AP Chemistry/The Basics

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You should remember everything here from your high-school level chemistry class.

Contents 1 Units and Measurement 1.1 Significant Figures 1.1.1 Measured vs. Exact Numbers 1.2 The Mole and Avogadro's Number 1.3 Multiplying and Significant Figures 1.4 Adding and Significant Figures 2 States of Matter 3 History of Chemistry 4 Modern Atomic Theory 5 Electrons 5.1 Filling Electron Shells 5.2 Writing Electron Configurations 6 VSEPR Theory 7 Hybrid Orbitals 8 Sigma and Pi Bonds 9 Resonance 10 The Periodic Table 11 The Quantum Numbers 11.1 Principal Quantum Number 11.2 Angular Momentum Quantum Number 11.3 Magnetic Quantum Number 11.4 Spin Quantum Number 12 Oxidation Numbers 13 Naming Compounds 13.1 Binary Compounds 13.2 Binary Acids 13.3 Ternary Compounds 13.4 Ternary Acids 13.5 Stock System

[edit] Units and Measurement

• Fahrenheit is not used on the AP exam. Celsius (°C) and Kelvin (K) are used. Pure water freezes at 0° Celsius (273K) and boils at 100°C (373K).

[edit] Significant Figures

• Digits 1 through 9 are significant, and so are zeroes in between them. For example, the number 209 has three significant figures.
• Zeroes to the right of all other digits are only significant if there is a decimal point written. 290 has 2 sig figs, 290. has three, and 290.0 has four.

[edit] Measured vs. Exact Numbers

Exact numbers can be counted, like a dozen. Measured numbers are approximate, such as 12 grams.

[edit] The Mole and Avogadro's Number

12 grams of Carbon-12 contain exactly one mole (6.02 * 10^23) of molecules. This is a measured number known as Avogaro's number. It is easy to convert between atomic mass, grams, and particles using Avogadro's number. If you don't know how, you really shouldn't be taking the AP test.

[edit] Multiplying and Significant Figures

Multiplying measured numbers in Chemistry is not like multiplying in math. 5 * 92 equals 460 in math class, but it equals 500 in chemistry. This is because the 5 only has one significant figure, so the answer has to be rounded to one sig fig. If 5.0 and 92 were multiplied, on the other hand, the answer would be 460 in both subjects.

[edit] Adding and Significant Figures

1. First, align all the numbers vertically, as if you were going to add them. DO NOT WRITE IN EXTRA ZEROS AS PLACEHOLDERS.
2. Add
3. Round to the smallest place that contains a digit in every number.

Example: 210 + 370. + 539

  21
  370.
  539
+----
 1119 ≈ 1120

[edit] States of Matter

• Solid (s) - definite shape and volume. Vibrates in place, but does not flow.
• Fluids - take the shape of their container.
  • Liquid (l) - definite volume
  • Gas (g) - variable volume (compressible)

[edit] History of Chemistry

• Democritus - philosopher who made the idea of atoms.
• Antoine Lavoisier - discovered Law of Conservation of Mass, which states that mass does not appear or disappear in chemical reactions, only rearrange.
• John Dalton - first scientist to scientifically describe atomic theory.
  1. Matter is made from indestructible particles called atoms.
  2. Atoms of the same element are the same.
  3. Compounds are two or more atoms bonded together.
  4. Chemical reactions are the rearrangement of atoms.
• J.J. Thomson - discovers the electron.
• Robert Millikan - discovers the mass and charge of electrons.
  • "Raisin Pudding model" - atoms are like pudding, with electrons as raisins.
• Ernest Rutherford - through his gold foil experiment, discovers the nucleus. Since most of the alpha particles he shot through the gold were not deflected, he concluded that most of an atom is empty space.

[edit] Modern Atomic Theory

Atoms are made up of protons, neutrons, and electrons. Protons and neutrons weigh approximately 1 AMU, and electrons have a negligible mass. Elements are determined by the number of protons in the atom, known as the atomic number. The number of neutrons varies, creating different isotopes of different mass. The atomic mass of an atom is the sum of its protons and neutrons, both of which are found in the nucleus.

[edit] Electrons

Electrons are arranged into shells that surround the atom. Each shell has 1-4 subshells, which themselves have 1-7 orbitals, each of which holds two electrons.

