How do you find the atomic mass/mass number of an atom

You can find the mass number and the atomic number in the periodic table.

E.g. >>> Look at the periodic table, and find the oxygen (O):

the mass number: 15,9994u

the atomic number: 8

And find the magnesium (Mg):

the mass number: 24,3050u

the atomic number: 12

Explanation:

the number of valence electrons for each molecule or ion is shown beneath the structure. remember hydrogen will not have more than two electrons. this hydrogen is part of a covalent bond (sharing two electrons). a double bond here would cause hydrogen to share four electrons with phosphorus.

a rain shadow is a dry region of land on the side that is protected against the prevailing winds of a mountain range. the prevailing winds are the winds that occur most of the time in a particular place of the earth

prevailing winds carry air toward the mountain range. as the air rises up over a mountain range, the air cools, water vapor condenses, and clouds form. on this side of the mountains, called the windward side, precipitation falls in the form of  rain  or snow. this dry air produces a  rain shadow.