8th Grade Science Volume, Lab Safety, & Atoms (8.5ABCDE) Review

Lab Safety

  • Goggles: wear when working with heat, class, chemicals, or when the teacher tells you.
  • Report ALL spills and broken glass to teacher.

Volume

The amount of space an object takes up.

The volume of liquids can easily be determined by using a graduated cylinder.

Liquids in a graduated cylinder show a slight curve at the top. This curve is called the meniscus. To measure the proper volume, you must read it at eye level and at the bottom of the curve.

Regular Objects: volume can be calculated using a formula and a ruler. (L x W xH) The unit for volume of regular objects is cm3.

Irregular Objects: volume can be measure by a method called displacement using water and a graduated cylinder. The unit for measuring a liquid is mL; solid is cm3.

Measure the amount of water in the graduated cylinder that is empty. After object is placed into the cylinder, measure it again. Subtract the two number to determine the volume of the irregular object.

Atomic Structure

  • An Atom is composed of three subatomic particles.
  • Proton
  • Neutron
  • Electron

Mass / Charge / Location
Proton / 1 AMU / (+) / Nucleus
Neutron / 1 AMU / (0) / Nucleus
Electron / 0 AMU / (-) / CLOUD
  • Most of the volume is occupied by empty space found within the electron cloud.
  • Most of the mass is occupied by the nucleus containing protons and neutrons.

Atomic # = Protons = Electrons

Mass # - Atomic # = Neutrons

Models of Sodium Atom

There are many different versions of the Bohr Model. Be prepared to determine the mass (P+N), calculate the # of neutrons (M-A=N), determine the atoms identity (Protons), determine the number of valence electrons (last shell), determine the charge of the atom (remember protons and electrons cancel each other out), determine the charge of the nucleus (always positive).

Notice the model to the far right of the page, it does not tell you how many protons or neutrons it has. If a question tells you to determine the # of protons of the neutral atom, you should know that the number of electrons equals the number of protons.

Valence Electrons: the electrons in the outer most energy level tell us about reactivity (how likely that atom will bond with another).

Electron Cloud

  • 1st Energy Level: holds 2 electrons
  • 2nd Energy Level: holds 8 electrons
  • 3rd Energy Level: holds 18 electrons

Periodic Table

Groups or Families(1-18): Vertical Columns that determine the # of valence electrons an atoms has. Elements in the same group have similar chemical properties, including reactivity.

Periods(1-7): Horizontal Rows determine the # of energy rings an atom has.

Physical Properties

Metals:

  • Luster(shine)
  • Malleable(bendable, can be hammered into sheets)
  • Sonorous
  • Ductile(drawn into wire)
  • Conductors
  • Dense

Nonmetals:

  • Brittle
  • Dull
  • Insulators

Metalloids

  • Shares properties of both metals and nonmetals.
  • Semiconductors

Chemical Properties

All elements have different variations of reactivity determined by the number of valence electrons.

  • Group 1 is the MOST REACTIVE METALS because its outer valence shell only has 1 electron but needs to lose only one to be stable.
  • Group 17 is the MOST REACTIVE NONMETALS because its outer valence shell has 7 valence electrons and needs only one more to be stable.
  • Group 18 is STABLE because their outer valence shells have 8 electrons so they do not react.

Chemistry Language

Element:purest form of a substance.

Examples:

-H

-H2

Molecule: two or more atoms combined in a chemical formula.

Examples:

-H2O

-C6H12O6

-H2

Compound: two or more elements combined in a chemical formula.

Examples:

-H2O

-C6H12O6

Chemical Formulas

6H2O

Coefficient: # of molecules

Subscript: # of atoms

CalallenStudents Pass Staar

Coefficient x Subscript x Parenthesis Subscript

6H2O

Steps for counting atoms:

  1. Check coefficient, add 1 if you do not see it.
  2. Check subscript for every element in formula, add 1 if you do not see it.
  3. Write element symbol
  4. Write expression and calculate

EXAMPLE

6H2O1

H: 6X2 = 12

O: 6X1 = 6

Total = 18

4Al2(S1O3)3

Al: 4X2 = 8

S: 4X1x3 = 12

O: 4X3X3 = 36

Total = 56

Physical Change: when the substance does NOT change, only the form.

Chemical Change: when new substances are formed with new and different properties.

Evidence of Chemical Change:

Our: Odor

Calallen: Color Change

Students: Sound

Love: Light Production

Practicing: Precipitate (solid formation)

Good: Gas Production

Teamwork: Temperature Change (Endothermic: feels cold,

Exothermic: feels warm)