what conclusions can you make about the elements sodium, potassium, and francium?; what atoms combine to make up a molecule of water, h2o?; a majority of the 118 elements on the periodic table are classified as; what is the main principle behind the law of conservation of matter?; elements in the second group are extremely reactive they are called; elements in the first group are extremely reactive. they are called; the energy necessary to remove an outer shell electron from an atom.; what is group 2 on the periodic table called