium Chloride (NaCl)
- Na⁺ and Cl⁻ are attracted due to opposite charges and form the compound sodium chloride (table salt).
- In solid form, sodium chloride is a crystal; in water, it dissociates into ions.
Importance of Ions and Ionic Bonds
- Ions are involved in many physiological processes, especially in water and across cell membranes.
- Ionic bonds involve the transfer of electrons; atoms become ions with unequal numbers of protons and electrons.
- Positive ions are called cations; negative ions are called anions.
Key Terms & Definitions
- Ion — An atom with a net electrical charge due to loss or gain of electrons.
- Electronegativity — The strength an atom has to attract electrons in a bond.
- Cation — Positively charged ion (e.g., Na⁺).
- Anion — Negatively charged ion (e.g., Cl⁻).
- Ionic Bond — Attraction between cations and anions.
Action Items / Next Steps
- Review section on electron configurations and practice drawing them.
- Prepare for discussion on hydrogen bonds in the next class.