Why is LiBr ionic?

[Edin_Dzeko]

Li (Electronegativity) = 1.0
Br (Electronegativity) = 2.8

2.8 - 1.0 - 1.8

Ionic = 2.0+
Polar = .4 - 2.0+
Non polar covalent = 0 - 0.4

1.8 doesn't it fall into the polar range? I got that wrong on a h.w. question

[student54321]

We round the electronegativity of lithium to 1.0, and bromide to 3.0, so the difference is actually 2.0.

It is also ionic because it is a bond between a metal and non-metal.

[Borek]

We round the electronegativity of lithium to 1.0, and bromide to 3.0, so the difference is actually 2.0.

This is way too handwavy for my liking. Selectively rounding you can prove anything, including 0=1.

It is also ionic because it is a bond between a metal and non-metal.

So why is AlCl3 covalent?