AP Chemistry

1.     Basic Atomic Structure (Atoms and Ions)        (Subatomic Particles)  Subatomic Particle          Mass        Charge         Proton                 ~ 1 a.m.u           +1        Electron               ~ 0 a.m.u.           -1        Neutron               ~ 1 a.m.u.            0    a.m.u. = atomic mass unit = 1/12 the mass of a carbon-12 atom

Basic Atomic Structure (Atoms and Ions)

2.    Basic Atomic Structure Number of Protons = ElementThe number of protons in an atom or ion determines what element it is.For example, if a particle has 6 protons in it, it must be carbon.

3.     Basic Atomic Structure - Atomic NumberThe atomic number of an atom or an ion is equal to its number of protons.Atomic Number = Number of ProtonsExample:If you look up potassium (K) in the periodic table, it has an atomic number of 19, meaning that all potassium atoms and all potassium ions contain 19 protons.

4.   Atomic Mass NumberThe Atomic Mass of Number of an atom or an ion is equal to the sum of its number of protons plus its number of neutrons Atomic Mass Number = (# of Protons) + (# of Neutrons)Example:A particle with 6 protons and an atomic mass number of 14 has 8 neutrons.

 5.    Particle Names A particle’s name will sometimes include the atomic mass number of the particle.For example, chlorine-37 is a chlorine atom that has an atomic mass number of 37, meaning that it has a total of 37 protons and neutrons in its nucleus.Since the atomic number for chlorine is 17, any chlorine atom or ion always has 17 protons.  Therefore, a chlorine-37 atom has 20 neutrons, because 37 minus 17 equals 20.

6.     Ions = Charged Particles  Ions are formed when atoms gain or lose electrons. Positive ions (cations) are formed when a neutral atom loses electrons. Negative ions (anions) are formed when a neutral atom gains electrons. Metallic atoms tend to lose electrons to form positive ions (also known as cations). Nonmetallic atoms tend to gain electrons to form negative ions (a.k.a. anions).

7.     ChargeThe charge on an atom or an ion is equal to its number of protons minus its number of neutrons.Charge = (# of Protons) - (# of Electrons)Example:A particle with 34 protons and 36 electrons has a charge of -2.

9.     Isotopes  Isotopes are atoms of the same element that have a different number of neutrons.  Therefore, isotopes have the following characteristics: Isotopes have the same atomic number (same number of protons), but a different atomic mass number (a different number of neutrons). Isotopes behave the same chemically, because they are the same element.  The only difference is that one is heavier than the other, because of the additional neutrons. For example, carbon-12 and carbon-14 are both isotopes of carbon.  Carbon-12 has 6 neutrons; carbon-14 has 8 neutrons.

 10.     Atomic Weight The atomic weight of an element (as it appears in the periodic table) is the weighted average of the atomic mass numbers of all of the isotopes for that element.  For example, the atomic weight of carbon (as shown on the periodic table) is 12.011 a.m.u. (atomic mass units).  However, there is no one carbon atom that has a mass of 12.011 a.m.u.  Carbon exists as four different isotopes:  carbon-11, carbon-12, carbon-13, and carbon-14, which have approximate atomic mass numbers of 11, 12, 13, and 14 a.m.u., respectively.  If you know the percent abundance of each of those isotopes, you can calculate the atomic weight of carbon by determining the weighted average of the atomic mass numbers of the four isotopes.  That weighted average comes to 12.011 a.m.u. The reason that the atomic weight is closer to 12 than it is to the other atomic mass numbers is that carbon-12 is the most common isotope of carbon.For most elements, the atomic mass number of the most common isotope for that element can be determined by rounding the atomic weight for that element to the nearest whole number.  For example, the atomic weight of aluminum is 26.98154 a.m.u.   Therefore, the most common isotope for aluminum can be assumed to be aluminum-27.

8.    Atomic WeightThe atomic weight of an element (as it appears in the periodic table) is the weighted average of the atomic mass numbers of all of the isotopes for that element.  For example, the atomic weight of carbon (as shown on the periodic table) is 12.011 a.m.u. (atomic mass units).  However, there is no one carbon atom that has a mass of 12.011 a.m.u.  Carbon exists as four different isotopes:  carbon-11, carbon-12, carbon-13, and carbon-14, which have approximate atomic mass numbers of 11, 12, 13, and 14 a.m.u., respectively.  If you know the percent abundance of each of those isotopes, you can calculate the atomic weight of carbon by determining the weighted average of the atomic mass numbers of the four isotopes.  That weighted average comes to 12.011 a.m.u. The reason that the atomic weight is closer to 12 than it is to the other atomic mass numbers is that carbon-12 is the most common isotope of carbon.For most elements, the atomic mass number of the most common isotope for that element can be determined by rounding the atomic weight for that element to the nearest whole number.  For example, the atomic weight of aluminum is 26.98154 a.m.u.   Therefore, the most common isotope for aluminum can be assumed to be aluminum-27.

 1.    Binary Ionic Compounds Binary Ionic Compounds (compounds consisting of two different ions)Binary ionic compounds are formed between a metal and a nonmetal.  Metallic elements tend to lose electrons (forming positive ions) in order to become isoelectronic with (to have the same number of electrons as) a noble gas.  Nonmetals tend to gain electrons (forming negative ions) to become isoelectronic with a noble gas.  The charge on an ion is also referred to as the oxidation number of that element when it is in that ionic form.1.The oxidation number of the nonmetallic element in a binary ionic compound is always equal to the number of electrons that it needs to gain to become isoelectronic with a noble gas.  For example, an oxygen atom needs 2 electrons to become isoelectronic with neon, so an oxide ion always has a charge of -2.  A nitride ion always has a charge of -3.  Chloride is always -1.2.The oxidation number for metals is not always as simple.  Some metals are monovalent, meaning that they tend to form only one type of ion.  For example, the oxidation number of alkali metals (Li, Na, K, etc.) is always +1 in a compound.  The oxidation number of alkaline earth metals (Be, Mg, Ca, etc.) is always +2 in a compound.  Silver ions always have a +1 charge.  Zinc ions always have a +2 charge.  Aluminum ions always have a +3 charge.3.Most other metals can have more than one oxidation number in a compound.  There are 5 metals, in particular, that usually have one of two different oxidation numbers when they are part of a compound.  These are bivalent metals:Bivalent Metal     Oxidation Numbers   Cu+1 or +2      Hg+1 or +2   Fe+2 or +3   Sn+2 or +4   Pb+2 or +4

2.    The Stock SystemThe stock system of nomenclature is used for naming compunds that contain a multivalent metal (a metal that can form more than one type of ion). In this system, the oxidation number (the charge on the ion) of the metal is shown in the parentheses using Roman numerals.Example: iron oxide would be an ambiguous name for the compound FeO, because iron and oxygen can also form FE202. Calling either of these compounds iron oxide would not indicate which compound you were referring to. In the compound FeO, the oxide ion has a charge of -2, so the iron must have a charge of +2.

Basic Atomic Structure (Atoms and Ions)

Chemical Nomenclature