# BC Science 8 Chapter 7

BC Science 8 – Chapter 7

7.1 States of Matter

§  Matter - is anything that has mass and

volume

§  Mass - is the quantity of matter that a

substance or object contains, and is usually measured in grams

§  Volume - is the amount of space taken up by

a substance or object

3 States of Matter

§  Solid - is the state of matter that has a

definite shape and volume (ex. a

bowling ball)

§  Liquid - is the state of matter that has a

definite volume, but its shape is

determined by its surroundings (ex.

water in a beaker)

§  Gas - is the state of matter that has its

shape determined by its

surroundings (ex. helium in a

balloon)

The Particle Model of Matter

1.  All matter is made up of very small particles. The particles are much too small to observe with the naked eye or with a light microscope.

2.  There are spaces between the particles. The amount of space between the particles is different for different states of matter. (ex. gases have more space between particles than solids do)

3.  The particles that make up matter are always moving.

4.  The particles are attracted to one another. The strength of the attraction depends on the type of particle.

Diagram on pg 248

The Kinetic Molecular Theory

1.  All matter is made up of very small particles (atoms and molecules)

2.  There is empty space between particles.

3.  Particles are constantly moving. The particles are colliding with each each other and the walls of their container.

(a) Particles of a solid are so tightly packed together they can’t move around freely….they can only vibrate

(b) Particles of a liquid are farther apart and they can

move by sliding past each other

(c) Particles of a gas are very far apart and they move around quickly.

4. Energy makes particles move. The more energy the particles have, the faster they can move and the farther apart they can get.

§  Kinetic Energy - is the energy of motion

- all particles in every solid, liquid, and gas are always moving, so they have kinetic energy

Thermal Expansion and Contraction

§  Thermal Expansion - When energy is added to matter,

you increase the kinetic energy of the particles. (the temperature rises when you add heat, causing the particles to move faster, increasing their volume)

Any kind of matter expands when its temperature increases (thermal expansion)

§  Thermal Contraction - is a decrease in the volume of

something when its temperature

drops

-  When the temperature decreases, the movement of particles slow down, taking up less space as they lose energy, the matter contracts, or decreases in volume

Diagram 7.3A-C

§  Thermal Energy - is the total amount of energy of

particles making up a substance

§  Heat - is the energy transferred from one

material or object to another as a

result of a difference in

temperature or a change in state

§  Temperature - a measure of the average kinetic

energy of the particles in a

substance

Changes of State

§  Melting - is the change of state of a

substance from a solid form to

liquid form

§  Evaporation - is the change of state of a

substance from liquid form to gas

form

§  Condensation - is the change of state of a

substance from gas form to liquid

form

§  Solidification - is the change of state of a substance

from liquid form to solid form

§  Sublimation - is the change of state of a substance

from solid form to gas form

§  Deposition - is the change of state of a substance

from gas directly to solid without

forming a liquid (ex. frost forming

on a window on very cold days)

§  Melting Point - is the temperature at which a solid

turns to a liquid

§  Boiling Point - is the temperature at which a liquid

turns to gas

pg 99 table

Diagram 7.5A

§  Permafrost - is the ground that remains at a

temperature below freezing all

year long

7.2 Fluids and Density

§  Fluids - is any form of matter that can flow

(liquids and gases flow not solids)

§  Density - is the amount of mass that is

contained in a certain volume of a

material

- describes how closely packed

together the particles are in a

material

-  the key to density is the spacing of the particles in a material

-  particles of gas are spaced very

far apart, particles of liquid are

spaced much closer together

-  most substances are denser in their

solid form (except water)

-  when water freezes, the particles

move slightly farther apart as they

become fixed in position

Layers of Fluids

§  When you compare the masses of equal volumes of different kinds of matter, you are comparing their densities.

§  Some liquids float on top of other. Liquids will layer in order of density.

The less dense liquid floats on the denser liquid if the two liquids do not mix together. (ex. corn syrup and water – water will float on top)

§  Differences in air density contribute to weather. When air is heated near the ground on a hot day, the particles gain energy and move farther apart. The warm air has a lower density than the air around it, the warm air then rises, cooler air rushes in beneath it, and a breeze is created.

§  Air is a mixture of mostly nitrogen and oxygen. Air particles are denser close to the Earth’s surface. An increase in altitude means the farther apart the air particles are spread out, and the air density is lower.

Measuring Density

§  To find the density of a substance you need to know its mass and its volume.

§  Mass can be determined using an electronic scale or balance.

§  Volume of a solid is measured in cubic centimeters (cm 3). A cubic centimeter is the volume of a cube that measures 1 cm on each side. (The volume of an object equals the number of 1 cm cubes it takes to fill that object)

pg. 105

Calculating Density

When you know the mass and volume of a substance, you can calculate the density.

§  Density equals the mass of something divided by its volume.

Density (D) = mass (m) or D = m

Volume (v) V

§  The mass units for solids, liquids, and gas are grams (g) or kilograms

(kg)

§  The density of fluids is usually measured in g/mL (ex. 155 mL sample of glycerol is placed on a scale and records a mass of 195 g.

This is a mass-to-volume ratio of 195 g: 155 mL

195 g = 1.26 g/mL

155 mL

§  The density of solids is measured in g/cm3

Displacement

§  Displacement is the amount of space that an object takes up when placed in a fluid.

§  By measuring the displacement of an object, you can measure the volume of the object.

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Eric Hamber Secondary

BC Science 8 – Chapter 7

Kinetic Molecular Theory explains the

Characteristics of Solids, Liquids, and Gases