Question

# What is the electron configuration of iodide ion (I$^-$)?

Solution

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To determine the electron configuration of $\ce{I^-}$ ion, first we need to determine the electron configuration of $\ce{I}$ atom.

The atomic number of $\ce{I}$ is 53.

When writing electron configuration, some rules need to be followed:

Each orbital can be occupied by 2 electrons with opposite spins.

- s subshell has 1 orbital (can hold up to 2 electrons)

- p subshell has 3 (can hold up to 6 electrons)

- d subshell has 5 (can hold up to 10 electrons)

- f subshell has 7 orbitals (can hold up to 14 electrons)

Aufbau Principle - electrons occupy the lower energy orbitals before occupying the higher energy orbitals.

Hund's Rule- electrons will singly occupy the empty orbitals in a subshell, before occupying them doubly.

Pauli-Exclusion Principle - the two electrons occupying the single orbital, must have opposite spins.