Atomic Structure, Periodic Table, and Chemical Nomenclature: General Chemistry Study Notes

The Modern View of Atomic Structure

Subatomic Particles

Atoms are composed of three fundamental subatomic particles: protons, neutrons, and electrons. Protons and neutrons reside in the nucleus, which is extremely small compared to the overall atom. Electrons are found outside the nucleus.

• Proton (p+): Positive charge (+1), mass ≈ 1.0073 amu

• Neutron (n0): No charge, mass ≈ 1.0087 amu

• Electron (e-): Negative charge (-1), mass ≈ 0.00055 amu (very small, often ignored in mass calculations)

Particle	Charge	Mass (amu)
Proton	+1	1.0073
Neutron	0	1.0087
Electron	-1	0.00055

Atomic number (Z): Number of protons in the nucleus. Mass number (A): Total number of protons and neutrons in the nucleus. Isotopes: Atoms with the same Z but different A.

$A = Z + N$

Atomic Mass Unit (amu)

The atomic mass unit is defined as:

$1~ ext{amu} = 1.66054 imes 10^{-24}~ ext{g}$

Atomic masses are extremely small, so amu is used for convenience.

Average Atomic Mass (Atomic Weight)

The average atomic mass (or atomic weight) of an element is calculated from the masses of its isotopes weighted by their relative abundances.

$ext{Average atomic mass} = rac{ ext{Sum of (isotopic mass} imes ext{fractional abundance)}}{ ext{Total abundance}}$

The Periodic Table

Organization and Groups

The periodic table arranges elements by increasing atomic number (Z). Rows are called periods, columns are groups or families. Elements in the same group have similar chemical properties.

Group	Name	Elements
1A	Alkali metals	Li, Na, K, Rb, Cs, Fr
2A	Alkaline earth metals	Be, Mg, Ca, Sr, Ba, Ra
6A	Chalcogens	O, S, Se, Te, Po
7A	Halogens	F, Cl, Br, I, At
8A	Noble gases	He, Ne, Ar, Kr, Xe, Rn

• Metals: Left side and majority of the table

• Nonmetals: Right and top side (except H)

• Metalloids: Border the stair-step line, have properties intermediate between metals and nonmetals

Molecules and Compounds

Molecules

A molecule consists of two or more atoms bound tightly together. The chemical formula indicates which atoms are present and their proportions.

• Diatomic molecules: Made of two atoms (e.g., H2, N2, O2, F2, Cl2, Br2, I2)

• Molecular compounds: Composed of different atoms (e.g., CH4, CO, H2O, HCl, H2SO4)

Types of Formulas

• Molecular formula: Exact number of atoms of each element in a compound

• Empirical formula: Lowest whole-number ratio of atoms in a molecule

Molecular Formula	Empirical Formula
C2H4	CH2
H2O2	HO
C6H6	CH

Structural Formulas and Models

• Structural formulas: Show the order in which atoms are bonded

• Perspective drawings: Use wedges and dashed lines for 3D shape

• Ball-and-stick models: Atoms as spheres, bonds as sticks

• Space-filling models: Show scaled-up atoms

Ions and Ionic Compounds

Ions

• Cations: Positively charged ions (loss of electrons)

• Anions: Negatively charged ions (gain of electrons)

For a neutral atom: $p^+ = e^-$

Predicting Ionic Charges

• Group 1A: +1 ions

• Group 2A: +2 ions

• Group 7A (halogens): -1 ions

• Group 6A: -2 ions

Ionic Compounds

• Formed by transfer of electrons between metals and nonmetals

• Arranged in 3D ionic lattices

• Electrically neutral: total positive charge equals total negative charge

Formula of Ionic Compounds

• Charge on cation becomes subscript on anion and vice versa

• If subscripts are not in lowest ratio, divide by greatest common factor

Naming Compounds

Cations

• Named after the metal (e.g., Na+ = sodium ion)

• Transition metals may have variable charge, indicated by Roman numerals (e.g., Fe2+ = iron(II) ion)

Anions

• Monatomic anions: add -ide (e.g., Cl- = chloride ion)

• Polyatomic anions: may use -ide, -ate, -ite, or prefixes (e.g., NO3- = nitrate, SO42- = sulfate)

Charge	Formula	Name
1+	Na+	sodium ion
2+	Mg2+	magnesium ion
1-	Cl-	chloride ion
2-	SO42-	sulfate ion

Common Polyatomic Anions

Charge	Formula	Name
1-	OH-	hydroxide ion
1-	NO3-	nitrate ion
2-	CO32-	carbonate ion
2-	SO42-	sulfate ion
3-	PO43-	phosphate ion

Naming Ionic Compounds

• Name the cation first, then the anion (e.g., NaCl = sodium chloride)

Acid Nomenclature

• If the anion ends in -ide, change to -ic acid and add prefix hydro- (e.g., Cl- = hydrochloric acid)

• If the anion ends in -ite, change to -ous acid (e.g., SO32- = sulfurous acid)

• If the anion ends in -ate, change to -ic acid (e.g., SO42- = sulfuric acid)

Names and Formulas of Binary Molecular Compounds

• Binary molecular compounds have two nonmetal elements

• Element farthest left on the periodic table is written first

• Prefixes denote the number of atoms (mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-)

• Second element ends in -ide

Prefix	Meaning
mono-	1
di-	2
tri-	3
tetra-	4
penta-	5
hexa-	6
hepta-	7
octa-	8
nona-	9
deca-	10

Nomenclature of Organic Compounds

• Organic compounds contain carbon and hydrogen, often with other elements

• Hydrocarbons: only carbon and hydrogen

• Alkanes: simplest hydrocarbons, end in -ane (e.g., methane, ethane, propane, butane)

• Functional groups: replace hydrogen atoms, create new classes of organic compounds

• Alcohols: replace hydrogen with -OH group, names end in -ol (e.g., methanol, ethanol)

Examples and Applications

• Calculate numbers of protons, neutrons, and electrons for isotopes

• Determine empirical and molecular formulas

• Predict ionic charges based on group number

• Name and write formulas for ionic and molecular compounds

• Apply acid nomenclature rules

Additional info: These notes cover foundational topics from Ch.2 (Atoms, Molecules, and Ions) and Ch.3 (Chemical Reactions and Reaction Stoichiometry), with context from Ch.1 (Matter, Energy, and Measurement) and Ch.4 (Reactions in Aqueous Solution) as relevant to nomenclature and periodic table organization.