Atoms and Atomic Theory

Atoms

Atoms are the fundamental units of matter, representing the smallest particles of an element that retain its chemical properties. Each atom consists of three primary subatomic particles:

• Protons: Positively charged particles located in the nucleus.

• Neutrons: Neutral particles also found in the nucleus.

• Electrons: Negatively charged particles that orbit the nucleus in defined regions called shells or orbitals.

The arrangement and number of these particles determine the atom's identity and chemical behavior.

Atomic Theory

The concept of atoms has evolved over time:

• Democritus (ancient Greece): Proposed indivisible particles called "atomos."

• John Dalton (19th century): Formalized atomic theory, stating that all matter is composed of atoms, atoms of an element are identical, and chemical reactions involve rearrangement of atoms.

• J.J. Thomson: Discovered the electron, leading to the "plum pudding" model.

• Ernest Rutherford: Demonstrated the existence of a dense, positively charged nucleus.

• Niels Bohr: Introduced quantized electron orbits.

• Modern quantum mechanics: Describes electrons as existing in probabilistic orbitals.

Elements and Atomic Number

An element is a pure substance consisting of only one type of atom, defined by its atomic number (number of protons in the nucleus). The atomic number determines the element's identity and its position in the periodic table. In a neutral atom, the number of electrons equals the number of protons.

Isotopes and Atomic Weight

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons, resulting in different atomic masses. The atomic weight of an element is the weighted average of the masses of its naturally occurring isotopes, reflecting their relative abundances.

• Example: Carbon has three isotopes—carbon-12, carbon-13, and carbon-14.

The Periodic Table and Electronic Structure

The Periodic Table

The periodic table organizes all known elements by increasing atomic number, electron configuration, and recurring chemical properties. Elements are arranged in periods (rows) and groups (columns). Elements in the same group have similar chemical properties due to the same number of valence electrons.

• Group 1: Alkali Metals – Highly reactive, one valence electron.

• Group 2: Alkaline Earth Metals – Two valence electrons, less reactive than Group 1.

• Groups 3–12: Transition Metals – Variable oxidation states, form colorful compounds.

• Group 17: Halogens – Highly reactive nonmetals, seven valence electrons.

• Group 18: Noble Gases – Inert, full valence shells.

Electronic Structure and Electron Configurations

Electrons occupy energy levels (shells) around the nucleus. Each shell can hold a maximum number of electrons, given by , where is the shell number. Subshells (s, p, d, f) have specific capacities:

• s: 2 electrons

• p: 6 electrons

• d: 10 electrons

• f: 14 electrons

The electron configuration of an atom describes the distribution of electrons among these subshells.

Electron Configurations and the Periodic Table

The periodic table reflects periodicity in electron configurations. Elements in the same group have similar outer electron configurations, influencing their chemical behavior. The table is divided into blocks (s, p, d, f) based on the subshell being filled.

Electron-Dot (Lewis) Symbols

Lewis symbols represent valence electrons as dots around the element's symbol, helping visualize bonding in molecules and ions.

Ionic Compounds and Acids/Bases

Ionic Compounds and the Octet Rule

Ionic compounds form when electrons are transferred from one atom to another, creating oppositely charged ions held together by electrostatic forces (ionic bonds). The octet rule states that atoms tend to gain, lose, or share electrons to achieve a stable configuration with eight valence electrons.

• Cations: Positively charged ions (formed by losing electrons; typically metals).

• Anions: Negatively charged ions (formed by gaining electrons; typically nonmetals).

Periodic Properties and Naming Ionic Compounds

• Metals in Groups 1, 2, and 13 form cations by losing electrons.

• Nonmetals in Groups 15, 16, and 17 form anions by gaining electrons.

• Naming: Cation first (element name), anion second (root + "-ide"). For transition metals, specify charge with Roman numerals.

Properties of Ionic Compounds

• High melting and boiling points

• Crystalline structure

• Conduct electricity when molten or dissolved in water

• Soluble in water

H+ and OH− Ions: Acids and Bases

• Acids: Increase H+ concentration in solution

• Bases: Increase OH− concentration in solution

• pH is determined by the balance of H+ and OH− ions

Molecular Compounds and Covalent Bonding

Molecular Compounds and Covalent Bonds

Molecular compounds are formed by covalent bonds, where atoms share electrons to achieve stability. Typically, these compounds form between nonmetals.

