Question

calculate the mass number of the following first 18 elements
H
He
Li
Be
B
C
N
O
F
Ne
Na
Mg
Al
Si
P
S
Cl
Ar​

Answer 1

Answer:

For your grade you need to remember atomic masses of first 20 elements. The atomic mass is double the atomic number of an element. But it is not applicable for all the elements in the periodic table. The atomic masses of elements like He, Li, C, N, O, Ne, Si, S, Cl, Ca are double the atomic number.

Explanation:

How do u find the mass number of an element?

Together, the number of protons and the number of neutrons determine an element's mass number: mass number = protons + neutrons. If you want to calculate how many neutrons an atom has, you can simply subtract the number of protons, or atomic number, from the mass number.