How do you determine the atomic number of an atom?

Answer 1

Follow these 5 Rules1) The oxidation number of the atoms in a neutral molecule must add up to zero, and those in a charged ion must add up to the charge on the ion.

2) Alkali metal atoms (first column in the Periodic Table) have oxidation number +1, alkaline earth atoms (2nd column) have oxidation number +2.

3) Fluorine always has oxidation number -1. Other halogens (next-to-last column in the periodic table) usually have oxidation number -1, except when they are bonded to oxygen or other halogens, when they can have positive oxidation numbers.

4) Hydrogen has oxidation number +1 except in metal hydrides, such as LiH or CaH2, where Rule #2 takes precedence, and hydrogen has oxidation number -1.

5) Oxygen has oxidation number -2, with two exceptions: In compounds where it is bonded to fluorine, Rule #3 takes precedence, and in compounds with O-O bonds, Rules #2 and #4 take precedence. So, for example, the oxidation number in OF2 is +2, and the oxidation number in peroxides such as H2O2 is -1 (and superoxides, the oxidation number is -1/2)

It is also convenient to know the charge on these common ions:

Nitrate is minus one: NO3-

Hydroxide is minus one: OH-

Sulfate is minus two: SO42-

Carbonate is minus two: CO32-

Phosphate is minus three: PO43-

Ammonium is plus one: NH4+

Answer 2

The atomic number of an atom is equal to the number of protons in its nucleus. It is a unique property for each element on the periodic table. You can find the atomic number above the atomic symbol of an element on the periodic table.

Answer 3

To determine the atomic number of an atom, one must determine the number of protons. The atomic number is always the same with the number of protons.