Question

What is the electron configuration of salt?

Answer 1

Assuming you mean `NaCl` (and not simply sodium), it is not as simple as something like `1s^2 2s^2 cdotcdotcdot`.

The electron configuration of `Na` is:

`1s^2 2s^2 2p^6 3s^1`
`= [Ne] 3s^1`

That for `Cl` is:

`1s^2 2s^2 2p^6 3s^2 3p^5`
`= [Ne] 3s^2 3p^5`

If you mean them to be bonded, read on... The resultant VALENCE electron configuration is:

`(sigma_(3s, "nb"))^2 (sigma_(3p_z))^2 (pi_(3p_x))^2 (pi_(3p_y))^2`

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DISCLAIMER: LONG ANSWER!

This is the MO diagram for NaCl (couldn't find a better one):

Writing the configuration for them when bonded would require you to know what molecular orbitals (MOs) are made from what atomic orbitals (AOs) when these two atoms bond.

To figure this out, you would have to construct or have an accurate MO diagram. Let `"*"` denote antibonding and no `"*"` indicate bonding.

• Two `ns` orbitals combine to form one `sigma_(ns)` and one `sigma_(ns)^"*"` bonding and antibonding molecular orbitals, respectively.

• Two `np_(x)` and `np_(y)` orbitals combine to form a `pi_(np_x)` and `pi_(np_y)`, and one `pi_(np_x)^"*"` and `pi_(np_y)^"*"` bonding and antibonding molecular orbitals, respectively.

• Two `np_z` orbitals combine to form one `sigma_(np_z)` and one `sigma_(np_z)^"*"` bonding and antibonding molecular orbitals, respectively.

Given the above MO diagram, the configuration will contain the total number of electrons given by `"Na"` and `"Cl"` (`11 + 17 = 28`). Keep in mind that the above MO diagram omits the following orbitals that are low in energy:

• `sigma_(1s)`, `sigma_(1s)^"*"`
• `sigma_(2s)`, `sigma_(2s)^"*"`
• `pi_(2p_x)`, `pi_(2p_x)^"*"`
• `pi_(2p_y)`, `pi_(2p_y)^"*"`
• `sigma_(2p_z)`, `sigma_(2p_z)^"*"`

which would have contained `10 xx 2 = 20` of the `28` total electrons.

So, the particular MO diagram depicted above would fill up with only `bb8` valence electrons.

The valence electron configuration would then be:

Valence electron configuration -----

`color(blue)((sigma_(3s, "nb"))^2 (sigma_(3p_z))^2 (pi_(3p_x))^2 (pi_(3p_y))^2)`

Note that the `sigma_(3s)` orbital is nonbonding because the ionic character of `"NaCl"` is large, and thus the `3s` orbital energies differ a lot, disallowing their interaction.

Furthermore, the molecular orbital depictions have the `"Cl"` orbitals much larger, so it means that `"Cl"` owns most of the electron density, which makes sense because this is an ionic compound.