Shell	Subshell	Orbitals
1	s	1
2	s, p	1 + 3 = 4
3	s, p, d	1 + 3 + 5 = 9
4	s, p, d, f	1 + 3 + 5 + 7 = 16

[edit] Filling Electron Shells

• Aufbau principle - fill the lowest energy subshells first, in accordance with the following image:

• Hund's rule - fill each orbital in a subshell with one electron before putting a second electron in any of those orbitals.

[edit] Writing Electron Configurations

E.g. sodium = 1s²2s²2p⁶3s¹

[edit] VSEPR Theory

Electrons in a compound will try to move as far apart from each other as possible. Bonded pairs repel more strongly than unbonded pairs.

[edit] Hybrid Orbitals

The moving apart of electron pairs requires the hybridization of orbitals. These hybrids range from sp to sp³d², having two to six pairs.

[edit] Sigma and Pi Bonds

• Sigma bond - forms in all compounds
• Pi bonds - one or more are formed per extra electron pair that is shared among two atoms. These bonds are weaker than sigma bonds.

[edit] Resonance

Sometimes, there is more than one "correct" way to draw a substance. In reality, the structure of the substance is an average of the drawn variations.

[edit] The Periodic Table

You should already be familiar with this. Each row is called a period, and each column is a group or family. Nonmetals and metals are separated by a jagged line on the right side. (Hydrogen is also a non-metal). Elements that border the line are called metalloids, and share characteristics with both metals and nonmetals.

[edit] The Quantum Numbers

These four numbers are used to describe the location of an electron in an atom.

Number	Symbol	Possible Values
Principal Quantum Number	n	1, 2, 3, 4 ...
Angular Momentum Quantum Number	l	0, 1, 2, 3 ... (n - 1)
Magnetic Quantum Number	ml	-(n - 1) ... -1, 0, +1 ... +(n - 1)
Spin Quantum Number	ms	+½, -½

[edit] Principal Quantum Number

Determines the shell the electron is in. Main component in determining the energy of the electron (higher n corresponds to higher energy), as well as nuclear distance (higher n means further from the nucleus).

[edit] Angular Momentum Quantum Number

Determines the subshell the electron is in. These correspond to the s, p, d, f shells (0 corresponds to s, 1 to p, 2 to d etc.).

Image:1s orbital.jpg
S orbital	P orbitals (3)	D orbitals (5)

[edit] Magnetic Quantum Number

Determines the orbital in which the electron lies. E.g. there are three p orbitals in shell 2; the magnetic quantum number determines which one of these electron resides in. The different orbitals are oriented at different angles around the nucleus.

[edit] Spin Quantum Number

Determines whether, for example, an electron in an s shell is moving clockwise or counterclockwise from a specific viewing angle.

[edit] Oxidation Numbers

Oxidation numbers are a way of keeping track of electrons and making sure that components of a compound match by the correct ratios.

• Pure elements have an oxidation number of zero.
• Ions, monoatomic or polyatomic, have the same charge and oxidation number.
• Covalent and ionic compounds have an oxidation number of zero.
• Bonded Group 1 metals are +1, Group 2 are +2, and halogens are -1, unless bonded with oxygen.
• Bonded oxygen is -2 unless it is in a peroxide (OH), where it is -1, or with fluorine, where it is positive.
• Bonded hydrogen is ±1, depending on if it is bonded with a metal (-1) or nonmetal (+1).

[edit] Naming Compounds

[edit] Binary Compounds

(First element's name) (Second element's name + ide) e.g. Sodium Chloride.

[edit] Binary Acids

Hydro(nonmetal)ic acid. E.g. Hydrobromic acid (HBr)

[edit] Ternary Compounds

(First element's name) (polyatomic ion's name) e.g. Sodium Hydroxide (NaOH). Note that there is an exception - the ammonium ion (NH₄⁺) can replace the first element.

[edit] Ternary Acids

Ternary acids contain hydrogen, a nonmetal, and oxygen (in that order). If the ion ends in -ate, the acid will be (nonmetal)ic acid. If the ion is -ite, the acid is named (nonmetal)ous acid.

[edit] Stock System

Some elements, especially transition metals, can have many oxidation numbers. As a result, the positive oxidation number has to be written in, using Roman numerals. For example, N₂O₃ is Nitrogen (III) oxide and NO₂ is Nitrogen (IV) oxide.