chemistry

Atom: The smallest unit of an element that retains the chemical identity of that element. Composed of protons, neutrons, and electrons.
Elements: Pure substances consisting of only one type of atom. They cannot be broken down into simpler substances by chemical means. Represented by chemical symbols (e.g., $H$ , $O$ , $Fe$ ).
Compounds: Substances formed when two or more different elements are chemically bonded together in fixed proportions (e.g., $H_2O$ , $NaCl$ ).
Molecules: Two or more atoms held together by chemical bonds. Can be elements (e.g., $O2$ ) or compounds (e.g., $CO2$ ).

Protons: Positively charged particles ( $+1$ ) found in the nucleus. Determine the atomic number ( $Z$ ).
Neutrons: Neutral particles (no charge) found in the nucleus. Contribute to the mass number but not the charge.
Electrons: Negatively charged particles ( $-1$ ) that orbit the nucleus in electron shells or orbitals. Determine an atom's chemical properties.
Atomic Number ( $Z$ ): Number of protons in an atom. Defines the element.
Mass Number ( $A$ ): Total number of protons and neutrons in an atom's nucleus.
Isotopes: Atoms of the same element (same number of protons) but with different numbers of neutrons (different mass numbers).

Organizes elements by increasing atomic number.
Periods: Horizontal rows (1-7), correspond to the number of electron shells.
Groups/Families: Vertical columns (1-18), elements in the same group have similar chemical properties due to the same number of valence (outermost shell) electrons.
- Alkali Metals (Group 1): Highly reactive metals.
- Alkaline Earth Metals (Group 2): Reactive metals.
- Transition Metals (Groups 3-12): Diverse properties, often form colored compounds.
- Halogens (Group 17): Highly reactive nonmetals, often form salts.
- Noble Gases (Group 18): Unreactive, stable due to full valence shells.

Ionic Bonds: Formed by the transfer of electrons between a metal (loses electrons to become a cation) and a nonmetal (gains electrons to become an anion). Results in electrostatic attraction (e.g., $NaCl$ ).
Covalent Bonds: Formed by the sharing of electrons between two nonmetals.
- Nonpolar Covalent: Equal sharing of electrons (e.g., $O_2$ ).
- Polar Covalent: Unequal sharing of electrons due to differences in electronegativity, creating partial charges (e.g., $H_2O$ ).
Metallic Bonds: Electrostatic attraction between positively charged metal ions and a "sea" of delocalized electrons.

Hydrogen Bonding: Strongest IMF, occurs when hydrogen is bonded to a highly electronegative atom (N, O, F) and attracted to another N, O, or F atom on a different molecule.
Dipole-Dipole Forces: Occur between polar molecules.
London Dispersion Forces (LDFs): Weakest IMF, present in all molecules (polar and nonpolar) due to temporary, induced dipoles.

Represent chemical reactions, showing reactants (left) and products (right).
Must be balanced to obey the Law of Conservation of Mass (same number of each type of atom on both sides):
$2H2(g) + O2(g) \rightarrow 2H_2O(l)$

Synthesis (Combination): $A + B \rightarrow AB$
Decomposition: $AB \rightarrow A + B$
Single Displacement: $A + BC \rightarrow AC + B$
Double Displacement: $AB + CD \rightarrow AD + CB$
Combustion: Reaction with oxygen, often producing heat and light (e.g., hydrocarbon + $O2 \rightarrow CO2 + H_2O$ ).
Acid-Base (Neutralization): Acid + Base $\rightarrow$ Salt + Water.

Mole: A unit of amount; $1 \text{ mole} = 6.022 \times 10^{23}$ particles (Avogadro's number).
Molar Mass: The mass of one mole of a substance (in $g/mol$ ), numerically equal to its atomic/molecular weight.
Mole Ratios: Derived from the coefficients in a balanced chemical equation, used to convert between amounts of reactants and products.
Limiting Reactant: The reactant that is completely consumed in a reaction, determining the maximum amount of product that can be formed.
Theoretical Yield: The maximum amount of product that can be formed from given amounts of reactants.
Percent Yield: $\frac{\text{Actual Yield}}{\text{Theoretical Yield}} \times 100\%$

Solid: Fixed shape and volume, particles vibrate in fixed positions.
Liquid: Fixed volume but takes the shape of its container, particles can slide past each other.
Gas: No fixed shape or volume, particles are far apart and move randomly.
Phase Changes: Melting, freezing, vaporization, condensation, sublimation, deposition.

Solution: A homogeneous mixture of two or more substances.
Solute: The substance present in the lesser amount, dissolved in the solvent.
Solvent: The substance present in the greater amount, dissolves the solute.
Concentration: Amount of solute in a given amount of solvent or solution.
- Molarity ( $M$ ): Moles of solute per liter of solution ( $\frac{\text{mol}}{\text{L}}$ )

Organic Chemistry: The study of carbon-containing compounds.
Hydrocarbons: Compounds composed solely of carbon and hydrogen.
- Alkanes: Single bonds only (e.g., methane, $CH_4$ ).
- Alkenes: At least one carbon-carbon double bond (e.g., ethene, $C2H4$ ).
- Alkynes: At least one carbon-carbon triple bond (e.g., ethyne, $C2H2$ ).
Functional Groups: Specific groups of atoms within a molecule that are responsible for its characteristic chemical reactions (e.g., alcohols ( $-OH$ ), carboxylic acids ( $-COOH$ ), amines ( $-NH_2$ )).