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What's the matter with me? What's the matter with you?!
What's the matter with me? What's the matter with you?!
Matter is the stuff that makes up the physical universe. Matter has 2 defining qualities:
- Matter takes up space, or in other words has volume.
- Matter has mass, which is related to but not the same as weight.
- Matter is made of particles called atoms
Not everything in the universe is made of matter. For example, energy such as light and heat are not made of matter.
States of matter
States of matter
Matter comes in different forms. The 3 main types we will be dealing with in chemistry are solids, liquids, and gases. Most people have experienced all three types. There is one more type plasma, which we will not talk about.
The key differences in states of matter are how the atoms interact with each other and how much energy they have.
Solids have the least amount of energy, resulting in a definite volume and shape. The atoms are tightly held together, but still move slightly by vibrating.
Liquids have more energy than solids, but less than less than gases. Their atoms move around more and are less tightly bound together, but have some cohesion. Liquids have a definite volume, but no definite shape.
Gases have the most energy, and therefore the atoms move the most. The atoms have very little attraction to one another and move 99% independently.
Matter can change states by adding or removing energy.
Mixtures and pure Substances
Mixtures and pure Substances
A pure substance is something made of only one chemical compound. Oxygen is a pure substance made of only one type of atom. Pure substances made of only one atom are called elements. However, pure substances can contain different atoms. For example water is a pure substance that is made of hydrogen and oxygen which are chemically bonded. Pure substances made of more than one atom are called molecules.
A mixture is made of different chemical compounds that are physically mixed together.
There are two types of mixtures:
- homogeneous (hōməˈjēnēəs) mixtures, which are evenly mixed. These mixtures will look uniform like a pure substance, but can be physically separated. Examples include clear solutions, like tea or coffee. Alloys (mixtures of metals) are homogeneous.
- heterogeneous (hedərəˈjēnēəs)mixtures, which are unevenly mixed. You will be able to see the different components of the mixture or it will appear opaque. These mixture will often settle or separate over time. Examples include salad dressing or milk.
Separating Mixtures
Separating Mixtures
Chemists for centuries have used various techniques for separating matter into its basic parts. The most common techniques are:
- Filtration - Used for separating substances in different states of matter such as removing a solid from a liquid. But it cannot be used to separate homogeneous mixtures like solutions.
- Distillation - takes advantage of difference in boiling points of two parts of a solution. The mixture is heated to a temperature in between the boiling points of the two liquids. The liquid with the lower boiling point will change into a gas and rise. Then that gas will be cooled back into a liquid.
- Magnetic separation - used when one part of a mixture is magnetic and one is not
- Centrifugation - spins a sample rapidly and separates based on density.
Chemical vs. Physical Properties
Chemical vs. Physical Properties
A substance's chemical properties are its characteristics in a chemical reaction. Chemical properties can only be observed during a chemical reaction and will change the chemical identity of the substance.
Physical properties are traits of a substance that can be observed without changing its chemical make up. These include:
- appearance/ color
- boiling or melting point
- ability to conduct electricity
- density
- hardness
Extensive properties vary depending on the amount (extent). For example the large an object the more mass it contains.
Intensive properties do not depend on the amount. For example the color of a gold will be the same if there is a large or small amount of it.
Chemical vs. Physical Changes
Chemical vs. Physical Changes
A physical change changes only physical properties but not the chemical identity of a substance. For example chopping a piece of wood in half changes the appearance, but not the identity of the substance. It's still wood. Therefore this is a physical change.
A chemical change changes the chemical identity through a chemical reaction. The substance has it's atoms rearranged into a different material. Burning a piece of wood creates heat, smoke, and ash. These are different substances than wood and therefore are a chemical change.
Indicators of a chemical change
Indicators of a chemical change
A chemical change (reaction) occurs when atoms are rearranged and produce a new substance. It is often difficult to tell whether or not a chemical change has taken place. Here are some clues that we can use to determine if a chemical change has occurred:
- Production of gas (bubbling or fizzing)
- Formation of a precipitate (powder forming in a liquid which makes it look cloudy)
- Change in color
- Change in temperature (transfer heat)
- Change in smell or taste
- Change in volume/ density
- Production of light
Chemical reactions may exhibit one or more of these indicators; however, these are not foolproof signs. Some physical changes like evaporation/condensation or freezing/melting can transfer heat, or produce light, like in light bulbs.
Law of Conservation of Matter
Law of Conservation of Matter
You might think of atoms as the building blocks of our universe. You can make an almost infinite number of creations by rearranging how the blocks are put together. However, these blocks (matter) cannot be created or destroyed. Therefore, you always end with the same number of blocks you started with.
In chemical reactions you always end with the same number of atoms that you started with. The number of carbon (black) atoms, oxygen (red) and hydrogen (white) are the same before and after the reaction. However, you may notice that the atoms have been rearranged.
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