Introduction to Chemistry

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Chemistry Basics

• Chemistry is the study of matter, its properties, and how matter changes.
• Matter has mass and occupies space (volume).

Pure Substances

• Pure substances have a fixed composition and distinct properties.
• Elements cannot be broken down into simpler substances by chemical means.
• Compounds consist of two or more elements chemically combined in fixed proportions.

Mixtures

• Mixtures combine two or more substances where each retains its chemical identity.
• Homogeneous mixtures have uniform composition.
• Heterogeneous mixtures do not have uniform composition.

Properties of Matter

• Physical properties are displayed without changing a substance's composition (e.g., boiling point, melting point, density, color, hardness).
• Chemical properties are displayed through changing a substance's composition (e.g., flammability, reactivity with acid, oxidizing ability).

Changes in Matter

• Physical changes alter the form, not the chemical composition (e.g., melting, boiling, dissolving).
• Chemical changes (reactions) alter the chemical composition (e.g., combustion, oxidation, decomposition).

The Scientific Method

• The scientific method provides a systematic approach to research.
• Observations lead to a hypothesis.
• A hypothesis is a testable explanation or prediction.
• Experiments test the hypothesis, and results either support or refute it.
• Scientific laws are concise statements or equations summarizing observations.
• A scientific theory is a well-established explanation incorporating facts, laws, inferences, and tested hypotheses.

States of Matter

• Matter exists as solid, liquid, or gas.
• Solids have definite shape and volume.
• Liquids have definite volume but take the container's shape.
• Gases have no definite shape or volume, expanding to fill the container.

Atomic Structure

• The atom is the smallest unit of an element retaining its chemical properties.
• Atoms contain protons (positive charge), neutrons (no charge), and electrons (negative charge).
• The nucleus contains protons and neutrons.
• Electrons occupy the space around the nucleus.
• The atomic number (Z) is the number of protons.
• The mass number (A) is the total number of protons and neutrons.
• Isotopes are atoms of the same element with different numbers of neutrons.

Chemical Compounds

• Chemical compounds form when atoms combine.
• Ionic compounds form by electron transfer, creating ions (charged species).
• Covalent compounds form by electron sharing.
• A chemical formula represents the composition of a compound.
• A molecular formula shows the actual number of atoms in a molecule.
• An empirical formula shows the simplest whole-number ratio of atoms.
• A structural formula shows the arrangement of atoms and bonds.

Chemical Reactions

• Chemical reactions rearrange atoms and molecules.
• Chemical equations represent reactions using formulas and symbols.
• Balanced equations have the same number of each type of atom on both sides.

Stoichiometry

• Stoichiometry quantifies relationships between reactants and products.
• The mole (mol) is the SI unit for the amount of substance.
• Avogadro's number (NA) is ~6.022 x 10^23 entities per mole.
• Molar mass is the mass of one mole in grams.
• The limiting reactant is completely consumed.
• The excess reactant is present in more than the required amount.
• Theoretical yield is the maximum product formed from the limiting reactant.
• Actual yield is the product obtained from a reaction.
• Percent yield is the (actual yield / theoretical yield) x 100%.

Solutions

• Solutions are homogeneous mixtures.
• A solute is the substance being dissolved.
• A solvent does the dissolving.
• Concentration is the amount of solute in a solvent or solution.
• Molarity (M) is moles of solute per liter of solution.

Acids and Bases

• Acids produce hydrogen ions (H+) in water.
• Bases produce hydroxide ions (OH-) in water.
• pH measures acidity or basicity: 7 is neutral, below 7 is acidic, above 7 is basic.

Redox Reactions

• Oxidation-reduction (redox) reactions transfer electrons.
• Oxidation is the loss of electrons.
• Reduction is the gain of electrons.
• An oxidizing agent causes oxidation and is reduced.
• A reducing agent causes reduction and is oxidized.

Thermochemistry

• Thermochemistry studies heat changes in chemical reactions.
• Energy is the capacity to do work.
• Heat transfers thermal energy between objects at different temperatures.
• Exothermic reactions release heat.
• Endothermic reactions absorb heat.
• Enthalpy (H) is related to heat content.
• The change in enthalpy (ΔH) is the difference between product and reactant enthalpy.
• Hess's law: ΔH is the same whether a reaction occurs in one or multiple steps.

Chemical Kinetics

• Chemical kinetics studies reaction rates.
• Reaction rate is the change in concentration per unit time.
• Factors affecting rate: temperature, concentration, surface area, catalyst.
• A catalyst increases the rate without being consumed.

Chemical Equilibrium

• Chemical equilibrium occurs when forward and reverse rates are equal.
• At equilibrium, reactant and product concentrations are constant.
• Le Chatelier's principle: a system at equilibrium shifts to relieve stress from changes in concentration, temperature, pressure, or volume.

Organic Chemistry

• Organic chemistry studies carbon compounds.
• Carbon forms strong covalent bonds, creating diverse molecules.
• Hydrocarbons contain only carbon and hydrogen.
• Alkanes contain only single bonds.
• Alkenes have at least one double bond.
• Alkynes have at least one triple bond.
• Functional groups dictate chemical reactivity (e.g., alcohols, ethers, aldehydes, ketones, carboxylic acids, esters, amines).
• Polymers are large molecules with repeating units (monomers).
• Polymerization joins monomers to form polymers.
• Important polymers: proteins, carbohydrates, nucleic acids.