Electron Configuration and Periodic Properties

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Electron Configuration

Electron Configuration

The number of electrons in an atom's highest occupied every level determines its properties.

Elements with similar chemical properties are in the same group and almost always have the same number of electrons in their outermost energy shell.

The outermost occupied energy level also determines which period of the period table an element resides in.

If an element's outermost occupied energy level is 5, they will be located in the 5th period.

1s2 2s2 3s2: 3 is the highest energy level, therefore it is in period #3. Blocks of the Periodic Table

The periodic table is also divided into blocks: the s, p, d and f blocks.

Each block is occupied by elements that are filling or have completely filled the block's sub level.

Blocks = farthest to the right on the periodic table.

Example: [Kr]5s2 - configuration for Sr places this element into the s-block.

Example: [Ar]3d24s2 - configuration for Ti places this element into the d-block, because the d-block is farthest to the right on the periodic table.

s -- f -- p -- d

d-block elements

Looking for Group Number? Add exponents!

All elements in the d-block are metals, but are less reactive than Groups 1 and 2.

There is at least 1 electron in a d orbital.

You can determine what Group a d-block element in in from its electron configurations by adding the superscripts of the d and s orbitals.

Example: [Ar] 3d104s1: 10 + 1= 11: this element is in Group 11.

18 Groups total.

NEVER add f.

If ONLY s and p, then you must add 10!

p-block elements

Groups 3-18 except He

If you subtract 10 from the group number of an element, you know exactly how many electrons are in its outermost energy shell.

Example: Cl is in Group 17 so 17-10=7. Therefore Cl has 7 electrons in its outermost energy shell.

Valence Electrons = highest energy level of electrons.

Group number = the number of valance electrons (1-12). For Groups 13-18, subtract 10.