Matter can be classified into atoms, elements, compounds, and mixtures.
An atom is the smallest unit of matter that still keeps the properties of an element.
An element is a pure substance made from only one type of atom.
For example, oxygen gas is an element because it only contains oxygen atoms.
A compound is made when two or more different elements are chemically bonded together in a fixed ratio.
Water is a compound because hydrogen and oxygen are bonded together.
A mixture contains two or more substances, but they are not chemically bonded.
Salt water is a good example because it contains water and salt mixed together.
So the key idea is this:
elements and compounds are pure substances, but mixtures can be separated by physical methods.
Filtration is used to separate an insoluble solid from a liquid.
The mixture is poured through filter paper inside a funnel.
The liquid passes through the filter paper and collects in the flask below.
This liquid is called the filtrate.
The insoluble solid cannot pass through the filter paper, so it stays behind.
This solid is called the residue.
A simple example is separating sand from water.
The sand stays on the filter paper, while the water passes through.
So remember:
filtration works when one substance is insoluble in the liquid.
The residue is the solid left behind, and the filtrate is the liquid collected underneath.
Distillation is used to obtain a pure solvent from a mixture.
The mixture is heated, and the substance with the lower boiling point evaporates first.
The vapor then travels into the condenser.
Inside the condenser, cold water cools the vapor down.
As it cools, the vapor condenses back into a liquid.
This pure liquid is collected in the receiving flask.
Any non-volatile impurities, or substances with much higher boiling points, stay behind in the original flask.
It is especially useful when we want to collect a pure liquid from a solution.
This screen shows two important laboratory techniques.
First, a separatory funnel is used to separate immiscible liquids.
Immiscible means the liquids do not mix together.
For example, oil and water form two separate layers.
The denser liquid stays at the bottom, and the less dense liquid stays on top.
By opening the tap carefully, we can drain the bottom layer first.
The second technique is melting point determination.
A pure substance usually melts at a sharp temperature.
An impure substance melts over a wider temperature range, and often at a lower temperature.
So a melting point test can help identify a substance and check its purity.
Kinetic molecular theory explains matter by looking at particles and their movement.
The main idea is that particles are always moving.
In a solid, particles are packed closely together and only vibrate in fixed positions.
In a liquid, particles are still close together, but they can move past each other.
In a gas, particles are far apart and move quickly in random directions.
Temperature is connected to kinetic energy.
When temperature increases, particles move faster.
When temperature decreases, particles move more slowly.
So the state of matter depends on particle movement, particle spacing, and the strength of attraction between particles.
This model helps explain solids, liquids, gases, and changes of state.
This screen shows how substances change state when energy is added or removed.
When a solid is heated, its particles gain energy and vibrate more.
Eventually, the solid melts and becomes a liquid.
If heating continues, the liquid boils and becomes a gas.
On a heating curve, temperature rises when the substance is in one state.
But during melting or boiling, the temperature stays constant.
This flat part of the graph is called a plateau.
During a plateau, energy is not raising the temperature.
Instead, the energy is used to overcome attractions between particles.
So the key idea is this:
during a change of state, temperature stays the same even though energy is still being added.
In a gas, not all particles move at the same speed.
Some particles move slowly, some move at medium speed, and some move very fast.
The Maxwell-Boltzmann distribution shows the range of molecular speeds in a gas.
When temperature increases, particles have more kinetic energy.
So more particles move at higher speeds.
The graph shifts to the right and becomes wider.
This idea also helps explain evaporation.
Even below the boiling point, some fast-moving particles at the surface can escape from the liquid.
At higher temperature, more particles have enough energy to escape.
So the key idea is:
higher temperature means faster particles and a wider range of molecular speeds.