the atom/periodic table

• atom: the smallest particle of an element that still has the properties of that element
• element: a substance that cannot be broken down into simpler substances by chemical means
• compound: a substance that is made up of 2 or more different elements combined together chemically
• molecule: formed when 2 or more atoms join together chemically
• mixture: 2 or more different substances mingled together but not chemically combined
• atomic number: number of protons in nucleus of an atom (always smaller number)
• mass number: the number of protons and neutrons in nucleus of an atom
• groups go down and periods go across
• group 1: alkali metals (group 1 because they have 1 electron in outer shell, very reactive)
• group 2: alkaline earth metals
• bottom groups of table: transition metals
• second last row: halogen: 7 electrons in outer shell
• last group: noble gases: full outer shell