Answer:
The first 20 Elements of the Periodic Table: Hydrogen, Helium, Lithium, Beryllium, Boron, Carbon, Nitrogen, Oxygen, Fluorine, Neon, Sodium, Magnesium, Aluminium, Silicon, Phosphorus, Sulphur, Chlorine, Argon, Potassium, Calcium.
Mnemonic:
Harry He Likes Beer Bottle Cold, Not Over Frothy. Nelly's Nanny Might, Although Silly Person, She Climbs Around Kinky Caves;
Mnemonic:
He Has Light Brain But Can Not Offer Full Nine Subjects, May All Senior Professional Scientists Come And Protect Chemistry
Mnemonic:
He Has Large Brain But Can Not Offer Full Nine Subjects, Master Art Students Prefer Simple Colours And Pretty Colours
Mnemonic:
"H.HeLi, B.BCNOF and NeNa MgAl SiPS ClArKCa"
Mnemonic:
"Hi Helen, Listen B.B.C. News On Friday N(e)ight. Naughty Maggie Always Sings Pop Songs. Clever Archie Kissed Cathy."