Antonio Padilla
AP Chemistry Chapter 2 Review: Atoms, Molecules, and Ions
I.
2.1 The Atomic Theory of Matter
Dalton’s Atomic Theory
1.
Each element is composed of extremely small particles called atoms.
2.
All atoms of a given element are identical, but the atoms of one element are different from the atoms of all other elements.
3.
Atoms of one element are identical, but the atoms of one element are different element by chemical reactions; atoms are neither created nor destroyed in chemical reactions.
4.
Compounds are formed when atoms of more than one element combine; a given compound always has the same relative number and kind of atoms.
 Law of constant composition – in each compound, the relative numbers and kinds of atoms are constant.
 Law of conservation of mass – the total mass of materials present after a chemical reaction is the same as the total mass present before the reaction
 Law of multiple proportions – If two elements A and B combine to form more than one compound, the masses of B that can combine with a given mass of A are in the ratio of small whole numbers
II.
2.2 The Discovery of Atomic Structure
 Subatomic particles – particles that make the complex structure of an atom
The Electron (Cathode Rays)
 Cathode rays – radiation that originated at the negative electrode and traveled to the positive electrode
 J.J. Thomson observed that cathode rays are the same regardless of the identity of the cathode material. He later described the cathode rays as streams of negatively charged particles that we now call electrons.

Thomson measured the charge/mass ratio of the electron to be 1.76 x 10 8 coulombs/gram (C/g).
Millikan Oil-Drop Experiment (Electrons)
Streams of negatively charged particles were found to emanate from cathode tubes, causing fluorescence.

Once the charge/mass ratio of the electron was known, determination of either the charge or the mass of an electron would yield the other.
Robert Millikan determined the charge on the electron in 1909.
Radioactivity
 Spontaneous emission of high-energy radiation by an atom
 First observed by Henri Becquerel and studied by Marie and Pierre Curie
 Its discovery showed that the atom had more subatomic particles and energy associated with it.
Three types of radiation: a) a particle (positively charged) b) b particles (negatively charged, like electrons) c) y rays (uncharged)
The Atom
 “Plum pudding” model theory put forward by J.J. Thomaon
 Positive sphere of matter with negative electrons embedded in it.

Discovery of the Nucleus
 Ernest Rutherford shot a particles at a thin sheet of foil and observed the pattern of scatter of the particles
 Since some particles were deflected at large atoms, Thomson’s model could not be correct which led to the nuclear view of the atom.
 Rutherford postulated a very small, dense positive center with the electrons around the outside
 Most of the atom is space
 Also lead to the discovery of the other subatomic particles like protons and neutrons.

III.
2.3 The Modern View of Atomic Structure
 Protons and neutrons are found in the nucleus; electrons travel around the nucleus.
5.486 times 10 to the negative fourth
Atomic Number
Isotopes
 Atoms of the same element with different masses
 Different number of neutrons but the same number of protons
IV.
Atomic Weights
Atomic Mass Unit
 1 amu = 1.66054 x 10 -24 g

Atomic Weight
 Average mass is found using all isotopes of an element weighted by their relative abundances. This is an element’s atomic weight.
 Atomic weight = ∑ [(isotope mass) x (fractional natural abundance)] for ALL isotopes
V.
2.5 The Periodic Table
 Rows on the periodic table are called periods
 Columns are called groups
 Elements in the same group have similar chemical properties
Metals
 Shiny luster
 Conducting heat and electricity
 Solids except mercury
Nonmetals
 They can be solid (like carbon), liquid (like bromine), or gas (like neon) at room temperature
Metalloids
 Properties are sometimes like metals and sometimes like nonmetals

VI.
2.6 Molecules and Molecular Compounds
 Molecular compounds – composed of molecules and almost always contain only nonmetals
 Diatomic molecules – elements that occur naturally as molecules containing two atoms
 I Bring Clay For Our New Home
Types of Formulas
 Empirical formulas – the lowest whole-number ratio of atoms of each element in a compound
 Molecular formulas – the exact number of atoms of each element in a compound
 Structural formulas – show the order in which atoms are attached. They do not depict the three-dimensional shape of molecules
 Perspective drawings, ball-and-stick models, and space-filling models show the three-dimensional order of the atoms in a compound.
VII.
2.7 Ions and Ionic Compounds
 When an atom of a group of atoms loses or gains electrons, it becomes an ion
 Cations are formed when at least one electron is lost. Monatomic cations are formed by metals.
 Anions are formed when at least one electron is gained. Monatomic anions are formed by nonmetals, except the noble gases.
 Polyatomic ions – when a group of atoms will gain or lose electrons
Polyatomic cation:
Ammonium ≡ NH
4
+
Polyatomic anion:
Sulfate ≡ SO
4
2−
 Ionic Compounds – generally formed between metals and nonmetals

 Electrons are transferred from the metal to the nonmetal. The oppositely charged ions attract each other. Only empirical formulas are written.
VIII.
Naming Inorganic Compounds
