1 Complete the passage using the words provided. Words may be used once, more than once or not at all. electrons isotopes neutrons nucleon nucleus proton protons shells Atoms are made up of three different particles: which are positively charged which have no charge which are negatively charged. The negatively charged particles are arranged in different atom. The particles with a negligible mass are the and ....... (energy levels) around the of the All atoms of the same element contain the same number of are known as Atoms of the same element with different numbers of 2 An atom of lithium has three protons and a nucleon number of 7. a How many electrons are in the lithium atom? b How many neutrons does lithium have? ..... с What is the mass number of this lithium atom? d Describe the lithium atom in the format that uses two numbers and the symbol for the element.​