Atoms

Its in the middle of the atom. it contains protons and neutrons. (its the number of protons in an atom that decides what element it is)

the nucleus has an overall positive charge because protons are positively charged while neutrons have no charge

almost the whole mass of the atom is concentrated in the nucleus. but sized-wise its tiny compared to the atom as a whole

They move around the nucleus in energy levels called shells (each shell is only allowed a certain number of electrons)

They have a negative charge ( electrons and protons have equal but oposite charges)

They're tiny compared to the nucleus ( they have virtually no m***), but as the move around they cover a lot of space.( the size of thir orbits determines how big the atom is)

neutral atoms have no charge overall

this is because the number of protons always equal the number of electrons in a neutral atom,and the charge on the electrons is the same size as the charge on the protons but opposite

the number of neutrons isn't fixed but is usually about the same as the number of protons 

Protons are heavy and positvely charged

Neutrons are heavy and neutral (no charge)

Electrons are tiny and negatively charged

the atomic number says how many protons there are in an atom, and is unique to that element

the atomic number also tells you the number of electrons

the mass number is the total number of protons and neutrons in the atom. so if you want to find the number of neutrons in an atom, just subtract the atomic numbers from a mass number