Materials and their structure

. Hypothesis… it is an idea for explaining something

. Theory….. is made from hypothesis has been tested and widely accepted

. Vacuum: means space with no particles. Empty

Particle Theory says:

Matter is made of tiny particles, that are arranged differently in solids,
liquids, gases.

States of Matter
Matter is anything we see or feel. There are 3 states of Matter: They have
different PROPERTIES as they behave differently

SOLIDS
Have a fixed shape
Take the same amount of space and keep same volume
Cannot be compressed or squashed or poured
Particles are fixed and tightly held together.
Particles can vibrate a little but stay in place.

LIQUIDS
Can change shape and they take the shape of the container
They take the same space
Cannot be compressed. Can be poured
Particles are held together weakly. They can move touching each
other

GASES
They fill the container
Volume can change, shape can change
Weight very light
We cannot see or feel them, only smell
Particles are apart from each other, they spread out
Solid

Liquid

Gas
Change of State

- Evaporation …… Liquid to Gas:

when a liquid is heated it evaporates.
The particles in liquids are held weakly , so heat moves them more, and
can break and escape.
water boils at 100 degree, turns into steam, its called “boiling point”

- Condensing …… Gas to Liquid:

When a gas cools it condenses to form a liquid. When a gas touches a cold
surface the heat transfers to it. Then particles move less and get closer,
becoming liquid.

- Melting …… Solid to Liquid:

the temperature needed is called “melting point”

Heating Solids: Solids expand as heat energy is transferred to the

particles and make them vibrate. The more heat, more vibration and
bigger they get.

If we heat SOLIDS strongly they MELT, turning liquid, because heat makes
particles vibrate so much that bonding between particles gets weak, and
cannot hold them in a patern. The particles start moving.

- Freezing …… Liquid to Solid:

Liquid becomes solid when freezes. Like water to ice. When a liquids
looses heat its particles loose energy and move slower until they stop
moving. Now they only vibrate, and become like a solif.

Volume
Volume of liquid is measured with a measuring cylinder. The curve formed
at the top is called meniscus

Temperature
We use a thermometer. Its liquid rises with heat and we read its scale

Water Cycle
Water is vital for life. Our bodies are 60% water.
Water on earth is always moving between rivers, lakes, oceans, atmosphere and
land. It is recycled continuously for millions of years.
1. Water moves to the atmosphere
The Sun heats the earth, and with enough heat energy some water
particles break down and get free so some water evaporates and goes up.
Water also evaporates from plants to the atmosphere “transpiration “

2. Water in the atmosphere cools down.

As water in the air cools its particles loose energy and cannot move, so
water condenses forming droplets that make clouds.
Air moves the clouds around the world.

3. Water falls from clouds

When lot of water condenses it gets heavy and air cannot hold it. The
droplets fall back as rain.
“Precipitation”..: if drops get very cold they make snow.

4. Water falls on earth

Water collects in river, lakes and oceans. Soon it will evaporate and water
cycle will start again.
If it falls on plants, it can enter the ground feeding the roots, or also go
back to the air from the leaves.

5. Ground water
Water that enters the ground and rocks forming groundwater. Some will
move to rivers, some will store under the ground.
Glaciers form in cold seasons and when they melt water also enters the
ground or go to rivers.
..”surface run-off”….Ground water surfaces and flows direct into rivers or
oceans. When they carry soil they can block rivers
Particles

Why a balloon deflates

A balloon’s air seems to escape because its skin has millions of holes so tiny
that molecules of inner air can escape through them. This is how the balloon
deflates.

What is diffusion

Particles

Why a balloon deflates

A balloon’s air seems to escape because its skin has millions of holes so tiny
that molecules of inner air can escape through them. This is how the balloon
deflates.

What is diffusion
Diffusion means one substance spreading through another.

For example, when we open a perfume, its molecules spread around the room
and collide with moving air particles.

