Properties of Matter

Describing Matter Matter exists in one of three states:

◦ Solid◦ Liquid◦ Gas

• All matter is made up of elements or compounds which exist in the form of molecules and atoms

• The spacing between molecules in a substance and the way the molecules move determines the state of the substance

What determines the space? The spacing between molecules is determined by cohesive and adhesive forces

A cohesive force is the term used to describe molecules that are strongly attracted to one another

An adhesive force is the term used to describe the attraction between molecules that are different. They explain why paint sticks or adheres to wood and why oil lubricates a machine

Solids Solids have very strong cohesive forces

The molecules in solids are packed closely together allowing for little movement

This is why solids retain their shape

Liquids• Cohesive forces in liquids are not as strong as in solids so the molecules are further apart and can move

around more

• This extra movement allows liquids to take the shape of their container

• Liquids have strong adhesive forces which allow them to adhere to surfaces

• Oils make good lubricants because of the way they adhere to metal surfaces

• The adhesive force in liquids allows them to act as coolants because they reduce friction

Gases The molecules in gases have almost no cohesive force

Individual molecules are spaced far apart, allowing them more freedom of movement

Because there is little cohesive force in gases, they will expand to fit any container

Mechanical Properties Mechanical Properties describe how a material will behave when it is used in different situations such as supporting a weight or resisting friction

These properties describe how materials like concrete, wood, steel, and glass will react when they are used in mechanical situations including carrying weight

Mechanical Properties of Solids The mechanical properties of solids are different than those of liquids or gases

They include: stress, elasticity, strength, hardness, malleability, ductility, cohesion, adhesion, and tensile strength

We would use these properties to describe the solid

Stress Stress is an important consideration when choosing appropriate building materials in construction

Too much stress results in damage to materials and buildings

The physical effect of stress on materials is called strain and describes how solid materials react to external forces

The four types of external forces that cause stress are tension, compression, shear, and torque

Stress Tension – stretches or pulls materials. It effects the supporting wire cables used in a pulley system on a crane. When a crane lifts a weight, the wires are stretched. If the weight is too heavy, the wires will snap. Over time, the cables are weakened and must be replaced

Compression – shrinks or pushes against materials. For example, the concrete foundation of a building is under constant stress from compression caused by the weight of the floors above

Shear – shifts or cuts materials. Bolts or welds that hold two pieces of metal together experience this type of stress. If the bolts or welds are not strong enough to withstand shear, they will snap. Shear can also cause cracks in materials

Torque – twists or turns materials. For example, moving parts such as drive shafts in heavy equipment are subject to this type of stress. The hoist lines on cranes are subject to torque because of shifts in the weight as it is being lifted and effects of wind

Elasticity Elasticity is described as the ability to return to original shape after subjected to a force such as tension, compression, shear, and torque

A skyscraper can sway several feet in a horizontal direction without damaging its structural integrity

Concrete and steel cores in these buildings help make them more rigid to control heavy swaying

Elasticity – Ultimate Strength The elastic limit of a material describes the maximum limit to which a material can be twisted or bent and still recover its original shape

Ultimate strength describes the point at which material finally breaks.

These two physical properties are important safety considerations

For example, if wire for a crane is stretched beyond its elastic limit, it will deform and have a weak spot. This damage is permanent and the wire must be replaced.

Hardness Hardness describes the material’s ability to resist being damaged

It is associated with durability and abrasion resistance

A harder material is more resistant and durable

Steel and glass are both hard materials that are used in construction of buildings

Malleability Malleability describes the material’s ability to be rolled, bent, or pressed into different shapes

Aluminum and copper are good examples of malleable metals and are often used for architectural features

Think about how easy it is to crush an aluminum can

Brittleness Brittleness is the opposite of malleability

Cast iron and glass are brittle

Cast iron will break or crack if it is bent

Malleability is important in the piping and sheet metal trades

For example, plumbers need to be able to bend pipe to fit into different spaces

Ductility Ductility describes the ability of a material to be stretched into wires or rods

Aluminum, gold, silver, and copper are examples of highly ductile materials

Aluminum can be drawn through a hole to produce a small diameter wire used in welding.

