An element is one kind of atom (a certain number of protons per atom).

A compound is two or more different elements bonded together.

A mixture contains different elements or compounds mixed but not bonded to each other. For example, air is a mixture of gases: 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, and small amounts of other gases.

YouTube video about elements, compounds and mixtures here.

Elements and compounds are written as species using chemical notation, with subscript used for the number of each element bonded in the species, and superscript used for the charge on the species.

In chemical equations, reactants are written on the left and products on the right, with an arrow in the middle meaning "becomes".

In a balanced equation, each species has a coefficient to show relatively how much of each is required or produced in the reaction.

Balancing practice here.

PowerPoint 2007 presentation on chemical notation here.

All matter is made of tiny vibrating particles (millions of times smaller than the smallest speck we can see without a microscope) and a lot of empty space.

Chemical reactions occur because particles are colliding under the right conditions.

Web page on the scale of small things here.

The carbon atom shown there shows the atomic radius (the electron cloud) and is about 10000 times the size of the nucleus by itself.

In chemical equations, the state of each species can be represented by a symbol in subscript and brackets: (s) solid, (l) liquid, (g) gas, and (aq) aqueous solution (dissolved in water).

In a solid, the particles are moving relatively slowly and are fixed in place.

In a liquid, the particles are moving faster and will change shape to fit in a container.

In a gas, the particles are far apart, moving very quickly, and will spread out to fill any container.

YouTube video about solid, liquid and gas here.

Temperature and heat are related but they are not the same thing.

Heat is energy transferred from one substance to another, measured in J (joules).

Temperature is a measurement of the movement of particles, measured in °C (degrees Celsius).

YouTube video about temperature and heat here.

Primary forces (bonds) are the attraction between atoms: ionic (metal to non-metal), metallic (metal to metal), and covalent (non-metal to non-metal).

Flash animation about metallic bonding here.

Ionic compounds molten or in solution can also conduct electricity, but the ions flow to carry the charge not electrons like in a metal.

All three kinds of primary bonding can form network (lattice) structures, but covalent bonding can also form molecules. If the two atoms in a covalent bond have different electronegativity (attraction for electrons), the bond will be polar; it will have partially positive and negative ends.

If polar bonds in a molecule don't cancel out (that is, they share a direction) the molecule will be polar.

Secondary forces (interactions) are the attraction between molecules and are much weaker than primary forces.

In order from weakest to strongest, the secondary interactions are: dispersion forces (between non-polar molecules), dipole-dipole forces (between polar molecules), and hydrogen bonding (between polar molecules with N-H, O-H or F-H bonds).

YouTube video about electronegativity and polar bonds here.

Bonding properties practice here.

In molecules, regions of high negative charge (such as bonding or non-bonding valence electron pairs) will repel each other to form a shape where, in 3D, these regions are far away from each other but still the same distance from the central atom.

Molecular shapes often influence whether or not the molecule will be polar, since the shape will determine whether dipole directions share a direction or cancel out.

YouTube video about shapes of molecules here.

Practice drawing small molecules here.