Periodic system of elements

For easy calculation of molecular weights,
you may find our on-line Molecular Weight Calculator useful

Notes: the atom number is equal to the number of protons the atom mass is averaged for the major naturally occurring isotopes the atom mass is approximately equal to the number of protons and neutrons

atom number	symbol	name	atom mass [approx]	#neutrons
1	H	hydrogen	1	0
2	He	helium	4	2
3	Li	lithium	7	4
4	Be	berilium	9	5
5	B	bohrium	10.8	5 or 6
6	C	carbon	12	6
7	N	nitrogen	14	7
8	O	oxygen	16	8
9	F	fluor	19	10
10	Ne	neon	20.2	10 or 12

(to be continued...)