Steel is also highly ductile and is used in the form of steel rods to strengthen concrete. The steels rods and be bent and formed into different shapes

Cohesion Cohesion describes the force of attraction between molecules of the same type

Cohesion is what holds molecules together in solid form

Adhesion is the force of attraction between molecules of different kinds

Tensile Strength Tensile strength depends on cohesive force

It is the force needed to break or pull apart the material

For example, steel has a greater tensile strength than copper. This means it takes a greater force to break or pull apart steel than copper

Tensile strength is measured in PSI (pounds per square inch)

Mechanical Properties of Solids We just learned about stress, elasticity, ultimate strength, hardness, malleability, ductility, cohesion, adhesion, and tensile strength – all mechanical properties of solids

Engineers and architects must consider properties of materials like wood, concrete, steel, iron, and glass because they have different strengths and weaknesses

Building materials are often used in combination to strengthen mechanical properties

Examples Concrete has strong compression and shear mechanical properties, but weak tensile strength

Reinforcing concrete with steel rebar increases the tension for concrete and makes it much more resistant to breaking apart and cracking

The steel bars are placed to carry the tensile stresses

Reinforced concrete is used to make columns, wall footings, and slabs in buildings

Examples Suspension bridges suspend the roadway from huge main cables that extend from one edge of the bridge to the other

The cables rest on top of high towers and are secured at each end by anchors

Most of the weight of the bridge is carried by these cables

The cables are made of thousands of small steel wires that are bound together

Steel is strong under tension. As traffic moves over the bridge, the steel changes shape because of stress and then returns to its normal shape

Mechanical Properties of Liquids Liquids include paints, solvents, coolants, and fuels

Liquids behave differently than solids because the molecules are further apart

The mechanical properties of liquids include: Viscosity, Surface Tension, Buoyancy, Volatility, Cohesion, and Adhesion

Viscosity Viscosity describes how thick a liquid is and how it flows

Viscosity can be used to describe all liquids but it is most commonly used to describe engine oils, paint, and machine lubricants

Heavy equipment such as bobcats and backhoes require different oil viscosities at different temperatures

Colder temperatures require thinner, less viscous oil than that required in summer temperatures

Using the wrong oil could result in damage to the engine and other machine parts

Surface Tension Surface tension describes how the surface of a liquid behaves like a skin that allows certain objects to float

Surface tension can be a good or bad thing

For example, surface tension can stop a liquid from thoroughly wetting a surface.

In hydraulics, oils that bead up on a surface instead of spreading evenly mean uneven wear on surfaces because only part of the surface is being lubricated

Solvents Solvents are used in liquids to reduce viscosity and surface tension

This allows for paint to flow more easily

Reduced surface tension allows paint to coat more easily

Buoyancy Buoyancy is the terms used to describe why objects float in liquids

An object will float if the buoyant force is greater than the weight of the object

This happens because all objects lose a part of their weight when they are submerged in water

In water, we can lift a heavier object than we could in air

This is because the buoyant force of the water lifts the part of the object

Volatility Volatility measures how quickly a liquid vaporizes

A liquid is highly volatile if it changes quickly from a liquid to a gas

The vapours from highly volatile materials can be very dangerous because they are explosive or flammable when the are exposed to heat or air

Gasoline, turpentine, alcohol, and paint thinners are highly volatile

Physical Properties Physical Properties describe characteristics that are part of the material based on the combination of elements that make it up

Electrical conductivity, thermal conductivity, thermal expansion, and corrosion resistance all describe physical properties of matter

Electrical Conductivity Electrical Conductivity describes the ability to conduct an electrical current

Gold, silver, copper, and aluminum are examples of materials that are excellent conductors

Copper and aluminum are commonly used to make electrical wire

Materials that are poor conductors are also important because we use them to insulate

Glass and rubber make poor electrical conductors but they are great insulators

Thermal Conductivity Thermal conductivity measures the rate that heat travels through a material

Welders need to know about this physical property of metal because they must be careful not to overheat it

Overheating metal can change how it will behave under stress.

Thermal Expansion Thermal expansion describes the increase in size of a material when it is heated

Solids, liquids, and gases expand when heated or contract when cooled

Thermal expansion is the reason expansion joints are replaces on bridges

The roadway on a bridge can expand up to a meter in length during the summer

Corrosion Resistance Corrosion resistance describes a material’s ability to resist combining with other elements

Materials react to the environment they are used in

For example, oxidization is the term used to describe rust formation

Rust is probably the most common type of corrosion

The effects of oxidization on other metals like aluminum oxides actually helps to protect the aluminum

Measuring Matter In order to use materials effectively and safely, there must be a way to measure them

Matter – whether in the form of solid, liquid, or gas – is measured using volume, density, and pressure

Volume Volume measures how much space an object takes up or occupies

In the metric system, volume is measured in cubic centimetres (cm³), cubic metres (m³) and litres (L)

In the Imperial system, volume is measured in cubic inches (in³), cubic yards (yd³), quarts, and gallons

Density Density measures the ratio of a mass to a volume

Density compares the masses of equal volumes of different kinds of matter

Density cannot be measured directly. It is calculated after the mass and the volume of the material is known

Density We normally measure density using kg/m³ or g/cm³

When talking about density, we normally compare our objects to water, which has a density of 1 g/cm³

If an object has a lower density than water, it will float

If an object has a higher density than water, it will sink

MassMeasurement of the amount of matter

(or stuff) in an object◦ Measured in grams (g)

There are 3 states of matter:

Solid

Liquid

Gas

VolumeMeasurement of the amount of space an object takes up

◦ Measured in milliliters (ml) or cm3

Which do you think would have the greater volume? The greater mass?

