Overview
This lecture covers the properties, trends, and reactions of Group 1 elements (alkali metals), focusing on their reactivity, electron structure, and typical compounds formed.
Properties of Alkali Metals
- Group 1 elements include lithium, sodium, potassium, rubidium, caesium, and francium.
- Alkali metals are soft, have low densities, and low melting points compared to most metals.
- They are highly reactive, especially with water, oxygen, and Group 7 elements like chlorine.
- Melting and boiling points decrease as you move down the group.
- Reactivity increases down the group, with caesium being the most reactive.
Reactivity and Trends
- All alkali metals have one electron in their outermost shell.
- They easily lose this single electron to gain a full outer shell and become stable.
- Losing the outer electron forms a +1 ion (cation).
- Atomic radius increases down the group, so the outer electron is further from the nucleus and removed more easily.
- Increased distance from the nucleus leads to increased reactivity down the group.
- Alkali metals form ionic compounds by transferring their electron to nonmetals.
Ionic Compounds of Alkali Metals
- Ionic compounds form when alkali metals lose an electron and nonmetals gain it, resulting in oppositely charged ions.
- These compounds are white solids that often dissolve in water to give colorless solutions.
- Example: Sodium (Na) and chlorine (Cl) form sodium chloride (NaCl), which is table salt.
Reactions with Water, Chlorine, and Oxygen
- Alkali metals react vigorously with water to produce a metal hydroxide and hydrogen gas.
- Example: Sodium + water → sodium hydroxide + hydrogen.
- Reactions with water become more energetic down the group, sometimes igniting hydrogen gas.
- With chlorine gas, alkali metals form white metal chlorides (e.g., sodium + chlorine → sodium chloride).
- With oxygen, they form different metal oxides and peroxides (e.g., lithium forms Li₂O; sodium forms Na₂O or Na₂O₂; potassium forms K₂O₂).
Key Terms & Definitions
- Alkali Metals — Group 1 elements on the periodic table, very reactive metals.
- Reactivity — How easily an atom loses or gains electrons to react with other atoms.
- Ionic Compound — Compound formed by the transfer of electrons from a metal to a nonmetal, resulting in oppositely charged ions.
- Atomic Radius — The distance from the nucleus to the outermost electron shell in an atom.
- Cation — A positively charged ion, formed when an atom loses electrons.
Action Items / Next Steps
- Use flashcards to memorize which oxides and peroxides are formed by each alkali metal.
- Review reactions of alkali metals with water, chlorine, and oxygen for exams.