Fundamental Concepts of Chemistry

Atoms and Elements
- Atoms: Basic unit of matter, consisting of protons, neutrons, and electrons.
- Elements: Pure substances made of only one type of atom, represented by symbols (e.g., H for hydrogen).
Molecules and Compounds
- Molecules: Groups of two or more atoms bonded together (e.g., O₂).
- Compounds: Substances formed from two or more different elements chemically bonded (e.g., H₂O).
Chemical Bonds
- Ionic Bonds: Formed through the transfer of electrons from one atom to another.
- Covalent Bonds: Formed by the sharing of electrons between atoms.
- Metallic Bonds: Involve the pooling of electrons among a lattice of metal atoms.

Solids
- Definite shape and volume.
- Particles are closely packed and vibrate in place.
Liquids
- Definite volume but take the shape of their container.
- Particles are close together but can move past one another.
Gases
- No definite shape or volume; expand to fill their container.
- Particles are far apart and move freely.

Types of Reactions
- Synthesis: Two or more reactants combine to form a product (A + B → AB).
- Decomposition: A single compound breaks down into two or more products (AB → A + B).
- Single Replacement: One element replaces another in a compound (A + BC → AC + B).
- Double Replacement: Exchange of ions between two compounds (AB + CD → AD + CB).
Balancing Equations
- Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction.
- Coefficients are used to balance the number of atoms on both sides of the equation.

Organization
- Arranged by increasing atomic number.
- Groups (columns) indicate elements with similar properties.
- Periods (rows) indicate energy levels of electrons.
Key Groups
- Alkali Metals (Group 1): Highly reactive, one valence electron.
- Transition Metals: D-block elements with variable oxidation states.
- Halogens (Group 17): Very reactive nonmetals, seven valence electrons.
- Noble Gases (Group 18): Inert gases with complete valence shells.

Acids
- Substances that donate protons (H⁺) in solution.
- Sour taste, pH < 7.
Bases
- Substances that accept protons or donate hydroxide ions (OH⁻).
- Bitter taste, slippery feel, pH > 7.
pH Scale
- Measures the acidity or basicity of a solution from 0 (acidic) to 14 (basic), with 7 being neutral.

Enthalpy (ΔH)
- Measure of heat content in a system.
- Exothermic: Releases heat (ΔH < 0).
- Endothermic: Absorbs heat (ΔH > 0).
Entropy (ΔS)
- Measure of disorder or randomness in a system.
- Systems tend to move towards higher entropy.
Free Energy (G)
- Gibbs Free Energy (ΔG): Determines spontaneity of a reaction.
- ΔG < 0: Reaction is spontaneous.
- ΔG > 0: Reaction is non-spontaneous.

Atoms are the fundamental units of matter, composed of protons, neutrons, and electrons.
Elements are pure substances consisting of a single type of atom, represented by symbols (e.g., H for hydrogen).
Molecules are formed when two or more atoms bond together, such as O₂.
Compounds consist of two or more different elements chemically bonded, e.g., H₂O.
Ionic bonds result from the transfer of electrons between atoms, while covalent bonds involve sharing electrons.
Metallic bonds arise from a collective pool of electrons surrounding metal atoms.

Solids have a fixed shape and volume, with closely packed particles that vibrate in place.
Liquids maintain a definite volume but adapt to the shape of their container, allowing particles to move past one another.
Gases possess neither defined shape nor volume, expanding to fill any container with particles that move freely.

Synthesis reactions combine two or more reactants into a product (A + B → AB).
Decomposition reactions involve a single compound breaking down into multiple products (AB → A + B).
Single replacement reactions replace one element in a compound (A + BC → AC + B).
Double replacement reactions involve an exchange of ions between two compounds (AB + CD → AD + CB).
The Law of Conservation of Mass states that mass is conserved in chemical reactions; equilibrating reactions requires the use of stoichiometric coefficients to balance atoms on both sides.

Elements are organized by increasing atomic number, with groups indicating similar properties and periods indicating electron energy levels.
Alkali Metals (Group 1) are highly reactive elements with one valence electron.
Transition Metals exhibit variable oxidation states and are located in the D-block of the periodic table.
Halogens (Group 17) are very reactive nonmetals characterized by seven valence electrons.
Noble Gases (Group 18) are inert, possessing complete valence electron shells.

Acids are substances that donate protons (H⁺) in a solution, characterized by a sour taste and a pH less than 7.
Bases are substances that accept protons or donate hydroxide ions (OH⁻), noted for a bitter taste, slippery texture, and a pH greater than 7.
The pH scale measures the acidity or basicity of a solution, ranging from 0 (most acidic) to 14 (most basic), with 7 representing neutrality.

Enthalpy (ΔH) quantifies heat content in systems; exothermic reactions release heat (ΔH < 0) while endothermic reactions absorb heat (ΔH > 0).
Entropy (ΔS) indicates the degree of disorder in a system; systems naturally progress toward increased entropy.
Gibbs Free Energy (ΔG) determines the spontaneity of reactions, with ΔG < 0 signifying spontaneity and ΔG > 0 indicating non-spontaneity.