Question

What are the terms that describe these values for the element oxygen?

Answer 1

The 8 represents the Oxygen's Atomic Number. The 18 represents the Atomic Mass. The atomic mass is equivalent to the number of protons and neutrons in the element.

Answer 2

Answer: 18 = Mass umber

8 = atomic number

Explanation:

An atom is smallest unit of a matter or substance.It consist of three subatomic particles : electrons, protons, neutrons.

Protons and neutrons are located in the center of an atom where while mass of an atom is concentrated.

Mass number = Number of protons + Number of neutrons

Atomic number = Number of protons = Number of electrons (for a neutral atom)

General representation of an element is given as: $_Z^A\textrm{X}$

where,

Z represents Atomic number

A represents Mass number  

X represents the symbol of an element

Oxygen is the 8th element of the periodic table and is written as $_8^{16}\textrm{O}$, thus 8 = atomic number and 18= Mass number