how to determine how many atoms of each element are present?

Question

heres a few problems
1)CaF2
2)Fe(OH)2
3)NO2
4) Al2(SO4)3
5)NH4NO3
6)SF2

Answer 1

The number to the bottom right tells you how many atoms of a certain element are present: (example O2 would be 2 atoms of oxygen). If there is no number then you assume that it is a one: (example H would be 1 atom of hydrogen). If a number is to the bottom right of a parentheses then it applies to all elements in the parentheses: (example (CO)2 would be 2 carbon atoms and 2 oxygen atoms ). If an element in the parentheses already has a number next to it then you multiply the number next to the element times the number outside of the parentheses. Example (H2O)6 would be 12 hydrogen atoms and 6 oxygen atoms.
Problems:
1) 1 atom calcium 2 atoms Florine
2) 1 atom iron 2 atoms oxygen 2 atoms hydrogen
3) 1 atom nitrogen 2 atoms oxygen
4) 2 atoms aluminum 3 atoms sulfur 12 atoms oxygen
5) 2 atoms nitrogen 4 atoms hydrogen 3 atoms oxygen
6)1 atom sulfur 2 atoms fluorine

Answer 2

1. Count each individual atom: atom symbols can be one or two letters, they always start with a capital letter.

2. If there is a subscript, that is how many atoms of that type there are (i.e. CaF2 = 1 Ca, 2 F = 3 atoms total)

3. If the formula includes brackets with a number outside, there are that many of the bracketed group.
(ie. Al2(SO4)3 = 2 Al + 3 SO4 groups.
= 2 Al + SO4 + SO4 + SO4
or
= 2 Al + 3 S + 3*4 O
= 2 Al + 3 S + 12 O

Answer 3

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Mg = 1 atom O = 2 atoms H = 2 atoms relative mass = 24 + 2(16 + 1) = 58 g/mol

Answer 4

The formula shows you that

For example, CaF2 has one calcium atom and 2 fluorine atoms