Chemical Compunds and Physical vs Chemical Changes

Element – any PURE substance, made of ONLY one kind of atom, anything found on the Periodic Table is, elements are represented by ONE capital letter, sometimes may be ONE capital and ONE lower  case letter

Molecule – Two or more elements (can be the SAME or different) ex. O2 and H2O are BOTH molecules

Compound – TWO or more DIFFERENT elements combined: just look for 2 DIFFERENT capital letters put together. ex. H2O = Compound  à  O2 or H2 = NOT a Compound

ALL compounds are molecules, but NOT ALL molecules are compounds

Capital Letters – EVERY capital letter represents a single element: DIFFERENT capital letters = DIFFERENT elements

Lower Case Letters – belong to the capital letter in front of it

Subscript – the small # that is sometimes seen behind the symbol, subscript is NEVER zero, if there is no # that follows a symbol then assume there is a 1, the small # tells you how many there are of the element in front of it

Coefficient – the “Big” # in front of an element or compound, if no # in front assume that it is 1, MULTIPLY the # in front by all the small #’s that follow UNTIL you see a “+” sign

 Physical Properties – 3 Things ALWAYS Make it a Physical Property: 1. If it is a MEASUREMENT ex. Weight, height, density, mass, volume, specific heat, boiling/freezing/melting points. 2. If it explains WHAT IT IS ex. Magnetic, round(shape), size (big, small), color. 3. If it explains WHAT IT DOES ex. Good conductor, it bends, it shines.

Physical Changes - Changes in a substance that do not involve a change in the identity or chemical makeup of that substance. All Changes in state of matter are physical changes. All physical changes are not necessarily accompanied by a chemical change.

Chemical Changes - A change in a substance that involves a change in the identity or chemical makeup of that substance. All chemical changes are accompanied by a physical change.

6 Things ALWAYS Make it a Chemical

Change/Reaction:

Black → Burns

Toilet  → Temperature Change

Paper → Precipitate forms (New substance)

Cleans → Color Change (sometimes)

Good → Gas (Bubbles or Odor)