What are chemists?
Chemists specialize in matter:
- what it is
- how one kind differs form another
- what different kinds have in common
- how one kind can be changed to another
- how it can be kept the same
Water is one of the most familiar kinds of matter. The temperature at which matter changes from a liquid to a gas is called boiling point.
A mixture is two or more kinds of matter that have separate identities. It is easily separated into component parts, and some people say it is impure.
Mixtures can be heterogeneous mixtures or homogeneous mixtures.
Heterogeneous mixtures- the substances in the kind of a mixture are not spread out evenly.
Example: Salad Dressing
Homogeneous mixtures- the substances are spread evenly throughout, a homogeneous mixture is called a solution.
Example: Vinegar
By adding things to pure water, you can quickly find that there are no mixtures that do not scatter light.
If table salt is added, it disappears. You can taste it, but it cannot be seen.
Therefore, the table salt does not scatter light.
Therefore, the table salt does not scatter light.
Solutions - mixtures that look uniform throughout and do not scatter light.
Distillation - separates most mixtures.
Mixtures that CAN be separated:
- household ammonia
- alcoholic beverages - for example, whiskey
Pure Substances have a constant boiling point. Mixtures ordinarily do not.
Freezing Point - the temperature at which a liquid changes to a solid
Melting Point - the temperature at which a solid changes to a liquid
Density - a property of matter that describes its mass per unit volume
Chemical Changes - changes that produce a new kind of matter with different properties
Physical Changes - changes that change the appearance, but do not produce new kinds of matter
Decomposition - when one kind of matter comes apart (decomposes) to form two or more kinds of matter
Electrolysis - involves passing an electric current through a substance, causing it to decompose into new kinds of matter
The Law of Definite Composition: A compound always contains two or more elements combined in a definite proportion by mass
The Law of Multiple Proportions: The fact that two or more compounds with different proportions of the same elements can be made.
Check out this video called the Atom Song!
Skip to 30 seconds to get to the song.
The Atom Song!
Summarizing for you a part of the reading (36-39) from the textbook:
The general idea here is that matter is made of atoms.
The idea that matter is made of atoms did not become popular until the early 1800s.
Now, lets look at some terms:
Atom: The smallest possible piece of something, they vary in size and mass
Elements: Pure substances that cannot be broken down
Solid: Holds its shape since atoms are stuck together
Liquid: The temperature is increased and atoms will vibrate and flow past one another
Molecule: particles made up of more than one atom
Compounds: Made by combining elements in definite proportions (made of 2 or more types of atoms)
Ions: particles that have an electrical charge
Ionic: melt to form ions
Molecular: melt as molecules
A very large water molecule
A caffeine molecule
LSD (acid) molecule. Don't try this at home kids!
My Socials Teacher once told me that once you know the meaning of the terms, it makes the material much easier to learn. So hopefully this helps!
Here's a cool video about atoms and molecules, and the guy talking has braces! It's pretty funny.
Click here
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