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 and dense, while electrons are located outside the nucleus.

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

• Neutron (n0): No charge (0), mass ≈ 1.0087 amu

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

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

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.

• Example: 12C (carbon-12), 13C (carbon-13), 137Cs (cesium-137)

Atomic mass unit (amu): 1 amu = 1.66054 × 10-24 g

Calculating Subatomic Particles in Isotopes

Example Table

Isotope	p+	n0	e-
Hydrogen-1	1	0	1
Hydrogen-2	1	1	1
Oxygen-16	8	8	8
Bromine-81	35	46	35

To find the number of neutrons: $n^0 = A - Z$

Atomic Mass and Atomic Weight

Definition and Calculation

Atomic mass units (amu) are used for extremely small masses of atoms. The average atomic mass (atomic weight, AW) is calculated from the masses and relative abundances of isotopes.

• Example: Carbon has two main isotopes, 12C and 13C.

Isotope	Isotopic mass (amu)	Abundance (%)	Fractional abundance
12C	12.00000	98.93	0.9893
13C	13.00335	1.07	0.0107

Average atomic mass formula: $\text{Avg. atomic mass} = (M_1 \times f_1) + (M_2 \times f_2) + \ldots$ where $M$ is isotopic mass and $f$ is fractional 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 are on the left side; most elements are metals.

• Nonmetals are on the right/top (except H).

• Metalloids border the stair-step line and have properties of both metals and nonmetals.

Molecules and Chemical Formulas

Types of Molecules

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

• Diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2

• Molecular compounds: Contain at least two types of atoms (e.g., CH4, CO, H2O, HCl, H2SO4)

Types of Chemical Formulas

Molecular, Empirical, and Structural Formulas

• Molecular formula: Shows the exact number of atoms of each element (e.g., C2H6).

• Empirical formula: Shows the simplest whole-number ratio (e.g., CH3).

Molecular Formula	Empirical Formula
C2H6	CH3
H2O2	HO
C6H6	CH

• Structural formula: Shows the order in which atoms are bonded.

• Perspective drawings: Use wedges/dashes for 3D shape.

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

• Space-filling models: Show scaled-up atom sizes.

Ions and Ionic Compounds

Formation and Types

• If electrons are added or removed from a neutral atom, an ion forms.

• Cations: Positively charged (loss of electrons), e.g., Na+

• Anions: Negatively charged (gain of electrons), e.g., Cl-

Many atoms gain/lose electrons to achieve the same number as the nearest noble gas.

• Group 1A: +1 ions

• Group 2A: +2 ions

• Group 7A: -1 ions

• Group 6A: -2 ions

Ionic Compounds

Properties and Formulas

• Ionic compounds are formed between metals and nonmetals.

• They are electrically neutral: total positive charge equals total negative charge.

• Example: NaCl (table salt) consists of Na+ and Cl- ions.

To write the formula, balance the charges so the compound is neutral.

Ions	Formula
Al3+ + Cl-	AlCl3
Na+ + PO43-	Na3PO4

Molecular Compounds

Properties

• Composed of nonmetals only (e.g., H2O, CH4, SO2).

• Electrons are shared between atoms.

Compound	Type
NaCl	Ionic
CaCl2	Ionic
NH4Br	Ionic
C2H5SH	Molecular

Naming Compounds

Cations and Anions

• Cations from metals: same name as the metal (e.g., Na+ = sodium ion).

• Transition metals: use Roman numerals for charge (e.g., Fe2+ = iron(II) ion).

• Anions: add -ide to the root (e.g., Cl- = chloride ion).

• Polyatomic anions: use -ate, -ite, or other endings (e.g., NO3- = nitrate ion).

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

Monatomic and Polyatomic Anions

Naming Rules

• Monatomic anions: add -ide (e.g., F- = fluoride ion).

• Polyatomic anions: use -ate, -ite, or prefixes (e.g., ClO4- = perchlorate ion).

• Additional hydrogens: add hydrogen or dihydrogen (e.g., HCO3- = hydrogen carbonate).

Charge	Formula	Name
1-	OH-	hydroxide ion
CO32-	carbonate ion
PO43-	phosphate ion

Naming Ionic Compounds

• Name the cation first, then the anion (e.g., CaCl2 = calcium chloride).

Compound	Name
CaCl2	calcium chloride
Na2SO4	sodium sulfate

Acid Nomenclature

• If the anion ends in -ide, change to -ic acid and add 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., NO3- = nitric acid).

Anion	Name	Acid
Cl-	chloride	hydrochloric acid
SO42-	sulfate	sulfuric acid
NO2-	nitrite	nitrous acid

Binary Molecular Compounds

Naming Rules

• Contain two nonmetals.

• Element farther left on the periodic table is written first.

• Prefixes indicate the number of atoms (mono-, di-, tri-, tetra-, etc.).

• 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

• Example: CO2 = carbon dioxide, N2O4 = dinitrogen tetroxide

Nomenclature of Organic Compounds

Hydrocarbons and Functional Groups

• 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).

• Alcohols: Replace a hydrogen atom with an -OH group; names end in -ol (e.g., methanol, ethanol).

Compound	Structure
Methane	CH4
Ethane	C2H6
Methanol	CH3OH
Ethanol	C2H5OH

Additional info:

• These notes cover foundational topics in atomic structure, periodic table organization, chemical formulas, ions, and nomenclature, suitable for General Chemistry students.