Question

Are these cations, how do i know?

BF3, BH3, AlCl3, FeCl3

how do i recognize a cation?

Answers

All of the chemicals in your problem are compounds. Only ionic compounds contain cations.

The definition of "cation" is a positively charged ion.

Here's how you can recognize a cation:

It is the metal part of an ionic compound. an ionic compounds is made up of a metal and and a nonmetal.

The metal is always written first in the formula.

Remember that metals are found on the left side of the step on the periodic table.

BF3: The first element, B, is not a metal. So this is NOT an ionic compound and there is no cation here.

BH3: Same thing as BF3

AlCl3: the first element, Al, is a metal. This is an ionic compound and Al is the cation (Al's charge here is +3).

By the way, Cl is the nonmetal negative ion here. It's called an "anion". (Each Cl has a charge of -1 here)

FeCl3: the first element, Fe, is a metal. This is an ionic compound and Fe is the cation (Fe's charge here is +3).

#1

the left side is a cation

F- ; H- ; Cl- ; Cl -

#2