Chemistry Unit Notes7th 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 ParticlesSub-Atomic Particles

Part of Part of AtomAtom

ChargeCharge LocationLocation Mass/SizeMass/Size

ElectronElectron - negative- negative outside outside nucleusnucleus

.0006 amu.0006 amu(too little to (too little to count)count)

ProtonProton + positive+ positive inside inside nucleusnucleus

1 amu1 amu

NeutronNeutron no chargeno charge inside inside nucleusnucleus

1 amu1 amu

Periodic Table

Using the Periodic Table Atomic NumberAtomic Number

– Equal to # protons = # electronsEqual to # protons = # electrons– Periodic Table is arranged by this Periodic Table is arranged by this

numbernumber

Symbol Symbol – ““ShorthandShorthand”” for the element – Note 2 for the element – Note 2ndnd

letter is always lowercaseletter is always lowercase

Atomic Mass NumberAtomic Mass Number – Total AVERAGE mass of Protons + Total AVERAGE mass of Protons +

Neutrons + ElectronsNeutrons + Electrons

17

Cl

35.5

More PracticeMore Practice

Determine the name, number of Determine the name, number of protons, neutrons and electrons for protons, neutrons and electrons for each element shown and draw…each element shown and draw…

1

H

1

8

O

16

6

C

12

IsotopesIsotopes

An isotope is a variation of an An isotope is a variation of an element (same protons) but can element (same protons) but can have diff. # of neutronshave diff. # of neutrons

Ex: carbon (atomic mass = Ex: carbon (atomic mass = 12.011)12.011)– Carbon (14) and carbon (12) exist in Carbon (14) and carbon (12) exist in

nature 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 ReactionsChemical Reactions

Chemical Reaction:Chemical Reaction: a process in a process in which the physical which the physical andand chemical chemical properties of the original substance properties of the original substance changechange as new substances with as new substances with different physical and chemical different physical and chemical properties are formedproperties are formed

Chemical Reaction BasicsChemical Reaction Basics

H2 + O2 --> H2O

Reactants- substance that enters into a reaction

Products- substance that is produced by a chemical reaction

Reactants Products

Evidence of Chemical Evidence of Chemical ChangeChange

EPOCH is an acronym that stands for evidence EPOCH is an acronym that stands for evidence that a chemical reaction has occurred.that a chemical reaction has occurred.

– – Effervescence (bubbles and/or gives off Effervescence (bubbles and/or gives off gas)gas)

– – Precipitate (solid crystals form)Precipitate (solid crystals form) – – Odor (change of smell is detected)Odor (change of smell is detected) – – Color changeColor change – – Heat (reaction either heats up or cools Heat (reaction either heats up or cools

down)down)

Does sighting evidence of a chemical reaction mean Does sighting evidence of a chemical reaction mean that a chemical reaction has undoubtedly taken place?that a chemical reaction has undoubtedly taken place?

EEP P OO

CCHH

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: 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…