Chapter 17 Section 1 Part A Composition of Matter

Pure Substances Pure substances cannot be broken down and still have the same properties Properties are characteristics we can describe or measure Two kinds of pure substances: Elements Compounds

Elements Elements make up all matter Elements are made up of atoms that are similar Atom: smallest part an element can be broken into and still have the properties of the element Atoms made up of 3 subatomic particles Protons Neutrons Electrons

Elements 90 naturally occurring elements Organized on the periodic table Elements can be broken into 3 groups: Metals Nonmetals Metalloids Each atom of the same element has the same number of protons (ALWAYS!)

Compounds Compounds are chemical combinations of two or more elements The atoms are always in the same ratio in a compound Example: water is Bonding holds the atoms of compounds together Two kinds of bond: Ionic Covalent

Compounds Compounds are formed by chemical reaction Atoms break and re-form bonds in a chemical reaction The only way we can change an element is by a nuclear reaction Two main kinds of nuclear reaction: Fusion: Fission:

Fusion vs Fission Fusion: Fission: Two atoms come together to make a larger atom Occurs in stars Fission: Atom breaks apart into smaller atom(s) Occurs in radioactive elements