• Group 14: Four covalent bonds (e.g., carbon)

• Group 15: Three covalent bonds (e.g., nitrogen)

• Group 16: Two covalent bonds (e.g., oxygen)

• Group 17: One covalent bond (e.g., fluorine)

Characteristics of Molecular Compounds

• Low melting and boiling points

• Poor electrical conductivity

• Diverse structures and shapes

Molecular Formulas and Lewis Structures

• Molecular formula: Indicates the number and type of atoms

• Lewis structure: Shows valence electrons and bonding

Polar Covalent Bonds, Electronegativity, and Polar Molecules

• Polar covalent bond: Unequal sharing of electrons due to differences in electronegativity

• Polar molecules: Have a net dipole moment (e.g., water)

• Nonpolar molecules: Symmetrical or have nonpolar bonds (e.g., methane)

Naming Binary Molecular Compounds

• First element: Full name

• Second element: Root + "-ide"

• Prefixes: mono-, di-, tri-, tetra-, etc.

• Example: CO2 is carbon dioxide

Chemical Reactions and Stoichiometry

Classification of Chemical Reactions

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

• Decomposition: One compound breaks into simpler substances

• Single Replacement: One element replaces another in a compound

• Double Replacement: Two compounds exchange ions

• Combustion: Substance reacts with oxygen, releasing energy

• Neutralization: Acid reacts with base to form salt and water

• Redox: Involves electron transfer (oxidation and reduction)

Chemical Equations and Balancing

• Balanced equations have equal numbers of each atom on both sides

• Steps: Write unbalanced equation, count atoms, use coefficients to balance, verify

Acids, Bases, and Neutralization

• Acids: Release H+ ions

• Bases: Release OH− ions

• Neutralization: Acid + Base → Salt + Water

Redox Reactions

• Oxidation: Loss of electrons

• Reduction: Gain of electrons

The Mole and Mass Relationships

The Mole and Avogadro’s Number

• 1 mole = entities (Avogadro’s number)

• Links atomic/molecular scale to measurable quantities

Gram–Mole Conversions

• Molar mass: Mass of 1 mole of a substance (g/mol)

• To convert grams to moles:

• To convert moles to grams:

Reaction Rates and Chemical Equilibria

Endothermic and Exothermic Reactions

• Exothermic: Release energy (e.g., combustion)

• Endothermic: Absorb energy (e.g., photosynthesis)

Factors Influencing Reaction Rates

• Concentration: Higher concentration increases rate

• Temperature: Higher temperature increases rate

• Surface area: Greater area increases rate

• Catalysts: Lower activation energy, increase rate

• Nature of reactants: Chemical structure affects rate

Chemical Equilibrium and Equilibrium Constants

• At equilibrium, forward and reverse reaction rates are equal

• Equilibrium constant ():

• : Products favored; : Reactants favored

Nuclear Chemistry

Radioactivity

• Spontaneous emission of particles/energy from unstable nuclei

• Types: Alpha (α), Beta (β), Gamma (γ) decay

• Medical applications: Radiotherapy, imaging, tracers

Radioactive Half-Life

• Time for half of a radioactive sample to decay

• Formula:

Physical Quantities and Measurement

Metric System and Units

• Length: meter (m), centimeter (cm), millimeter (mm), kilometer (km)

• Mass: kilogram (kg), gram (g), milligram (mg), microgram (μg)

• Volume: liter (L), milliliter (mL), cubic centimeter (cm3)

Significant Figures

• Reflect measurement precision

• Rules: All nonzero digits significant; zeros between nonzero digits significant; leading zeros not significant; trailing zeros significant if decimal present

Fundamental Chemical Laws

• Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction.

• Law of Definite Proportions: A compound always contains the same elements in the same ratio by mass.

• Law of Multiple Proportions: When two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in small whole-number ratios.

Chemical Calculations

Mole Concept and Chemical Formulas

• 1 mole = entities

• Molar mass: Mass of 1 mole of a substance

Stoichiometry

• Use balanced equations to relate moles of reactants and products

• Steps: Convert to moles, use mole ratios, convert to desired units

Volume and Concentration Calculations

• Molarity ():

• Dilution:

Solutions and Electrolytes

Mixtures and Solutions

• Homogeneous: Uniform composition (solutions)

• Heterogeneous: Non-uniform composition

Units of Concentration

• Molarity (M), mass/volume percent (% m/v), parts per million (ppm), molality (m)

Dilution

• Formula:

Ions in Solution: Electrolytes

• Electrolytes: Substances that dissociate into ions in water

• Strong electrolytes: Complete dissociation (e.g., NaCl)

• Weak electrolytes: Partial dissociation (e.g., acetic acid)

• Non-electrolytes: No dissociation (e.g., glucose)

