Science notes

Science Notes

8th Grade

Semester 1

8th Grade

Unit 1

Semester 1

Inquiry

The act of asking or looking for information

Interactive

Something where the steps are repeated making improvements along the way

Controlled Experiment

An experiment in which only one variable is altered or changed in the experiment’s
set up and all other variables remain the same between different groups

Independent Variable

The manipulated variable; the variable that is different for different groups when
you set up the experiment

Dependent Variable

The responding variable; the variable that you are keeping track of and measuring
throughout the experiment

Controlled Variables

Variables that are the same between all control groups and experimental groups;
also called constants

Unit 2

Semester 1

Accuracy

The closeness of a measured to a standard or the true value

Precision

The closeness of two or more measurements to each other

Significant Digits Rules

1.Non-zero digits are always significant

15.78g 4 sigfigs

2.Any zeros between two significant digits are significant

1005 4 sigfigs

3.Trailing zeros after significant digits that are not between significant digits are significant

1.000 4 sigfigs

4.Trailing zeros with decimals points at the end are significant

1000. 4 sigfigs

5.Trailing zeros without decimals are not significant

15480000 4 sigfigs

6.Zeros at the front of a measurement are not significant

0.007789 4sigfigs

7.Exponents in scientific notation are significant

2.700 cm x 10^-4 4 sigfig

Unit 3

Semester 1

Mixtures

●Each substance in a mixture retains its own properties

●Mixtures can be separated by physical means

Suspension

●Heterogenous mixture containing solid particles that are sufficiently large for
sedimentation

●Can be filtered with filter paper

Colloids

●Between a solution and suspension for particle size

●Homogenous

●Scatters in light (called the tydnall effect)

Types of Colloids

●Foams

-A gas dispersed into a liquid Ex: Whipped cream, shaving cream

-A gas dispersed into a solid Ex: Marshmallow

●Emulsion

-A liquid dispersed into a liquid Ex: Milk, mayonnaise, hand cream

●Aerosols

-A liquid dispersed into a gas Ex: Fog, mist, hair sparys

●Smoke

-A solid dispersed into a gas Ex: Smoke, air particulates

●Sols

-A solid dispersed into liquid Ex: Pigmented ink, blood, paint

●Gels

-Can hold a large amount of water

-Viscous gelatinous body that coagulates(usally water) Ex: Agar, gelatin, jelly

Characteristics of Solutions

●Small particle size

●Homogenous mixture

●Solution does not allow beam of light to scatter

●Solutions are stable

●The solute from the solution cannot be separated by filtration

●The particles of solute in solution cannot be seen by the human eye

Parts of a Solution

●Solvent

-The part with the greater amount

●Solute

-The part(s) with the lesser amount

Solubility

The amount to solute that can dissolve ina given amount of solvent

Increasing rate at which substance dissolves

Solubility increases …

Through the number of particles through
agitation(stirring/shaking)

Through the number of particles by increasing
surface area through crushing

Solubility increases …

Kinetic energy which increase temperature

Kinetic energy by agitation(stirring/shaking)

Solubility Curve

●What the mass a solute will dissolve at 100g(or 100mL) of water over a range
of temperatures

●Water solutions are known as aqueous solutions

Saturated

The maximum amount of a salute that a solute will dissolve at a specific
temperature under normal conditions

Unsaturated

When more solution can be dissolved at that temperature

Supersaturated

Holds more that holds more solute that can normally dissolve in that volume the
solvent

Solubility Graph

Unit 4

Semester 1

Democritus

●460-370 BC

●Greek philosopher

●Concept of the atom

●Our english word “atom” comes from a Greek word “atomos” meaning the
smallest unit of matter

●Atom, was irreducible and indestructible

●Everything in the universe was composed of indivisible atoms

●Infinite number of atoms

Aristotle

●350 BC

●4 elements water, earth, air, fire

●Theory was wrong lasted for 2000 years

Dalton

●1766-1844

●Worked on weather, gas law, atomic weights

●Theory started at lecture in Royal institute

●Elements are made of atoms

●Atoms of the same elements have the same size atoms but different from
other elements

●Atoms can not be divided, created, or destoryed

●Atoms of different elements combine to form simple whole ratios to make
chemical compounds

●During chemical reactions atoms are combined, separated, or rearranged

Thomson

●1856-1940(most work done in 1890’s)

●Negative particles he called corpuscles(electrons)

●Corpuscle have mass and charge

●Corpuscle exist in all atoms

●Cathode ray

●Plum pudding model

Rutherford

●1817-1937

●Theory made in 1911

●Added nucleus to the atom

●Gold foil experiment

Bohr

●1885-1962

●Publsihed work in 1913

●Won a noble prize and so did his son

●Combined experiments and observations into one explanation

●Electron orbits nucleus

●Electron magnetic waves can only occur when an electron jumps from one
orbit to another

●Energy levels

Parts of Atom

Particle Relative Mass Relative charge Symbol Location

Proton 1 +1 p+ Nucleus

Neutron 1 0 n0 Nucleus

Electron 1/1840 -1 e- Electron cloud

Protons

●Each element has a different number of protons

●Determine the type of element

Neutrons

●Mass slightly larger than Proton

●Discovered on 1932

●Helps keep the Nucleus stable

Atomic number

Number of protons

Mass number

Number of Proton and Neutrons

Isotopes

Atoms with the same number of Protons but a different number or Neutrons

Formulas

Atomic number = #p+ = #e-

Mass number = #p+ +#e-

Dmitri Meneleev

●First to widely recognize the periodic table

●Arranged by atomic mass and properties

Henry Moseley

●Observed and measured the x-rays of metal crystals

●Found that you could determine the number of Protons in an element

●November 23, 1887 - August 10, 1915

Periodic Table

●Arranged by properties and atomic number

●Predicited new elements

●Vertical column called famillies or groups

●Horizontal rows are called periods

Bohrs Energy Levels

●1st energy level holds 2 electrons

●2nd energy level holds 8 electrons

●3rd energy level holds 18 electrons

●4th energy level holds 32 electrons

Subatomic Particles

A particle smaller than an atom Proton, Neutrons, Electron

Nucleus

The center of an atom that contains Protons and Neutrons has the most mass of
the entire atom

Average Atomic Mass

The weighted average mass of naturally occurring isotopes of each element

Alpha Particle

Radioactive particle made of two Protons and two Neutrons repelled by other
positively charged particles

James Chadwick

Used radioactivity to prove neutral charge (Neutron)

Semester 2

8th Grade

Unit 7

Semester 2

Motion Diagram

A model of how an object moves by showing its position at various equally spaced
amounts of time

Reference Point

The starting point you choose to describe the location/postion and motion of an
object in comparison to; sometimes referred to a reference frame

Position (x)

An object’s distance in a certain direction from a reference point

Distance (d)

The total path an object has traveled given its ending position

Displacement (Δd)

The distance between the initial position and the final position of an object; the
distance and direction an object has moved