[Jules18]

We're reviewing ionic compounds, and one of the examples of an ionic compound with a polyatomic ion is NH₄Br (ammonium bromide). 
I'm wondering why the NH₄ came first, because both N and H are on the nonmetal side of the periodic table.

... Okay, well, I've seen H on both sides, but it's definitely a halogen and not an alkali metal, right?

[Fridushka]

it is placed in the 1st column because of is atomic number, but actually it belongs to halogens

[Tin Man]

It has to do with NH₄⁺, ammonium ion, being a cation on it's own. The cation is usually written before the anion in ionic compound names.

The NH₄⁺ portion itself is actually a covalently bonded molecule that has a positive charge. That positively charged molecule bonds ionically with bromide ion, Br^-. The two ions themselves are attracted to each other by differing electronegative charges, but the ammonium itself is held together by non-ionic charges.

Hopefully that isn't too confusing. If you're teacher isn't going into it, don't think too hard about it right now. Just concentrate on the fact that NH₄⁺ is its own, positively-charged unit.

[Borek]

it is placed in the 1st column because of is atomic number, but actually it belongs to halogens

No.

Hydrogen is a special case of its own. Nitpickers will discuss to death where it should be placed in periodic table - and it won't move our chemical knowledge even a tiny step ahead. Let's keep hydrogen where it was from the very begining (that is above Li) and let's avoid fruitless discussions.

[renge ishyo]

I liked where Linus Pauling put hydrogen (right above carbon) personally. It made a lot more sense in terms of its chemical behavior and properties (its electronegativity being very close to that of carbon, its elemental form is a diatomic gas, can have a +1 or a -1 charge in compounds, etc.). But then again, the table looks rather ugly when you do it this way, so I can see why they put hydrogen where they did in the end

[Tin Man]

In the end, this is a high school forum, with a probable high school student doing high school chemistry work from a high school teacher.

I'm willing to bet that he's not involved in the debate as to where to put hydrogen on the periodic table.

Let's just stick with "hydrogen's weird, but in this case (and every case you're likely to deal with in high school and undergraduate chemistry), it doesn't matter. Focus on the ammonium ion being a cohesive unit in itself, and you're set to go."

Problem solved.

[Fridushka]

it is placed in the 1st column because of is atomic number, but actually it belongs to halogens

No.

Hydrogen is a special case of its own. Nitpickers will discuss to death where it should be placed in periodic table - and it won't move our chemical knowledge even a tiny step ahead. Let's keep hydrogen where it was from the very begining (that is above Li) and let's avoid fruitless discussions.

Ooupps it was my student who post it..so sorry for it..