Why?

1 kg of feathers 1 kg of rocks

Density is defined as mass per unit volume. It is a measure of how tightly packed and how heavy the molecules are in an object. Density is the amount of matter within a certain volume.

Density

Which one is more dense?Demonstration: People in a square

How about this: Which square is more dense?

Which one is more dense?

Now which one is more dense?

To find the density

3- Divide Density = Mass g Volume c³

1- Find the mass of the object

2- Find the volume of the object

1- Find the mass of the object

ALWAYS REMEMBER

UNITS!

1) Find the mass of the object

2) Find the volume of the object

3) Divide : Density = Mass - Volume

To find density:

Ex. If the mass of an object is 35 grams and it takes up 7 cm3 of space, calculate the density.

1) Find the mass of the object

2) Find the volume of the object

3) Divide : Density = Mass - Volume

To find density:

Ex. If the mass of an object is 35 grams and it takes up 7 cm3 of space, calculate the density

Set up your density problems like this:

Given: Mass = 35 grams Unknown: Density (g/ cm3) Volume = 7 cm3

Formula: D = M / VSolution: D = 35g/7 cm3

D = 5 g/cm3

Let’s try some density problems together Work on these problems with your neighbor

1 Frank has a paper clip. It has a mass of 9g and a volume of 3cm3. What is its density?

2. Frank also has an eraser. It has a mass of 3g, and a volume of 1cm3. What is its density?

3. Jack has a rock. The rock has a mass of 6g and a volume of 3cm3. What is the density of the rock?

4. Jill has a gel pen. The gel pen has a mass of 8g and a volume of 2cm3. What is the density of the rock?

Change Mass AND Keep Volume Same

Increase the mass increase density

Decrease the mass decrease in density

Which container has more density?

A B

Ways to Affect Density

Change Volume AND Keep Mass Same

Increase the volume decrease density

Decrease the volume increase density

Which container has more density?

A B

Ways to Affect Density

In your notebook illustrate the answer to the following question:

What 2 ways will INCREASE density?

What 2 ways will INCREASE density?

Keep the same mass AND decrease the volume

Keep the same volume AND increase the mass

Liquid Layers

If you pour together liquids that don’t mix and have different densities, they will form liquid layers.

The liquid with the highest density will be on the bottom.

The liquid with the lowest density will be on the top.

Objects or substances with MORE density will sink below objects or substances with LESS density

◦ Which do you think is MORE dense,Water or Oil???

Water, Oil…and a SuperballThe oil is less dense than the water, so it’s on top. The superball is less dense than water, but more dense than oil, so it sinks to the bottom of

the oil layer, yet floats on the top of the water layer.

If you have 2 or more substances,

the MORE dense substance will be on bottomThe LESS dense substance will be on top

The density of five liquids are measured as follows:◦ Liquid 1: 1.0 g/mL◦ Liquid 2: 1.38 g/mL◦ Liquid 3: 0.77 g/mL◦ Liquid 4: 2.95 g/mL◦ Liquid 5: 0.056 g/mL

Draw a picture of all 5 liquids in a test tube how they would layer according to density

Liquid 5

Liquid 3

Liquid 1

Liquid 2

Liquid 4

Liquid LayersCheck out this picture. Which layer has the highest density?

Which layer has the lowest density?

Imagine that the liquids have the following densities: ◦ 10g/cm3. 3g/cm3.◦ 6g/cm3. 5g/cm3.

Which number would go with which layer?

10 g/cm3

3 g/cm3

6 g/cm3

5 g/cm3

Liquid Layers – Try with your neighbor

Which liquid has the highest density?

Which liquid has the lowest density?

Which liquid has the middle density?

Liquid Layers Try on your own!

Imagine that the liquids on the right have the following densities:◦ 15g/cm3 10g/cm3

◦ 3g/cm3 9g/cm3

◦ 7g/cm3 12g/cm3

Match the colors to the correct densities.

3g/cm3

7g/cm3

9g/cm3

10g/cm3

12g/cm3

15g/cm3

ReviewWhat is the formula for density?

What happens if you pour together liquids that have different densities?

Will the liquid on the top have the highest or lowest density?

Will the liquid on the bottom have the highest or lowest density?

Super Scientist Question of the Day

Jake has a book, a ruler, and a balance.

How can Jake find the density of the book with the tools he has?