Comprehensive Study Notes for General Chemistry: Atoms, Reactions, Solutions, and Biochemistry

Atoms and Atomic Theory

Atomic Structure and Elements

The concept of the atom is fundamental to chemistry. Atoms are the smallest units of matter that retain the properties of an element.

• Atom: The basic unit of a chemical element, composed of protons, neutrons, and electrons.

• Element: A pure substance consisting of only one type of atom, defined by its atomic number.

• Atomic Number (Z): The number of protons in the nucleus of an atom, which determines the element's identity.

• Isotopes: Atoms of the same element with different numbers of neutrons, resulting in different mass numbers.

• Atomic Weight: The weighted average mass of the isotopes of an element, measured in atomic mass units (amu).

Example: Carbon has atomic number 6. Its common isotopes are carbon-12 and carbon-14.

The Periodic Table and Electronic Structure

Organization and Properties

The periodic table arranges elements by increasing atomic number and groups elements with similar chemical properties.

• Groups: Vertical columns; elements in the same group have similar valence electron configurations.

• Periods: Horizontal rows; properties change progressively across a period.

• Electronic Structure: The arrangement of electrons in an atom's shells and subshells.

• Electron Configuration: The distribution of electrons among the orbitals of an atom.

Example: The electron configuration of sodium (Na, Z=11) is $1s^2\ 2s^2\ 2p^6\ 3s^1$.

Chemical Reactions

Classification and Balancing

Chemical reactions involve the transformation of reactants into products. They are classified by the changes that occur.

• Synthesis (Combination): Two or more substances combine to form one product.

• Decomposition: A single compound breaks down into two or more products.

• Single Replacement: An element replaces another in a compound.

• Double Replacement: Exchange of ions between two compounds.

• Combustion: A substance reacts with oxygen, releasing energy.

• Acid-Base (Neutralization): Acid reacts with base to form water and a salt.

• Redox Reactions: Involve transfer of electrons; oxidation is loss, reduction is gain of electrons.

Balancing Equations: The law of conservation of mass requires that the number of atoms of each element is the same on both sides of the equation.

Mole and Mass Relationships

The Mole Concept

The mole is a counting unit in chemistry, relating the mass of a substance to the number of particles it contains.

• Mole (mol): $6.022 \times 10^{23}$ particles (Avogadro's number).

• Gram–Mole Conversions: $\text{Moles} = \frac{\text{Mass (g)}}{\text{Molar Mass (g/mol)}}$

Example: 18 g of water ($H_2O$) is 1 mole, since the molar mass is 18 g/mol.

Reaction Rates and Chemical Equilibria

Endothermic and Exothermic Reactions

Chemical reactions can absorb or release energy.

• Endothermic: Absorbs heat ($\Delta H > 0$).

• Exothermic: Releases heat ($\Delta H < 0$).

Factors Affecting Reaction Rates

• Concentration of reactants

• Temperature

• Presence of a catalyst

• Surface area

Chemical Equilibrium

• At equilibrium, the rates of the forward and reverse reactions are equal.

• Equilibrium Constant ($K$): $K = \frac{[\text{products}]}{[\text{reactants}]}$ (for a given reaction at constant temperature)

Nuclear Chemistry

Radioactivity and Decay

Nuclear chemistry studies changes in atomic nuclei, including radioactivity.

• Alpha Decay ($\alpha$): Emission of a helium nucleus ($^4_2He$).

• Beta Decay ($\beta$): Conversion of a neutron to a proton with emission of an electron.

• Gamma Decay ($\gamma$): Emission of high-energy photons.

• Conservation Laws: Nucleon number and charge are conserved in nuclear reactions.

• Law of Radioactive Decay: $N = N_0 e^{-\lambda t}$

• Half-life ($t_{1/2}$): Time required for half the nuclei in a sample to decay.

Physical Quantities and Measurements

Metric System and Units

• Length: Meter (m)

• Mass: Gram (g)

• Volume: Liter (L)

Significant Figures

• Indicate the precision of a measurement.

• Rules for determining significant digits in calculations.

Chemical Calculations

Mole Concept and Chemical Formulas

• Relate moles to mass, volume, and number of particles.

• Use chemical formulas to determine the composition of compounds.

Stoichiometry

• Calculations involving chemical equations to determine the amounts of reactants and products.

• Volume and concentration calculations for solutions: $M = \frac{n}{V}$, where $M$ is molarity, $n$ is moles, $V$ is volume in liters.

Solutions

Mixtures and Solutions

• Mixture: Physical combination of substances.

• Solution: Homogeneous mixture of solute and solvent.

• Electrolytes: Substances that conduct electricity when dissolved in water.

Units of Concentration

• Molarity (M): $M = \frac{\text{moles of solute}}{\text{liters of solution}}$

• Dilution: $M_1V_1 = M_2V_2$

Acids and Bases

Definitions and Properties

• Acid: Substance that donates protons ($H^+$) in aqueous solution.

• Base: Substance that accepts protons or donates $OH^-$ ions.

• pH: $pH = -\log[H^+]$

• Common acids: HCl, H$_2$SO$_4$; common bases: NaOH, KOH.

Alcohols

Structure, Naming, and Properties

• Alcohol: Organic compound with a hydroxyl group (-OH) attached to a carbon atom.

• Naming: Based on the parent hydrocarbon, replacing the -e ending with -ol (e.g., ethanol).

• Properties: Polar, can form hydrogen bonds, generally soluble in water.

• Acidity: Alcohols are weak acids.

• Reactions: Can undergo oxidation, dehydration, and substitution reactions.

Amino Acids and Proteins

Structures and Properties

• Amino Acid: Organic molecule with both amino (-NH$_2$) and carboxyl (-COOH) groups.

• Acid–Base Properties: Can act as acids or bases; exist as zwitterions at physiological pH.

• Proteins: Polymers of amino acids linked by peptide bonds; have diverse chemical properties and functions.

Enzymes and Vitamins

Catalysis and Biological Roles

• Enzyme: Biological catalyst that speeds up chemical reactions in living organisms.

• Mechanism: Enzymes lower activation energy and are highly specific.

• Vitamins: Organic compounds required in small amounts for normal metabolism.

• Minerals: Inorganic nutrients essential for health.

Carbohydrates

Classification and Structure

• Monosaccharides: Simple sugars (e.g., glucose).

• Disaccharides: Two monosaccharides linked (e.g., sucrose).

• Polysaccharides: Long chains of monosaccharides (e.g., starch, cellulose).

• D and L Families: Refers to the configuration of the asymmetric carbon farthest from the carbonyl group.

• Properties: Soluble in water, provide energy, structural roles.

Lipids

Structure and Classification

• Lipids: Hydrophobic biomolecules including fats, oils, and steroids.

• Fatty Acids: Long hydrocarbon chains with a carboxyl group.

• Esters: Formed from fatty acids and alcohols (e.g., triglycerides).

• Properties: Insoluble in water, energy storage, insulation.

Nucleic Acids and Protein Synthesis

DNA, RNA, and Genetic Information

• DNA: Deoxyribonucleic acid, stores genetic information.

• Chromosomes: Structures containing DNA and proteins.

• Nucleic Acids: Polymers of nucleotides (sugar, phosphate, base).

• Watson–Crick Model: DNA is a double helix with complementary base pairing (A-T, G-C).

Example: The sequence of bases in DNA determines the sequence of amino acids in proteins.