The periodic table lists all the elements, with information about their atomic weights, chemical symbols, and atomic number. The arrangement of the periodic table leads us to visualise certain trends among atoms.
When dealing with compounds and their names, it helps to know the prefixes of some of the common compounds. For instance,
Mono- = 1
Di- = 2
Tri- = 3
Tetra- = 4
Penta- = 5
Hexa- = 6
And the list goes on.
However we are dealing with Arsenic
Hexabromide:
That means we have 1 Arsenic with 6 Bromides: