Nucleus

An atom has a tiny nucleus at its centre. The nucleus contains positively charged protons and uncharged neutrons, so it is positively charged overall. Negatively charged electrons are found around it.

An atom has a tiny central nucleus surrounded by negatively charged electrons. The nucleus contains two kinds of particle: positively charged protons and uncharged neutrons.

Because an atom has no overall electric charge, Thomson proposed that its negative electrons were embedded in a sphere of positive charge, balancing them. This became known as the plum pudding model. It had no central nucleus: the positive charge was spread throughout the atom.

An atom has a tiny nucleus at its centre. The nucleus contains positively charged protons and uncharged neutrons, so it has an overall positive charge. Negatively charged electrons surround it at different energy levels, often called shells.