CHEM104 Lecture Chapter 2: Periodic Trends

Overview

Discussion on periodic trends in electron configurations, valence electrons, Lewis diagrams, and elements' physical and chemical properties.
Focus on two key properties: atomic radius and ionization energy.

Definition: Half the diameter of an atom, visualized as a small sphere.
Trends:
- Increases down a column (group) in the periodic table.
- Decreases from left to right across a row (period).
Examples:
- From hydrogen to lithium to sodium, atomic radius increases.
- From lithium to beryllium to boron, the radius decreases across a period.
- When comparing atoms like lithium and beryllium (same row), the larger atom (lithium) is on the left.
- For vertically stacked atoms like nitrogen and phosphorus, the larger atom (phosphorus) is lower.
- Diagonal comparisons: Silicon is larger than nitrogen as it is both to the left and down.

Definition: The energy required to remove an electron from an atom, creating a positive cation.
Trends:
- Tends to increase up a column and from left to right across a row.
- Opposite of the atomic radius trend.
Examples:
- Beryllium has higher ionization energy than lithium as it is further right in the row.
- Nitrogen has higher ionization energy than phosphorus because it's higher up in the column.
- For comparisons like silicon and nitrogen, nitrogen has higher ionization energy as it is higher and to the right.

Use periodic table trends to predict:
- Which atom has a larger radius.
- Which atom has a higher ionization energy.

Note: Some exceptions exist in ionization energy trends, but they are not required for this class.