Mnemonic Device:
 Happy Henry Lives Beside Boron Cottage, Near Our Friend Nelly Nancy MgAllen. Silly Patrick Stays Close. Arthur Kisses Carrie.
 Here He Lies Beneath Bed Clothes, Nothing On, Feeling Nervous, Naughty Margret Always Sighs, â€ť Please Stop Clowning Around â€ť (18 elements)
 How He Likes Bear By Cups Not Overflowing. Although Science Presents Some Clues, Are Kittens Cats?
Explanation:
Happy. â€“ H Hydrogen
Henry â€“ He Helium
Lives â€“ Li Lithium
Beside â€“ Be Beryllium
Born â€“ B Boron
Cottage â€“ C Carbon
Near â€“ N Nitrogen
Our â€“ O Oxygen
Friend â€“ F Fluorine.
Nelly â€“ Ne Neon
Nancy â€“ Na Sodium
Mg â€“ Mg Magnesium
Allen â€“ Al Aluminum
Silly â€“ Si Silicon
Patrick â€“ P Phosphorus
Stays â€“ S Sulphur
Close â€“ Cl Chlorine
Arthur â€“ Ar Argon
Kisses â€“ K Potassium
Carrie â€“ Ca Calcium
Additional Information:Â the first twenty elements, of the periodic table, with their atomic number
1. hydrogen H
2. helium He
3. lithium Li
4. beryllium Be
5. boron B
6. carbon C
7. nitrogen N
8. oxygen O
9. flourine F
10. neon Ne
11. sodium Na
12. magnesium Mg
13. aluminum Al
14. silicon Si
15. phosphorus P
16. sulfur S
17. chlorine Cl
18. argon Ar
19. potassium K
20. calcium Ca
Find the average atomic mass:
Rules to find the average atomic mass, if the atomic number (Z) is an:
Even number except Be (9), Ar (40),

multiply the atomic number by 2. For example,
 1) Helium atomic number (Z) is the EVEN #2, hence to find the average atomic mass (A) is (Atomic number) multiply by 2 which is 2 x 2 = 4
Odd number except H (1), N (14 ), Cl (35.5),

multiply the atomic number by 2, then add 1. For example,
 1) Lithium atomic number (Z) is the ODD # 3, hence to find the average atomic mass (A ) is (Atomic number) multiply by 2 plus 1, which is 3 x 2 +1 = 7
 2) Boron atomic number (Z) is the ODD # 5, hence to find the average atomic mass (A ) is (Atomic number ) multiply by 2 plus 1, which is 5 x 2 +1 = 11
Please remember the exception to the rules:
 Be, Ar, H, N, Cl
Song for the first 20 elements:
Many more mnemonics for remembering the elements of the periodic table
See https://en.wikipedia.org/wiki/Periodic_tableÂ for more information.
Each n every1 must learn
That really, really helped me be able to get an 100% on my science test on the first 20 elementsin the perodic table. My teacher commented to me and said, â€śdid you cheatâ€ť:)
Thanx a lot very much ?? u made it easier bro ??