Chemistry Unit Notes 7th Grade Science

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

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

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

Periodic Table

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

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

Isotopes An isotope is a variation of an element (same protons) but can have diff. # of neutrons Ex: carbon (atomic mass = 12.011) Carbon (14) and carbon (12) exist in nature

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

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

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

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

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.

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. 2H2 + O2 --> 2H2O H = 4 H = 4 O=2 O = 2 Before must match After See “Balancing Act” worksheet for more examples…