# How can functional groups be bounded?

When I read about the different kinds of functional groups, they usually have formulas like $\ce{-NH2}$, $\ce{-COOH}$, $\ce {-OH}$, etc.

What does the bar represent? Any bond? Or can it only be a covalent one?

• Yes, the bar represents any bond, which in this case can only be a covalent one. – Ivan Neretin Oct 20 '17 at 15:16
• @IvanNeretin Why? What about compunds like $\ce {NaOH}$? – Qwedfsf Oct 20 '17 at 15:18
• @Qwedfsf because OH is not a "functional" group of "Na". – ParaH2 Oct 20 '17 at 15:19
• @Qwedfsf You will not see anyone write $\ce{Na-OH}$. – Zhe Oct 20 '17 at 15:20
• I can't think of any -OH group that wouldn't be a hydroxyl group. A chemist would never consider a -COOH group to be a combination of a -C=O (a ketone) and a -OH group. // I'd also stipulate that "functional groups" are abstractions for organic chemistry. Hence the bar in organic chemistry is used for covalent bonds. – MaxW Oct 20 '17 at 15:52

Functional groups are a unifying idea in organic chemistry. There are tens of millions of different organic chemicals but many of their key properties are determined by the functional groups they contain. For example, amines (compounds with the $\ce{-NH2}$ group) are basic and often smelly; carboxylic acids (containing the $\ce{-COOH}$ group) are acidic.
The bar in the symbol represents the bond to the rest of the molecule. Sometimes chemists write this slightly differently by including a specific symbol for the rest of the molecule like this: R-OH where R is the rest of the alcohol. So a chemist might talk about a series of similar alcohols by defining R as $\ce{CH3}$ (methanol) $\ce{CH3CH2}$ (ethanol) or $\ce{(CH3)2CH}$ (isopropanol).