Chem230 Wiki

What is the Diagonal Effect?

- Elements have the tendency to not have characteristics of their own family, but characteristics close to the element that is right one and down one, hence the word diagonal

- Li and Mg

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- Be and Al

- B and Si


- Overall periodic trends cancel each other out

- Down the column

- size increases

- more ionic

- more basic

- less electronegative

- Across the row

- size decreases

- more covalent

- less basic

- more electronegative

- Uniqueness Principle


1) Group relationship (Be to Mg) are dominant over diagonal relationships.

2) B3+, C4+, and Si4+ do not exist as these ionic ideals due to significant covalency.