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The Periodic Table of Elements What is an element? An element is a pure chemical made of only one type of atom Each box on the periodic table represents one element Reading the Periodic Table (Z) (A) Atomic number (Z) Each element has its own unique atomic number It is based on the number of protons present in the atom Always Ex: a whole number 7, 22, 91, etc In a true atom, the number of protons is equal to the number of electrons. Element Symbol Each element is given a 1 or 2 letter abbreviation. The first letter has to be capitalized. If there is a second letter, it is always lowercase. Atomic Mass (A) This tells you how heavy an individual atom is. Since atoms are so small, we must use a special unit. It is called the atomic mass unit (amu). Calculating the Atomic Mass Each proton weighs ~1amu Each neutron weighs ~1amu Electrons the mass are so small they do not affect Atomic mass = # of protons + # of neutrons Why isn’t the atomic mass a whole number? The atomic mass shown on the periodic table is actually an average of the various isotopes that exist. When making calculations, we round to the nearest whole number. Calculating Average Atomic Mass (mass of isotope1 x % in nature)+ (mass of isotope2 x % in nature) 100 * You may have more than two isotopes Example: Mass of carbon (12 x 98.9%) + (13 x 1.1%) + (14 x 0.0001%) 100% =12.01amu