Question #fd6bc

Oct 5, 2016

Here's what's going on here.

Explanation:

In the video, Tyler says that

the oxygen and hydrogen pair can steal an electron from somewhere else

That basically means that in order to have a hydroxide anion, ${\text{OH}}^{-}$, you need to have a corresponding cation, which is a positively charged ion.

In other words, the hydroxide anion is formed when the oxygen and hydrogen pair take an electron from elsewhere, usually from a metal atom.

A classic example would be sodium hydroxide, $\text{NaOH}$, an ionic compound that contains sodium cations, ${\text{Na}}^{+}$, and hydroxide anions.

When this oxygen and hydrogen group reacts with a sodium atom, $\text{Na}$, it picks up sodium's single valence electron. This gives rise to the sodium cation and to the hydroxide anion, which are then brought together by the electrostatic force of attraction to form $\text{NaOH}$.

Another example to consider here is the auto-ionization of water, which produces hydronium cations, ${\text{H"_3"O}}^{+}$, and hydroxide anions, ${\text{OH}}^{-}$

$2 {\text{H"_ 2"O"_ ((l)) rightleftharpoons "H"_ 3"O"_ ((aq))^(+) + "OH}}_{\left(a q\right)}^{-}$

Here one water molecule picks up a proton, ${\text{H}}^{+}$, from the other, leaving behind the hydroxide anion.

Long story short, the oxygen and hydrogen group that forms the hydroxide anion picks up an electron from another atom.

Tyler didn't mention this in that particular video because he wanted to focus exclusively on polyatomic ions and how their bonding works.