Acids, Bases, and Buffers

Acids and Bases in Aqueous Solution

• Acids: Release H+ ions

• Bases: Release OH− ions

• pH scale: 0 (acidic) to 14 (basic), 7 is neutral

Brønsted–Lowry Definition

• Acid: Proton donor

• Base: Proton acceptor

Acid Dissociation Constant () and Strength

• Strong acids/bases: Complete dissociation

• Weak acids/bases: Partial dissociation

Acid-Base Reactions and Salt Solutions

• Neutralization: Acid + Base → Salt + Water

• Salts can be neutral, acidic, or basic depending on their parent acid/base

Buffers and pH Measurement

• Buffer: Solution that resists pH changes, typically a weak acid and its conjugate base

• pH:

• Henderson–Hasselbalch equation:

Introduction to Organic Chemistry

Alkanes

• Saturated hydrocarbons (single bonds), general formula

• Isomers: Same formula, different structures

• Naming: Longest chain, number substituents, use prefixes

• Properties: Nonpolar, low reactivity, insoluble in water

• Reactions: Combustion, halogenation

Alkenes and Alkynes

• Alkenes: At least one double bond (), general formula

• Alkynes: At least one triple bond (), general formula

• Cis–trans isomerism in alkenes

• Reactions: Addition (hydrogenation, halogenation, hydration)

Aromatic Compounds

• Benzene: Six-membered ring with delocalized π-electrons

• Aromaticity: Cyclic, planar, conjugated, follows Hückel’s rule ( π-electrons)

• Naming: Substituents on benzene ring (ortho, meta, para)

• Reactions: Electrophilic aromatic substitution (halogenation, nitration, sulfonation)

Alcohols and Phenols

• Alcohols: Contain –OH group attached to saturated carbon

• Phenols: –OH group attached to aromatic ring

• Naming: Replace "-e" with "-ol"

• Properties: Hydrogen bonding, higher boiling points, weak acidity

• Reactions: Oxidation, dehydration, esterification

Ethers, Thiols, Disulfides, and Halogenated Compounds

• Ethers: R–O–R', relatively inert, good solvents

• Thiols: R–SH, strong odors, form disulfides (R–S–S–R')

• Disulfides: Important in protein structure

• Halogenated compounds: R–X, used in solvents, anesthetics, and pharmaceuticals

Amines and Amine Salts

• Amines: Derived from ammonia, classified as primary, secondary, tertiary

• Basicity: Due to lone pair on nitrogen

• Amine salts: Formed by reaction with acids, more water-soluble

• Heterocyclic amines: Nitrogen in ring structure (e.g., pyridine)

Aldehydes and Ketones

• Aldehydes: Carbonyl group (C=O) at end of chain

• Ketones: Carbonyl group within chain

• Naming: Aldehydes (-al), ketones (-one)

• Reactions: Oxidation (aldehydes to acids), reduction (to alcohols)

Carboxylic Acids and Derivatives

• Carboxylic acids: –COOH group, weak acids

• Derivatives: Esters (–COOR), amides (–CONH2), anhydrides

• Reactions: Esterification, amide formation, hydrolysis

Amino Acids and Proteins

• Amino acids: Contain amino (–NH2) and carboxyl (–COOH) groups

• Zwitterions: Both positive and negative charges at physiological pH

• Peptide bonds: Link amino acids in proteins

• Protein structure: Primary, secondary, tertiary, quaternary

Enzymes and Vitamins

• Enzymes: Biological catalysts, highly specific

• Vitamins: Organic compounds, essential in small amounts

• Minerals: Inorganic elements, required for physiological processes

Carbohydrates

• Monosaccharides: Simple sugars (glucose, fructose)

• Disaccharides: Two monosaccharides (sucrose, lactose, maltose)

• Polysaccharides: Long chains (starch, glycogen, cellulose)

• Reducing sugars: Free aldehyde or ketone group

Lipids

• Simple lipids: Fats (triglycerides), waxes

• Complex lipids: Phospholipids, glycolipids

• Derived lipids: Steroids, fat-soluble vitamins

• Fatty acids: Saturated (no double bonds), unsaturated (one or more double bonds)

• Properties: Hydrophobic, energy storage, cell membrane structure

Nucleic Acids and Protein Synthesis

• DNA: Stores genetic information, double helix structure

• RNA: Involved in protein synthesis

• Nucleotides: Building blocks (phosphate, sugar, nitrogenous base)

• Base pairing: Adenine–Thymine (A–T), Guanine–Cytosine (G–C)

Additional info: This study guide covers all major topics in introductory college chemistry, including atomic structure, the periodic table, chemical bonding, stoichiometry, states of matter, solutions, acids and bases, organic chemistry, and biochemistry. It is suitable for exam preparation and foundational understanding for further studies in chemistry and related fields.