Why gases expand more than solids

Gas molecules are already expanded which makes attraction among them
weaker. On the other hand, molecules in solids are close to each other thus less
expandable.

How air pressure keeps a balloon inflated

When air molecules are blown into a balloon through breath, they move around
rapidly. When they hit the walls they push and millions of small pushes become
air pressure.

When the balloon is inflated where is the air pressure highest?

Inside it, because it is a small space with millions of tiny air molecules moving
rapidly.

Solid

Liquid

Gas
Element, Compound and Mixture

What is an element. Why is carbon called Element

An Element is a chemical substance that cannot be broken into anything similar.
That is because it is made up of only one type.

Carbon is an Element because it is made up of carbon atoms only

Describe an ATOM
An atom is the smallest part of an element that can exist and take part is a
chemical reaction. Atoms are far too small to see with an ordinary microscope.
Their size can differ depending on the chemical element. (e.g., Gold atoms are
bigger than hydrogen atoms)

Name 3 parts of an atom

Except the Hydrogen atom, all atoms are made of 3 smaller particles,

Protons – They have a positive charge (+ve)

Neutrons – These have No charge. They are neutral

Electrons – These have negative charge (-ve)

Why is Carbon Dioxide a good gas for fire extinction?
Carbon Dioxide is denser than air and settles down over the fire putting it off

Why is Liquid Nitrogen used to freeze food?

It does not burn or let things burn in it. Does not react with other elements
easily.
It is cold and freezes food fast.

Why is Argon used in light?

It is used for filling light bulbs. The argon filament surrounding the bulb can get
very hot without burning. It also does not allow other things to burn in it.

Difference between Physical and Chemical change

Physical Change,
No new substances ae made and the change is usually reversible

Chemical Change,
A new substance is made and the change is normally difficult to reverse

Metals vs Non-Metals,

Metals Non-Metals

Dense and feel Heavy Not very Dense and feel Light

Shiny appearance when polished Dull appearance

High boiling point Raw boiling point

Difficult to melt usually gases or solids which melt easily

Malleable (can be bent) Brittle or powdery

Forces and their effects

What is force, what is its measuring Unit and how do we call its
measuring meter
A force is a push or pull upon an object that causes changes on its state.
The measuring unit is Newton (N)
The measuring meter is Newton meter

What is density. What means that water has a density of 1g/cm3.

Density is equal to Mass/Volume.

The unit used is g/cm3 or Km/m3.

For example, Lead has higher density than wood because it has more mass in
every cm.

Water Density is 1g/cm3;

If an object has lower density than water, it will float. If it has higher density it
will sink.

The denser the liquid the greater the upthurst: Ships float higher in sea water
than in fresh water, because sea water is denser.

What is Air Resistance

It is a force formed by Air molecules bumping each other.

Why objects float or sink in water?

Because of the object density. If an object has lower density than water, it will
float. If it has higher density it will sink. Water Density is 1g/cm3;

W= m x g
means Weight = Mass x Gravity

Q. A robot of 100 kg mass is built on earth where gravity is 9.8/kg.

If the robot goes to Mars, where gravity is 3.7/kg what is the robot’s weight
on both places:

Weight on Earth:
W=mxg
W = 100 x 9.8
W = 980 N
Weight on Mars:
W=mxg
W = 100 x 3.7
W = 370 N
The solar system

What is a day
The Earth spins on an axis through the North and South Poles.
One complete rotation of the Earth takes 1 day or 24 h to complete (23.93 h
actually)

What is a year
The Earth revolves around the Sun. One Orbit takes around 365.25 days or 1
year to complete. Since 365.25 is not a round figure, an extra day is produced
every 4 years on February 29th in order to adjust the calendar year with the solar
year, and this will be called a Leap year.

What is an eclipse
When a planet or the moon block off light from another, an eclipse takes place
There are 2 types of eclipse, SOLAR and LUNAR