Overview
This lecture covers periodic trends in the periodic table, focusing on atomic radius, electronegativity, ionic radius, and how these trends relate to element properties and positions in the table.
Atomic Radius Trends
- Atomic radius increases going down a group (column) due to added energy levels farther from the nucleus.
- Atomic radius decreases across a period (row) as increased nuclear charge pulls electrons closer.
- Al, S, Br, Na, O, and Ca have the largest atomic radii in their pairs (Al vs B, S vs O, etc.).
- Order of atomic radius from smallest to largest: O < C < Sn < Sr.
Electronegativity Trends and Ionic Radius
- Electronegativity is the ability of an atom to attract electrons in a covalent bond.
- Ionic radius of a nonmetal ion is larger than its atomic radius due to electron-electron repulsion when gaining electrons.
- Electronegativity decreases down a group because valence electrons are farther from the nucleus.
- Electronegativity increases across a period as nuclear charge increases.
- O, Cl, Br, Sr, and O have the higher electronegativity in their respective pairs.
Ion Formation and Group Properties
- Alkali metals (group 1) tend to form +1 ions.
- Alkaline earth metals (group 2) tend to form +2 ions.
- Halogens (group 17) tend to form -1 ions.
- Noble gases (group 18) do not typically form ions or react.
Application: Comparing Elements
- In the set Li, Be, Mg, Na: Na has the lowest electronegativity and largest atom, Be has the least metallic character.
- In P, S, Cl, F: F has the highest electronegativity and least metallic character, P has the largest ion.
- In Au, Zn, S, Si: S has the highest electronegativity, Au has the most metallic character and is the largest atom.
Periodic Table Classification and Trends
- Metals lose electrons in bonding and conduct electricity.
- Halogens are group 17, noble gases are group 18, alkaline earth metals are group 2, alkali metals are group 1.
- Increasing electronegativity and nonmetallic character go up and right; increasing atomic radius and metallic character go down and left.
Key Terms & Definitions
- Atomic Radius — Distance from the nucleus to the outermost electron shell.
- Electronegativity — The ability of an atom to attract electrons in a covalent bond.
- Ionic Radius — The size of an atom's ion, larger in nonmetals when they gain electrons.
- Valence Electrons — Electrons in the outermost shell involved in bonding.
- Metallic Character — How readily an atom loses electrons, increasing down a group.
Action Items / Next Steps
- Complete the chart on atomic number, group, period, valence electrons, and classification for K, Mg, Ne, N, Cl, and Si.
- Review periodic table group numbers and family characteristics.
- Practice identifying trends and comparing properties among element sets.