Basic Concepts of Chemistry

Definition: Chemistry is the scientific study of matter, its properties, structure, composition, reactions, and changes.
Branches:
- Organic Chemistry: Study of carbon-containing compounds.
- Inorganic Chemistry: Study of inorganic compounds, typically excluding hydrocarbons.
- Physical Chemistry: Focus on the physical properties and behavior of chemical systems.
- Analytical Chemistry: Techniques for analyzing substances to determine composition.
- Biochemistry: Study of chemical processes within living organisms.

States of Matter:
- Solid: Definite shape and volume; particles tightly packed.
- Liquid: Definite volume but takes the shape of its container; particles are less tightly packed than solids.
- Gas: Neither definite shape nor volume; particles are far apart and move freely.
Properties:
- Physical Properties: Characteristics observed without changing the substance (e.g., boiling point, color).
- Chemical Properties: Characteristics that determine how a substance reacts with others (e.g., reactivity with acid).

Atoms: Basic units of matter, composed of protons, neutrons, and electrons.
- Protons: Positively charged particles in the nucleus.
- Neutrons: Neutral particles in the nucleus.
- Electrons: Negatively charged particles surrounding the nucleus.
Atomic Number: Number of protons in an atom, defining the element.
Mass Number: Total number of protons and neutrons in the nucleus.

Ionic Bonds: Formed when electrons are transferred from one atom to another, creating charged ions.
Covalent Bonds: Formed when two atoms share one or more pairs of electrons.
Metallic Bonds: Occur in metals, where electrons are shared freely among a lattice of atoms.

Reactants and Products: Substances that undergo change (reactants) and substances formed (products).
Types of Reactions:
- Synthesis: Two or more reactants combine to form one product.
- Decomposition: A single compound breaks down into two or more products.
- Single Replacement: An element replaces another element in a compound.
- Double Replacement: Exchange of ions between two compounds.
- Combustion: Reaction between a substance and oxygen, usually producing heat and light.

Mole: SI unit used to measure the amount of substance, defined as 6.022 x 10^23 entities (Avogadro's number).
Molar Mass: Mass of one mole of a substance, typically expressed in grams per mole (g/mol).

Solution: A homogeneous mixture of two or more substances.
Solute: Substance dissolved in a solvent.
Solvent: Substance that dissolves the solute.
Concentration: Amount of solute in a given volume of solution, commonly expressed in molarity (M), which is moles of solute per liter of solution.

Acids: Substances that donate protons (H+) in a solution; have a sour taste and turn blue litmus paper red.
Bases: Substances that accept protons or donate hydroxide ions (OH-); have a bitter taste and turn red litmus paper blue.
pH Scale: Measures acidity or basicity; ranges from 0 (acidic) to 14 (basic), with 7 as neutral.

Enthalpy (ΔH): Measure of heat content in a system; changes during chemical reactions.
Exothermic Reactions: Release heat energy; ΔH is negative.
Endothermic Reactions: Absorb heat energy; ΔH is positive.

Groups: Columns; elements in the same group have similar properties.
Periods: Rows; represent energy levels of electrons.
Metals, Nonmetals, Metalloids: Classification of elements based on properties; metals are good conductors, nonmetals are poor conductors, and metalloids have intermediate properties.

Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction.
Law of Definite Proportions: A chemical compound always contains its component elements in fixed ratio by mass.
Law of Multiple Proportions: When two elements form multiple compounds, the ratios of the masses of one element that combines with a fixed mass of the other can be expressed as small whole numbers.

The scientific study of matter, its properties, composition, structure, reactions, and the changes it undergoes.
Major branches include organic, inorganic, physical, analytical, and biochemistry, each focusing on specific aspects of matter and its behavior.

Exists in various states: solid (definite shape and volume), liquid (definite volume, indefinite shape), and gas (indefinite shape and volume). These states are determined by particle arrangement and movement.
Described by physical properties (observable without altering chemical composition, e.g., color, boiling point) and chemical properties (describe how a substance reacts, e.g., reactivity with acid).

Matter consists of atoms, containing protons (positive charge), neutrons (neutral charge) in the nucleus, and electrons (negative charge) in orbitals surrounding the nucleus.
Atomic number defines an element (number of protons). Mass number is the sum of protons and neutrons.
Atoms bond through ionic bonds (electron transfer), covalent bonds (electron sharing), or metallic bonds (electron delocalization in a metal lattice).

Involve reactants (starting materials) transforming into products (resulting substances).
Classified into synthesis, decomposition, single replacement, double replacement, and combustion reactions based on the changes in reactants and products.
The mole (6.022 x 10²³ entities) is a fundamental unit for measuring amounts of substances, with molar mass expressing the mass of one mole of a substance.

Solutions are homogeneous mixtures. A solute dissolves in a solvent resulting in a solution.
Solution concentration (amount of solute per volume of solution) is commonly expressed in molarity (moles of solute per liter of solution).

Acids donate protons (H⁺), taste sour, and turn blue litmus paper red.
Bases accept protons or donate hydroxide ions (OH⁻), taste bitter, and turn red litmus paper blue.
The pH scale (0-14) measures acidity (0-7) and basicity (7-14), with 7 representing neutrality.

Enthalpy (ΔH) measures heat content changes in chemical reactions.
Exothermic reactions release heat (ΔH < 0), while endothermic reactions absorb heat (ΔH > 0).

Organizes elements by atomic number, showing trends in their properties.
Elements are grouped into columns (groups) having similar chemical properties, and rows (periods) reflecting electron energy levels.
Classified into metals (conductive), nonmetals (poorly conductive), and metalloids (intermediate properties).

Law of Conservation of Mass: Mass remains constant in chemical reactions.
Law of Definite Proportions: A compound has a constant composition by mass.
Law of Multiple Proportions: When elements form multiple compounds, mass ratios are simple whole numbers.