MATTER

STRUCTURE OF MATTER According to the modern atomic model, protons and neutrons are found in the nucleus, and electrons are found outside the nucleus in a region called the electron cloud. Protons have a positive charge. Electrons have a negative charge. Neutrons are neutral, they have no charge.

Protons and Neutrons are made up of smaller particles called quarks. There is an up quark and a down quark held together by particles called gluons. Protons have more up quarks than down quarks. Neutrons have more down quarks than up quarks.

ELECTRON ENERGY LEVELS The first energy level, closest to the nucleus, can hold only 2 electrons (e-). The second energy level can hold only 8 e-. The third energy level is stable when it has 8 e-. (can actually hold 18 in all, but only after the fourth energy level has at least 2)

ISOTOPES Two or more atoms that have the same number of protons but different numbers of neutrons are called isotopes. If they have the same # of protons, they have the same atomic #, which means they are all the same element. If they have different numbers of neutrons, they have different mass numbers.

HYDROGEN ISOTOPES Atomic # = Mass # =

IONS Charged atoms (or groups of atoms) are called ions. An atom becomes charged by either gaining or losing one or more electrons. An atom that has lost one or more e- is a positive ion (cation). The atom now has more protons than e-. An atom that has gained one or more e- is a negative ion (anion). The atom now has more e- than protons.

cation

0 -1 anion

+1 +1 cation -1 anion The oppositely charged ions will now attract each other and make an ionic chemical bond. This forms sodium fluoride…the stuff in your toothpaste that kills bacteria.

Generally, atoms do not gain or lose protons. An atom will become an ion only by gaining or losing e-. The number of protons (or neutrons) will only change during nuclear fission, nuclear fusion, or radioactive decay. What charge will an atom have if it loses 3 e-? What charge will an atom have if it gains 2 e-?

The smallest unit of any substance (example: water) that still retains the properties of the substance is a molecule. A molecule is any two or more atoms combined by sharing electrons. (non-metals only, even two of the same element) A compound is any two or more different elements combined. Chemical reactions involve rearrangement of atoms, not the destruction or creation of them.

a representation of one molecule of a substance by showing the symbol of each element in the substance and the number of each element in the molecule Example: H 2 O is the formula for water because it represents one molecule of water. If you broke the substance down any farther, it would not be water.

If you have a formula like C 7 H 5 (NO 2 ) 3, you would have 7 carbon atoms, 5 hydrogen atoms, 3 nitrogen atoms, and 6 oxygen atoms. Any time you have atoms inside a parenthesis ( ) with a subscript number after the ( ), you multiply the number after the ( ) by the number of each element inside the ( ) to obtain the total number of atoms for each element inside the ( ).

The group of atoms inside the ( ) is called a polyatomic ion. more than one atom has a charge

1 s 2 2 s 2 p 6 3 s 2 p 6 d 10 4 s 2 p 6 d 10 f 14 5 s 2 p 6 d 10 f 14 6 s 2 p 6 d 10 7 s 2 p 6 Energy level orbital Maximum # of e- the orbital can contain