Questions: A selenium ion ( Se^2- ) is in its ground state. How many electrons are in a neutral selenium atom? How many electrons are in a selenium ion ( Se^2- )? Complete the ground-state electron configuration of a selenium ion ( Se^2- ) using noble gas notation.

A selenium ion ( Se^2- ) is in its ground state.

How many electrons are in a neutral selenium atom?

How many electrons are in a selenium ion ( Se^2- )?

Complete the ground-state electron configuration of a selenium ion ( Se^2- ) using noble gas notation.

Transcript text: A selenium ion ( $\mathrm{Se}^{2-}$ ) is in its ground state. How many electrons are in a neutral selenium atom? $\square$ How many electrons are in a selenium ion ( $\mathrm{Se}^{2-}$ )? $\square$ Complete the ground-state electron configuration of a selenium ion ( $\mathrm{Se}^{2-}$ ) using noble gas notation. $\square$

Solution

Solution Steps

Step 1: Determine the Number of Electrons in a Neutral Selenium Atom

Selenium (Se) is element number 34 on the periodic table.
A neutral selenium atom has 34 electrons.

Step 2: Determine the Number of Electrons in a Selenium Ion ($\mathrm{Se}^{2-}$)

A $\mathrm{Se}^{2-}$ ion has gained 2 additional electrons compared to a neutral selenium atom.
Therefore, $\mathrm{Se}^{2-}$ has $34 + 2 = 36$ electrons.

Step 3: Write the Ground-State Electron Configuration of $\mathrm{Se}^{2-}$ Using Noble Gas Notation

The noble gas preceding selenium is argon (Ar), which has 18 electrons.
The electron configuration for a neutral selenium atom is $[ \text{Ar} ] \, 3d^{10} \, 4s^2 \, 4p^4$.
For $\mathrm{Se}^{2-}$, with 36 electrons, the configuration is $[ \text{Ar} ] \, 3d^{10} \, 4s^2 \, 4p^6$, which is equivalent to $[ \text{Kr} ]$.