1. Chemistry Unit Notes
7th Grade Science

2. Basic Vocabulary Matter: Anything that has mass and volume
Mass: Amount of matter in an object
Weight: Measure of the force of attraction between objects due to mass and gravity
Volume: Amount of space an object takes up
Density: Measurement of how much mass is contained in a given volume

3. More Vocabulary
Atoms: Smallest particle of an element that has all the properties of matter:
Protons- particles in the nucleus with positive charge
Electrons- particles orbiting around nucleus with negative charge
Neutrons- particles in the nucleus with no charge
Elements: Simplest form of a pure substance
Compounds: Two or more elements chemically combined to form a new substance

4. Sub-Atomic Particles Part of Atom Charge Location Mass/Size Electron
- negative
outside nucleus
.0006 amu
(too little to count)
Proton
+ positive
inside nucleus
1 amu
Neutron
no charge

5. Periodic Table

6. Using the Periodic Table
Atomic Number
Equal to # protons = # electrons
Periodic Table is arranged by this number
Symbol
“Shorthand” for the element – Note 2nd letter is always lowercase
Atomic Mass Number
Total AVERAGE mass of Protons + Neutrons + Electrons 17 Cl
35.5

7. More Practice
Determine the name, number of protons, neutrons and electrons for each element shown and draw… 6 8 1 C O H 12 16 1

8. Isotopes
An isotope is a variation of an element (same protons) but can have diff. # of neutrons
Ex: carbon (atomic mass = )
Carbon (14) and carbon (12) exist in nature

9. Chemical vs. Physical Change
Physical Change: A change that can occur without changing the identity of the substance.
Ex. Solid, Liquid, Gas (Phase change)
Chemical Change: Process by which a substance becomes a new and different substance
Ex. Fire

10. Chemical Reactions
Chemical Reaction: a process in which the physical and chemical properties of the original substance change as new substances with different physical and chemical properties are formed

11. Chemical Reaction Basics
H2 + O2 --> H2O
Reactants
Products
Reactants- substance that enters into a reaction
Products- substance that is produced by a chemical reaction

12. Evidence of Chemical Change
EPOCH is an acronym that stands for evidence that a chemical reaction has occurred.
– Effervescence (bubbles and/or gives off gas)
– Precipitate (solid crystals form)
– Odor (change of smell is detected)
– Color change
– Heat (reaction either heats up or cools down)
Does sighting evidence of a chemical reaction mean that a chemical reaction has undoubtedly taken place? E P O C H

13. Conservation of Mass
Atoms cannot be created or destroyed in a chemical reaction.
What goes in must come out.
So we must balance equations to conserve mass.

14. Balancing Equations Rules: Ex. 2H2 + O2 --> 2H2O
We can not add or subtract subscripts from either side of the equation
We can only add coefficients to the front of each compound
Ex H O2 --> 2H2O
H = H = 4
O= O = 2
Before must match After
See “Balancing Act” worksheet for more examples…