Measurement and Scientific Notation

Scientific Notation and Significant Figures

Scientific notation is used to express very large or very small numbers in a concise format. Significant figures reflect the precision of a measurement.

• Scientific Notation: Numbers are written as , where is a number between 1 and 10, and is an integer.

• Large numbers: Move decimal left, exponent positive (e.g., ).

• Small numbers: Move decimal right, exponent negative (e.g., ).

• Significant Figures: All non-zero digits are significant; zeros between non-zero digits are significant; leading zeros are not significant; trailing zeros are significant only if there is a decimal point.

Accuracy refers to how close a measured value is to the true value. Precision refers to how close repeated measurements are to each other.

Metric System and Unit Conversions

The metric system uses standard prefixes to indicate multiples of units. Unit conversions are essential for solving chemistry problems.

Common conversions: , , .

Atoms, Molecules, and Ions

Classification of Matter

Matter can be classified as elements, compounds, or mixtures.

• Element: Pure substance that cannot be broken down into simpler substances.

• Compound: Substance composed of two or more elements chemically bonded.

• Mixture: Combination of two or more substances physically mixed, not chemically bonded.

Periodic Table Organization

The periodic table arranges elements by atomic number and groups them by similar properties.

• Groups: Vertical columns (e.g., Group 1: Alkali metals, Group 17: Halogens).

• Periods: Horizontal rows.

• Main Group Elements: Groups 1, 2, and 13-18.

• Transition Metals: Groups 3-12.

• Metals: Left side of the table; good conductors, malleable, ductile.

• Nonmetals: Right side; poor conductors, brittle, many are gases.

• Metalloids: Elements with properties intermediate between metals and nonmetals.

Atomic Structure

Atoms consist of protons, neutrons, and electrons. The atomic number (Z) is the number of protons; the mass number (A) is the sum of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Atomic Mass: Weighted average of isotopic masses.

Ion Formation

Main group elements form ions by gaining or losing electrons to achieve a stable electron configuration.

Common Polyatomic Ions

Mass Relationships in Chemical Reactions

Mole Concept and Avogadro's Number

The mole is a counting unit in chemistry, representing particles (Avogadro's number).

• Molar Mass: Mass of one mole of a substance, in grams per mole.

• Conversions: Use molar mass to convert between grams and moles.

Stoichiometry

Stoichiometry involves calculating the amounts of reactants and products in chemical reactions.

• Write and balance chemical equations.

• Use coefficients to relate moles of reactants and products.

• Convert between grams, moles, and number of particles.

Example: For the reaction , 2 moles of hydrogen react with 1 mole of oxygen to produce 2 moles of water.

Percent Composition and Empirical Formulas

Percent composition shows the mass percentage of each element in a compound. Empirical formulas show the simplest whole-number ratio of atoms.

• Percent Composition:

• Empirical Formula: Simplest ratio of elements; determined from percent composition.

• Molecular Formula: Actual number of atoms; may be a multiple of the empirical formula.

Solution Concentration: Molarity

Molarity (M) is the concentration of a solution, defined as moles of solute per liter of solution.

• Formula:

• To dilute a solution:

Electrolytes and Solution Types

Electrolytes are substances that conduct electricity when dissolved in water. Strong electrolytes dissociate completely; weak electrolytes partially dissociate; non-electrolytes do not dissociate.

• Strong Electrolytes: NaCl, HCl

• Weak Electrolytes: Acetic acid (CHCOOH)

• Non-electrolytes: Sugar, ethanol

Stoichiometry with Solutions

Stoichiometric calculations can use molarity to relate volumes and moles in reactions involving solutions.

• Convert volume to moles using molarity.

• Use balanced equations to relate moles of reactants and products.

Percent Yield

Percent yield compares the actual yield to the theoretical yield in a chemical reaction.

• Formula:

Additional info:

• Some context and explanations have been expanded for clarity and completeness.

• Tables have been reconstructed to summarize key conversions and ions.