Chemical Building Blocks

Chapter 2 – Solids Liquids and Gases

Section 1 – States of Matter

Vocabulary

Solid Crystalline solid Amorphous solid Liquid Fluid Surface tension Viscosity gas

States of Matter

Our world is full of substances that can be defined as being one of the three primary states of matter Solids, liquids and gases

Solids, liquids or gases can be elements, compounds or mixtures.

Air is a mixture of gases, but is made from elemental gases.

To truly define a solid, liquid or gas, we must look at their properties.

Solids

If I pick up a rock, and just move it around the room, will it change shape?

If I take it outside right now, will it change shape?

Will it become bigger if I put it in a bowl? No. A solid has a definite shape and a definite

volume. This means it will keep its shape and volume

in any position and in any container.

Particles in a solid

The particles in a solid are packed very close together.

Also, tightly fixed in one position.

The particles are NOT motionless, but because of the tight packing, they vibrate back and forth only a little bit.

All students in the hallway.

Types of solids If in the solid, the particles form a regular,

repeating pattern, crystals form. Solids that are made up of crystals are called

crystalline solids. Salt, sugar, snow are examples Always will melt at a specific temperature

In amorphous solids, the particles are not arranged in a regular pattern. Plastics, rubber, butter, and glass are examples. Does not melt at a distinct temperature, instead,

may become softer or change into a new substance when heated.

Picture of a crystalline solid

Liquids

Liquids have a definite volume, but no shape of its own.

This means if I have 100 mL of a liquid, and pour it into a new container, I will still have 100 mL, but it may be shaped differently.

Particles in a liquid

Particles packed ALMOST as tightly as in a solid, but not as close.

Particles can move around each other freely. Usually in contact, but allows motion to occur. Since particles can move around freely,

liquids can move around (flow). A liquid is a fluid, which is a substance which

can flow.

Properties of Liquids

Surface tension is the result of an inward pull around the molecules of a liquid that keep them together. Is why water forms droplets that bead up on a

surface Allows insects to “walk” on water.

Viscosity is a liquids resistance to flowing. Viscous liquids don’t flow much at all Low-viscosity liquids flow easy.

Gases

Gases are fluids, like liquids. How does breathing show that gases are

fluids? However, a gas has no set volume, or shape. A gas will fill up whatever space it can. Gas particles stay apart from each other, and

move around a LOT. Because they move around a lot, they fill up

whatever space they can!

Chemical Building Blocks

2.2 – Changes of State

Vocabulary

Melting Melting point Freezing Vaporization

Evaporation Boiling Boiling Point Condensation Sublimation

Physical State and Temperature

Remember, particles of a substance with higher temperature have higher thermal energy.

Thermal energy ALWAYS moves from warmer substance to cooler substance.

Particles of a liquid have more thermal energy than particles of the same substance in solid form.

As a gas, has even more thermal energy.

Changes between solid & liquid

Change of state from solid to a liquid is called melting.

This involves an increase in thermal energy. In most pure substances, melting occurs at a

specific temperature called the melting point.

Melting point often used to identify a substance.

What is Happening

Melting Increased thermal energy Particles move faster, more Faster moving particles = higher temperature Eventually, move enough to separate from each

other enough to become a liquid At the melting point, the particles of a solid

substance are vibrating so fast they break free from their fixed positions.

Freezing

When freezing, the reverse of melting occurs Loses thermal energy Particles slow down Temperature decreases At freezing temperature, the particles of the liquid

are moving so slowly they begin to form regular patterns (i.e. solid!)

Melting and freezing temperature are the same thing!

Changing Between Liquid and Gas

The change from liquid to gas is called vaporization.

Vaporization takes place when the particles in a liquid gain enough energy to form a gas.

There are two main types of vaporization Evaporation Boiling

Evaporation

Evaporation is vaporization that takes place at the surface of a liquid. Shrinking puddle is an example Water in puddle gains energy. The added energy allows SOME of the water

molecules on the surface to escape into the air. Or, evaporate.

Boiling Boiling occurs when a liquid changes to gas below

the surface as well as at the surface. You see the results as bubbles form. The temperature at which a liquid boils is called its

boiling point. As you heat up the liquid

Thermal energy increases Particles move faster Temperature increases At boiling point temperature, particles have enough energy

to move away from each other enough to be a gas.

Also used to identify an unknown substance.

Boiling Point and Air Pressure

Boiling point depends on the amount of air pressure.

The less air pressure, less energy is needed for the particles to escape into the air.

Less energy needed = lower boiling point. In Denver, CO, water boils at 95°C, not

100°C like at sea level.

Condensation

The opposite of vaporization Condensation occurs when a substances

changes from a gas to a liquid. The particles in the gas must lose thermal

energy for this to happen. Water vapor is impossible to see. When you see steam, really seeing the tiny

droplets of water suspended in the air.

Changes Between Solid and Gas

It happens! Sublimation occurs when the surface

particles of a substance gain enough energy to form a gas.

During sublimation, particles do NOT pass through the liquid state to form a gas.

Chemical Building Blocks

2.3 – Gas Behavior

Vocabulary

Pressure Boyle’s Law Charles’ Law

Measuring Gases

Whenever we deal with something, like to be able to measure it in some way. Making quantitative measurements

When we work with a gas, we want to know three things Volume Temperature Pressure

Volume of gasses

Already discussed volume in previous chapter

Because gas particles fill up any available space, volume of gas = volume of container.

Temperature of gasses

Remember: Temperature is the measure of the average energy of particles moving in a substance. Faster particles = higher temperature At room temperature (20°C), the average gas

particles moves at 500 meters per second (more than 2x cruising speed of jet airplane).

Pressure

Pressure is a force (push) divided by area being pushed. Or, Pressure = Force / Area Difference between sharp and dull knife. Which

would have more pressure? With a gas, pressure is the force of its

outward push divided by the area of the walls of the container.

Measured in units of pascals (Pa) or kilopascals (kPa) (1 kPa = 1000 Pa)

The “firmness” of a gas-filled object comes from the pressure of the gas. “Firmer” objects have higher pressure

Higher pressure is due to a greater concentration of particles inside the gas-filled object.

If a hole is punched in the container, particles will leave the higher-concentration area to go to the lower-concentration area.

Pressure & Volume

Bag demonstration As I push bag, what happens to volume? What happens to firmness of the bag?

Boyle’s Law states that when the pressure of the gas at constant temperature is increased, the volume of the gas decreases.

What does this mean if the pressure is decreased?

Relates pressure to volume.

Weather balloons High altitude weather balloons float because of

helium gas inside of them. High altitude = low pressure What would happen to the balloon if they filled it

up all the way on the ground?

Pressure and Temperature

Remember, the faster particles are moving means the higher the temperature is.

Faster moving = hitting walls of container more often.

Hitting walls of container more often = Higher pressure

When the temperature of a gas at a constant volume is increased, the pressure also increases.

Truck-driver tires.

Volume and Temperature

Charles’ Law brings these together. Higher volume = higher temperature (for a constant pressure).