Essential Chemistry Notes for High School

Chemical Bonds and Reactions

Atoms connect through three main types of chemical bonds: ionic bonds (between metals and nonmetals), covalent bonds (between nonmetals), and metallic bonds (between metals). The electronegativity difference determines if a bond is nonpolar covalent $0-0.4$, polar covalent $0.41-1.8$, or ionic (>1.8).

When naming compounds, follow specific patterns. Ionic compounds combine cation and anion names (like sodium chloride or iron(III) oxide). Binary covalent compounds use prefixes to show how many atoms are present (like sulfur dioxide). Acids follow patterns like "hydro-" for binary acids (hydrochloric acid) or changing "-ate" to "-ic" for ternary acids.

Chemical reactions come in different types. In combination reactions, substances join together (like Mg + Cl₂ → MgCl₂). Decomposition reactions break compounds apart. Replacement reactions occur when more reactive elements replace less reactive ones. In redox reactions, electrons transfer between substances (remember LEORA GEROA: Loss of Electrons is Oxidation, Reducing Agent; Gain of Electrons is Reduction, Oxidizing Agent).

Chemistry Hack: When predicting reaction products, memorize the patterns! For metal + nonmetal, you'll get a binary ionic compound. For acid + base, you always get a salt + water.

Gas laws describe how gases behave when pressure, volume, temperature, and moles change. Boyle's Law shows pressure and volume are inversely related $P₁V₁ = P₂V₂$. Charles' Law reveals that volume increases with temperature $V₁/T₁ = V₂/T₂$. The Ideal Gas Law (PV = nRT) combines all these relationships.

When working with solutions, you can express concentration in various ways like molarity (moles per liter of solution), molality (moles per kilogram of solvent), or percent by mass. Each concentration unit serves different purposes in chemistry calculations.