atom
atomic
atomic size
cartoon
challenge
charge
chemical
chemistry
circle
complete
diagram
education
effect
effective
effective nuclear charge
electron
electronegativity
element
energy
fun
homework
illustration
ionization
logic
many
match
metallic
model
nuclear
nucleus
number
number of shells
periodic
physics
printable
property
puzzle
quantum
radius
science
screening
shell
shells
shielding
size
structure
table
worksheet