Basic Concepts of Chemistry

Matter: Anything that has mass and occupies space.
Elements: Pure substances that cannot be broken down into simpler substances (e.g., hydrogen, oxygen).
Compounds: Substances formed when two or more elements chemically bond (e.g., water - H₂O).
Mixtures: Combinations of two or more substances that are not chemically bonded (e.g., air, salad).

Atom: The basic unit of matter, composed of protons, neutrons, and electrons.
- Protons: Positively charged particles found in the nucleus.
- Neutrons: Neutral particles also found in the nucleus.
- Electrons: Negatively charged particles that orbit the nucleus.
Atomic Number: The number of protons in an atom's nucleus; defines the element.
Mass Number: The total number of protons and neutrons in an atom.

Ionic Bonds: Formed when electrons are transferred from one atom to another (e.g., NaCl).
Covalent Bonds: Formed when two atoms share electrons (e.g., O₂).
Metallic Bonds: Occur between metal atoms where electrons are shared in a 'sea' of electrons.

Reactants: Substances that undergo change in a chemical reaction.
Products: New substances formed as a result of a chemical reaction.
Types of Reactions:
- Synthesis: Two or more reactants combine to form a single product (A + B → AB).
- Decomposition: A single compound breaks down into two or more products (AB → A + B).
- Single Replacement: An element replaces another in a compound (A + BC → AC + B).
- Double Replacement: Exchange of ions between two compounds (AB + CD → AD + CB).
- Combustion: A substance reacts with oxygen, releasing energy (usually involves hydrocarbons).

Groups/Families: Vertical columns that contain elements with similar properties (e.g., alkali metals, halogens).
Periods: Horizontal rows that represent energy levels of electrons.
Metals, Nonmetals, and Metalloids:
- Metals: Good conductors, malleable, ductile (e.g., iron, gold).
- Nonmetals: Poor conductors, brittle, diverse properties (e.g., carbon, nitrogen).
- Metalloids: Have properties of both metals and nonmetals (e.g., silicon, arsenic).

Acids: Substances that donate protons (H⁺ ions) in solution (e.g., hydrochloric acid - HCl).
Bases: Substances that accept protons or donate hydroxide ions (OH⁻) in solution (e.g., sodium hydroxide - NaOH).
pH Scale: Measures the acidity or basicity of a solution:
- pH < 7: Acidic
- pH = 7: Neutral
- pH > 7: Basic

Mole: A unit that measures the amount of substance, equivalent to Avogadro's number (6.022 x 10²³ particles).
Molar Mass: The mass of one mole of a substance (g/mol) calculated using the periodic table.
Balanced Chemical Equations: Equations must have the same number of atoms of each element on both sides to obey the law of conservation of mass.

Reaction Rate: The speed at which reactants are converted to products, affected by:
- Concentration
- Temperature
- Surface area
- Catalysts
Chemical Equilibrium: The state where the rate of the forward reaction equals the rate of the reverse reaction.

Hydrocarbons: Compounds composed of hydrogen and carbon (e.g., alkanes, alkenes, alkynes).
Functional Groups: Specific groups of atoms that impart characteristic properties to organic compounds (e.g., hydroxyl -OH, carboxyl -COOH).

These notes cover the fundamental concepts and categories within chemistry, providing a solid foundation for further study.

Matter has mass and occupies space; it constitutes everything around us.
Elements cannot be broken down into simpler substances and include foundational elements like hydrogen and oxygen.
Compounds are formed from the chemical bonding of two or more elements (e.g., water is H₂O).
Mixtures are combinations of substances that retain their individual properties and can be physically separated (e.g., air and salad).

An atom is the smallest unit of matter, comprising protons, neutrons, and electrons.
Protons are positively charged particles located in the nucleus of the atom.
Neutrons are neutral particles found alongside protons in the nucleus.
Electrons are negatively charged particles that orbit the nucleus and are involved in chemical bonding.
The atomic number specifies the number of protons in an atom, determining the element's identity.
The mass number equals the total count of protons and neutrons in an atom.

Ionic bonds arise when electrons are transferred between atoms, resulting in charged ions (e.g., sodium chloride or NaCl).
Covalent bonds form through the sharing of electrons between two atoms (e.g., molecular oxygen or O₂).
Metallic bonds occur among metal atoms, characterized by a 'sea' of delocalized electrons facilitating conductivity.

Reactants are the initial substances that undergo change during a reaction.
Products are the new substances formed as a result of the chemical transformation.
Types of reactions include:
- Synthesis: Two or more reactants form a single product (A + B → AB).
- Decomposition: A single compound breaks down into two or more products (AB → A + B).
- Single Replacement: An element in a compound is replaced by another element (A + BC → AC + B).
- Double Replacement: Ions from two compounds exchange places (AB + CD → AD + CB).
- Combustion: Involves a substance reacting with oxygen, often producing energy, typically involving hydrocarbons.

Groups or families are vertical columns that encompass elements with similar chemical properties (e.g., alkali metals, halogens).
Periods are horizontal rows representing energy levels of electrons surrounding the nucleus.
Metals exhibit good electrical conductivity, malleability, and ductility (e.g., iron, gold).
Nonmetals are generally poor conductors and can be brittle with diverse physical properties (e.g., carbon, nitrogen).
Metalloids possess a blend of properties from both metals and nonmetals (e.g., silicon, arsenic).

Acids donate protons (H⁺ ions) in solutions (e.g., hydrochloric acid - HCl).
Bases accept protons or donate hydroxide ions (OH⁻) in solutions (e.g., sodium hydroxide - NaOH).
The pH scale quantifies acidity or basicity:
- pH < 7 indicates an acidic solution.
- pH = 7 represents a neutral solution.
- pH > 7 denotes a basic solution.

A mole quantifies an amount of substance, equivalent to Avogadro's number (approximately 6.022 x 10²³ particles).
Molar mass indicates the mass of one mole of a substance (expressed in grams per mole, g/mol) and is determined using the periodic table.
Balanced chemical equations obey the law of conservation of mass, ensuring equal atom counts on both sides of the equation.

Exothermic reactions release heat into the surroundings (e.g., combustion).
Endothermic reactions absorb heat from the surroundings (e.g., photosynthesis).
Enthalpy (ΔH) refers to the total heat content within a system, influencing energy changes during reactions.

Reaction rate measures how quickly reactants are converted into products, influenced by factors such as concentration, temperature, surface area, and the presence of catalysts.
Chemical equilibrium exists when the rate of the forward reaction equals the rate of the reverse reaction, achieving a stable state in the reaction mixture.

Hydrocarbons consist solely of carbon and hydrogen atoms and can be categorized into alkanes, alkenes, and alkynes.
Functional groups are specific atom arrangements in organic compounds that confer distinct chemical properties (e.g., hydroxyl -OH, carboxyl -COOH).