Contains only one kind of atom. A pure substance that cannot be separated into simpler substances by physical or chemical means|Matter that is composed of two or more elements that are chemically combined|Atomic and molecular makeup is the same throughout the matter|An arrangement of the elements according to their atomic numbers and periodic trends of physical and chemical properties|A mixture of mainly nitrogen and oxygen, with small amounts of other gases that surround Earth|Anything that has mass and takes up space|Periods The rows in a periodic table that classifies the elements by select characteristics Atom The smallest unit of an element that has all of the properties of that element|The symbol which represents each element on the Periodic Table|Fist element on the periodic table. Atomic Symbol is H|A group of atoms chemically bonded together - can be same element or different elements|A combination of two or more elements or compounds which have not reacted to bond together|Atomic Number is 26, Symbol is Fe|NaCl, also called Sodium Chloride|Atomic mass is 183.84, Symbol is W|It's bananas that this element's symbol is K