Chemistry: Formulas, Elements & Compounds

• These notes cover essential concepts in chemistry.

Empirical and Molecular Formulas

• Empirical formulas represent the simplest whole-number ratio of atoms in a compound.
• Molecular formulas indicate the actual number of atoms of each element in a molecule.
• To calculate empirical formulas, convert mass percentages to moles, divide by the smallest mole value, and find the simplest whole number ratio.
• To find molecular formulas, divide the molecular weight by the empirical formula weight to get a multiplier, then apply it to the empirical formula subscripts.

Periodic Table Elements

• Metals are typically lustrous, conductive, and malleable, located on the left side of the periodic table.
• Nonmetals lack metallic properties and reside on the right side of the table.
• Metalloids (semimetals) exhibit properties of both metals and nonmetals, found along the stair-step line.

Naming and Writing Ionic Compounds

• Ionic compounds consist of a metal and a nonmetal or polyatomic ions.
• Name ionic compounds by stating the metal cation first, followed by the nonmetal anion with an "-ide" ending.
• Polyatomic ions have specific names (e.g., sulfate, nitrate, ammonium).
• For transition metals with multiple oxidation states, use Roman numerals to indicate the charge (e.g., iron(II) chloride).

Molarity and Dilution

• Molarity (M) is defined as moles of solute per liter of solution (M = n/V).
• The dilution equation is M1V1 = M2V2, which is vital for calculating concentrations after dilution.

Significant Figures

• Non-zero digits are always significant.
• Zeros between non-zero digits are significant.
• Leading zeros are not significant.
• Trailing zeros in a number containing a decimal point are significant.
• Exact numbers (counted or defined) have infinite significant figures.

Chemical Equations

• Chemical equations represent chemical reactions using symbols and formulas.
• Balancing chemical equations ensures that the number of atoms for each element is the same on both sides of the equation, obeying the law of conservation of mass.

Stoichiometry

• Stoichiometry involves using balanced chemical equations to calculate the amounts of reactants and products in a chemical reaction.
• To convert mass to moles, use the equation: moles = mass / molar mass.

Percent Yield and Limiting Reactant

• Percent yield is the ratio of actual yield to theoretical yield, multiplied by 100.
• The limiting reactant is the reactant that is completely consumed in a reaction, determining the maximum amount of product formed.
• Excess reagent is the reactant present in more than the required amount to react with the limiting reactant.

Covalent Compounds

• Covalent compounds are formed by sharing electrons between nonmetals.
• Use prefixes (mono-, di-, tri-, etc.) to indicate the number of atoms of each element in the compound (e.g., dinitrogen pentoxide).

Solubility Rules

• Solubility rules predict whether a compound will dissolve in water.
• Common rules include: all nitrates, acetates, and alkali metal compounds are soluble.

Atomic Elements

• Monoatomic elements exist as single atoms (e.g., He, Ne).
• Diatomic elements exist as molecules of two atoms (e.g., H2, O2, Cl2).
• Tetratomic elements exist as molecules of four atoms (e.g. P4).
• Octatomic elements exist as molecules of eight atoms (e.g., S8).

Precipitation Reactions

• Precipitation reactions occur when two aqueous solutions are mixed, resulting in the formation of an insoluble solid (precipitate).
• Use solubility rules to determine if a precipitate will form.

Types of Chemical Reactions

• Combination (synthesis) reactions involve the formation of a single product from two or more reactants.
• Decomposition reactions involve the breakdown of a single reactant into two or more products.
• Single replacement reactions involve one element replacing another in a compound.
• Double replacement (metathesis) reactions involve the exchange of ions between two compounds.
• Combustion reactions involve the rapid reaction between a substance and oxygen, producing heat and light.

History of Atomic Structure

• Dalton's Atomic Theory: proposed that all matter is composed of indivisible atoms.
• Thomson's Plum Pudding Model: discovered electrons and proposed a model with electrons embedded in a positive sphere.
• Rutherford's Gold Foil Experiment: led to the nuclear model of the atom with a small, dense, positive nucleus.
• Bohr's Model: introduced quantized energy levels for electrons.
• Quantum Mechanical Model: describes electrons in terms of probabilities and orbitals.

Oxidizing and Reducing Agents

• Oxidation is the loss of electrons, and reduction is the gain of electrons (OIL RIG).
• The oxidizing agent is the substance that causes oxidation and is itself reduced.
• The reducing agent is the substance that causes reduction and is itself oxidized.

Ionic vs. Covalent Compounds

• Ionic compounds are formed through the transfer of electrons, typically between a metal and a nonmetal.
• Covalent compounds are formed through the sharing of electrons, typically between two nonmetals.

Isotopes

• Isotopes are atoms of the same element with different numbers of neutrons, leading to different mass numbers.

Metric Conversions

• Use conversion factors to convert between metric units (e.g., 1 km = 1000 m, 1 g = 1000 mg).

Activity Series

• The activity series ranks elements in order of their reactivity.
• Elements higher in the series can replace elements lower in the series in a single replacement reaction.

Exact vs. Measured Numbers

• Exact numbers have defined or counted values (e.g., 12 inches in a foot).
• Measured numbers have uncertainty and are obtained through measurement.

Naming Acids

• Binary acids (H + nonmetal) are named with the prefix "hydro-" and the suffix "-ic" (e.g., hydrochloric acid).
• Oxyacids (H + polyatomic ion) are named based on the polyatomic ion. If the ion ends in "-ate," the acid ends in "-ic." If the ion ends in "-ite," the acid ends in "-ous" (e.g., sulfuric acid, sulfurous acid).

Avogadro's Number

• Avogadro's number (6.022 x 10^23) is the number of entities (atoms, molecules, ions, etc.) in one mole.
• Moles = Number of entities / Avogadro's number

Solution Stoichiometry

• In solution stoichiometry, molarity is used to convert between volume of a solution and moles of solute.

Net Ionic Equations

• Net ionic equations show only the species that participate in a reaction.
• Spectator ions (ions that do not change during the reaction) are not included.

Electrolytes

• Strong electrolytes dissociate completely into ions in solution, conducting electricity well.
• Weak electrolytes only partially dissociate, conducting electricity poorly.
• Nonelectrolytes do not dissociate and do not conduct electricity.

Acid-Base Titration

• Titration is a technique used to determine the concentration of an acid or base by neutralizing it with a solution of known concentration.
• Use stoichiometry to find the unknown concentration.

Unit Conversions

• Use conversion factors to convert between different units (e.g., metric to metric, metric to English).

Notes on empirical and molecular formulas, including calculation methods. Overview of the periodic table elements: metals, nonmetals, and metalloids. Explains how to name and write ionic compounds.