1. Isotopes differ in the number of neutrons they have in their nucleus.   True   False   2. Isotopes have similar chemical properties.   True   False   3. The atom is mainly empty.   True   False   4. Electrons are present in the nucleus.   True   False   5. The elements are arranged in order of decreasing atomic numbers in a table called the periodic table.   True   False   6. The smallest atom is that of hydrogen.   True   False   7. The number of electrons in a neutral atom is equal to its atomic number.   True   False