Elements

Spell it

100

It's number is 78 and it is shiny

Platinum

200

its number is 84 found in a cereal box ring

Polonium

300

It's letter is W and number is 74

Tungsten

400

Mg 12

Magnesium

500

Sc 21

Scandium

Atomic weight

100

Mercury

200 

200

Gold

196

300

Holmium

164

400

Sliver (Ag 47)

107

500

Phosphorus (P 15)

30

Element number

100

Plutonium

94

200

Tantalum (Ta)

73

300

Boron (B)

5

400

Promethium (Pm)

61

500

Barium (Ba)

56

difficult elements

100

Highly radioactive Np 93

Neptunium

200

Dy 66 used to coat disk drives

Dysprosium

300

Er 68 used to dope fiber optic cables and amplify the signal

Erbium

400

Ir 77 Hard to melt, used for spark plugs

Iridium

500

Os 76 makes other metals stronger

Osmium

Elements we use

100

used for pipes and once for paint

Lead (Pb 82)

200

Used between double windows for insulation

Argon (Ar) (bonus point if you know the number)

300

Fire starters and lightweight race car components

Magnesium (Mg 12)

400

used as a convenient portable neutron source for detection of precious metals and in oil well logging. 

Californium

500

used for cel phones, lap tops and skull plates

Tantalum (Ta 73)