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

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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 (neutral), 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	0.00055

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.

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

Atomic mass unit (amu): Standard unit for atomic masses.

Atomic Mass and Isotopes

Calculating Subatomic Particles in Isotopes

To determine the number of protons, neutrons, and electrons in an atom or ion:

Protons (p+): Equal to atomic number (Z)
Neutrons (n0):
Electrons (e-): Equal to protons in a neutral atom; adjust for charge in ions

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

Average Atomic Mass (Atomic Weight)

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

Formula:
Example for carbon:

The Periodic Table

Organization and Groups

The periodic table arranges elements in order of increasing atomic number (Z). Elements are grouped into periods (rows) and groups (columns/families).

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

Nonmetals: Located on the right/top side of the table (except H)
Metalloids: Border the stair-step line; have properties of both metals and nonmetals
Metals: Most elements are metals; found on the left side

Chemical Formulas and Molecules

Molecules and Compounds

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

Diatomic molecules: H2, N2, O2, F2, Cl2, Br2, I2
Molecular compounds: Composed of different atoms (e.g., CH4, CO2, H2O)

Types of 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 Formulas and Models

Structural formulas: Show the order in which atoms are bonded
Perspective drawings: Use wedges/dashed lines 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 of Ions

If electrons are added or removed from a neutral atom, an ion is formed.
Cations: Positively charged ions (loss of electrons)
Anions: Negatively charged ions (gain of electrons)

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 (e.g., NaCl)
Ionic compounds are electrically neutral

Formula of Ionic Compounds

Charge on cation becomes subscript on anion and vice versa
Reduce subscripts to lowest whole-number ratio

Ions	Formula
Na+, Cl-	NaCl
Mg2+, N3-	Mg3N2

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: End in -ide (e.g., Cl- = chloride ion)
Polyatomic anions: End in -ate or -ite (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

Acid Nomenclature

If the anion ends in -ide, the acid name ends in -ic and adds prefix hydro- (e.g., HCl = hydrochloric acid)
If the anion ends in -ite, the acid name ends in -ous (e.g., H2SO3 = sulfurous acid)
If the anion ends in -ate, the acid name ends in -ic (e.g., H2SO4 = sulfuric acid)

Anion	Name	Acid	Name
Cl-	chloride	HCl	hydrochloric acid
SO42-	sulfate	H2SO4	sulfuric acid
NO2-	nitrite	HNO2	nitrous acid

Binary Molecular Compounds

Composed of two nonmetals
Element farthest left on periodic table written first (exceptions: NH3, compounds with O and halogens)
Prefixes denote number of atoms: mono-, di-, tri-, tetra-, penta-, hexa-, hepta-, octa-, nona-, deca-
Second element ends in -ide

Prefix	Number
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: Compounds with only carbon and hydrogen
Alkanes: Simplest hydrocarbons, end in -ane (e.g., methane, ethane, propane, butane)
Alcohols: Formed by replacing a hydrogen atom in an alkane with an -OH group; names end in -ol (e.g., methanol, ethanol)

Compound	Formula
Methane	CH4
Ethane	C2H6
Propane	C3H8
Butane	C4H10
Methanol	CH3OH
Ethanol	C2H5OH

Examples and Applications

Calculate numbers of subatomic particles in isotopes and ions
Determine empirical and molecular formulas
Predict ionic charges based on periodic table group
Name and write formulas for ionic, molecular, and organic compounds

Additional info: These notes cover foundational topics in atomic structure, periodic table organization, chemical formulas, and nomenclature, suitable for General Chemistry students preparing for exams or coursework.