Introduction to Chemistry

chem·is·try /ˈkemistrē/NounThe branch of science that deals with the identification of the

substances of which matter is composed; the investigation of their properties and the ways in which they interact, combine, and change; and the use of these processes to form new substances

(starting out with a definition is so cliché. I suggest not doing it in essays)

Physical vs Chemical PropertiesPhysical: anything that describes the substance as is, without changing it into a new substance

Density Color

Boiling Point Electrical conductivity

Malleability And many more....

Chemical: describes how a substance reacts—changes into other substances

Busts into flame on contact with waterReacts with acid Decomposes into salt and oxygen

Physical vs Chemical Changes“Is it still the same substance when I'm done with it?”

Physical changes: Yes!Boiling Cutting

Smashing

Evaporating Heating Bending

Dissolving

Chemical changes: No!Burning Rotting Decomposing

DefinitionsMatter: Stuff. You're made of it. So is a desk.

DefinitionsLet's smash it up and zoom in about 100,000 times

DefinitionsThis is a cell. You're in the wrong class.

Well, maybe not....it's a mixture. Specifically a heterogeneous mixture (each little bit is not exactly identical to the next).

Compare this to a homogeneous mixture like gatorade.

Mixture: multiple substances combined physically. They may be separated without any chemical reactions.

DefinitionsSo I do lots of smashing up, filtering, extracting, and separating until I have pure substances in each flask:

At this point, these things cannot be physically separated anymore

DefinitionsNow I start trying to break these down chemically.

If it can't be broken down into anything else, it's an element: a pure substance not made of any other substances

If it can be split apart chemically into other substances, it's a compound: a combination of elements chemically combined together in a fixed ratio.

DefinitionsNow I take my element, and I start physically smashing it up again

When it gets as small as it can get, I have an atom: the smallest piece of an element that has all the chemical properties of that element.

C

If I physically chop up compounds into the smallest part that has the properties of the compound, I'll get

one of two things:

On the left is a compound that has molecules: more than one atom bonded together into a group.

On the right is a compound with no molecules—every sodium and chlorine is just jammed next to each other in some pattern. Instead, it has formula units: the ratio of the two elements.

How do you know which you have? We'll get to that later.

Key Words Mixture

Heterogeneous Homogeneous

Compound Element

Atom

Molecule

Fomula Unit

As a flow chartMixture

Heterogeneous or Homogeneous

Compounds

ElementsAtoms

Molecules/Formula Units

Physical Separation

Chemical Separation

An Example (only carbon dioxide done completely for visual simplicity)

Air, Homogeneous (nitrogen, oxygen,

argon, carbon dioxide)

Carbon dioxide

Carbon, oxygen

C

CO2

O

nitrogen

oxygen

argon

Phases of MatterSolid: molecules/atoms are fixed in place, have little energy, and stick together well.

Liquid: molecules/atoms are free to move around, have a moderate amount of energy, but still generally stick together.

Gas: molecules/atoms whizz around like crazy, have oodles of energy, and generally don't stick together at all. The only real difference between liquid and gas is density/energy.

Plasma: atoms have been stripped of all electrons at absurd energies/temperatures. Not relevant to most of life.

(Aqueous): not really a phase, but important enough to be a pretend one. Just means your compound/element is dissolved in water.

Let's Get This Out of the Way Now

What is the temperature of ice?

Let's Get This Out of the Way Now

What is the temperature of ice?

NOT 0oC (32oC).

This is the melting point—the maximum temperature at which you can have ice (or minimum at which you can have water). Any given chunk of ice may very well be much colder.

(the same idea applies to steam)