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Elements • It has to be on the Periodic Table. • Elements are “pure” meaning they cannot be broken down chemically. Periodic Table • period • group • Group 1: alkalis • Group 17: halogens • Group 18: Noble Gases Atomic Math • Atomic number = the number of protons • Atomic mass = # of protons + # of neutrons o So # neutrons =? Element vs. Compound • Elements • Compounds • found in nature • is on the Periodic Table of the Elements • contains only 1 element • some needed for life • smallest part of an element is an atom • found in nature • Examples: carbon, oxygen, iron • has 2 or more elements • some needed for life • smallest part of a compound is a molecule • created by a chemical reaction • Examples: water, carbon dioxide Examples of Chemical Properties • • • • • • flammability (it can burn) reactivity to oxygen (corrosion) reactivity to light reactivity to water reactivity to electricity reactivity to acid Signs of a Chemical Change • • • • • • • • releasing a gas, bubbling a change in temperature forming a precipitate (a solid) a change in color reacting with oxygen (burning or rusting) giving off light making a noise (explosion) not reversible Law of Conservation of Mass • Says the total mass before the reaction is the same as the total mass afterwards. • No matter is created or destroyed in a chemical reaction! Drawing an Atom! • The atomic number = # of protons = # of electrons • The atomic mass = total # of protons and neutrons in nucleus. • Step 1: Find the atomic mass for your element. Draw that many circles for your nucleus. Pack them close together! • Step 2: Find the atomic # for your element. Color that many circles for your protons. Spread them around the entire nucleus. • Step 3: Color the rest of your nucleus as neutrons. • Step 4: Draw the electrons around the nucleus, completely surrounding it. The number is the same as the number of protons.