Someone help me, How do i find which atom is which just by the valance electrons and protons and neutrons? I know it has something to do with periods and groups.

You can get the valence electrons in an atom's electronic arrangement by consulting the periodic table:

Explanation:

The Group 1 atoms have 1 valence electron.

The Group 2 atoms have 2 valence electrons.

The Group 3 atoms have 3 valence electrons.

The Group 4 atoms have 4 valence electrons.

Alrighty so I’m a little unsure of what you’re asking, but I’ll try my best!
Every atom has a specific number of Protons that only that atoms contains.
Neutrons can variety by the atom which gives you an Isotope.
The Protons and an unboned Atom’s Electrons are the same.
To find the Valence from just the proton number you can use this equation :

protons = electrons

# of electrons - 2 = the first layer
# of leftover electrons - 8 = the second layer and just keep going until one layer is not full

Mg (s) + 2HCl > H2(g) + MgCl2 (aq)

Explanation:

This reaction produces hydrogen gas and magnesium chloride. So, we have :

Mg (s) + HCl > H2 (g) + MgCl2 (aq)

In other to balance this reaction, we then add "2" to HCl on the left hand side of the equation so that the number of hydrogen and chlorine on both sides will be equal.

Thus our balanced equation would be:

Mg (s) + 2HCl (aq) > H2 (g) + MgCl2 (aq)