There are 2 hydrogen atoms, one magnesium atom, and 5 atoms in total.
Explanation:
We are given a compound in formula form. To make things easier to understand, we can first convert this to the name of the compound.
When a compound contains one or more elements in parentheses, these are usually a <u>polyatomic ion</u>.
Polyatomic ions are ions made up of two or more elements with a positive or negative charge over the entire ion. Commons examples of these NH₄⁺ (ammonia) and HCO₃⁻ (bicarbonate).
You can combine metals with polyatomic ions to create commonly known compounds, such as baking soda. The chemical name for baking soda is sodium bicarbonate, so we can combine Na (sodium) with HCO₃⁻ (bicarbonate) and create sodium bicarbonate: NaHCO₃.
This compound is one magnesium atom bonded to two hydroxide ions.
Hydroxide is the compound between one hydrogen atom and one oxygen atom. The compound overall adopts a negative charge of 1.
If we have one hydrogen atom and one oxygen atom, the most electronegative atom is written first in chemical formulas. Therefore, the symbol for Oxygen (O) goes first.
Then, write in the hydrogen atom directly after the O symbol: OH.
Finally, since we have a negative charge on the ion, we need to play a negative sign as a superscript for the compound. Therefore, this becomes OH⁻.
Now, we need to determine the charge on the Magnesium atom which is determined from the amount of valence electrons the atom has.
On a periodic table, the symbol for Magnesium is Mg and this element has 2 valence electrons.
In order to fulfill the Octet Rule, the It is more likely to give up 2 electrons to a nonmetal than it is to gain 6, so we can safely assume that the charge is ²⁺.
We need to use the criss-cross technique to transfer the charges between the element and the ion, so the negative 1 charge goes to the Mg, which does not appear (negative 1 or positive 1 are implied) and since the magnesium has a charge of positive 2, this is the subscript for the hydroxide ion.
Therefore, our compound becomes Mg(OH)₂, and we have labeled this as magnesium hydroxide.
Now, to the number of atoms:
The new charge on Mg is 1-, so there is only one atom of Mg.
The charge is 2+ on the OH ion, so there are two atoms of H and two atoms of O.
Two atoms of oxygen, two atoms of hydrogen, and one atom of magnesium add up to be five atoms in total.
