Matter, Atoms, and Measurement

What is Chemistry?

Chemistry is the scientific study of matter, its composition, structure, properties, and the changes it undergoes during chemical reactions and physical processes.

• Matter: Anything that has mass and occupies space.

• Properties: Characteristics used to describe matter (e.g., color, density, boiling point).

• Chemical Change: Transformation resulting in new substances.

Classification of Matter

Matter can be classified based on its composition and uniformity.

• Pure Substances: Elements (e.g., Fe, O) and compounds (e.g., NaCl).

• Mixtures: Physical combinations of substances.

  • Homogeneous Mixtures: Uniform composition (e.g., saltwater).

  • Heterogeneous Mixtures: Non-uniform composition (e.g., sand and water).

Measurement in Chemistry

Accurate measurement is essential for scientific analysis and experimentation.

• Common Units: Mass (kilogram), length (meter), time (second), temperature (Kelvin, Celsius), amount (mole).

• Significant Figures: Indicate precision in measurements; zeros between non-zero digits are significant.

• Scientific Notation: Used for expressing very large or small numbers.

Density & Calculations

Density is a physical property that relates mass and volume.

• Density Formula:

• Units: g/cm3 or g/mL

• Conversion factors are essential for unit analysis.

Atomic Theory, Elements, and the Periodic Table

Atomic Structure

Atoms are the fundamental units of matter, composed of subatomic particles.

• Protons: Positive charge, found in nucleus.

• Neutrons: Neutral charge, found in nucleus.

• Electrons: Negative charge, found in electron cloud.

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons.

• Example: Carbon-12 vs. Carbon-14

The Periodic Table

The periodic table organizes elements by increasing atomic number and recurring chemical properties.

• Groups: Columns (alkali metals, alkaline earth metals, noble gases, etc.)

• Periods: Rows

Chemical Symbols & Formulas

Chemical symbols represent elements; formulas represent compounds.

• Elements: H, O, Fe, Cl, etc.

• Compounds: H2O, CO2, NaCl

Chemical Bonding, Molecules, and Compounds

Ionic vs. Covalent Bonding

Chemical bonds hold atoms together in compounds.

• Ionic Bonds: Transfer of electrons between metals and nonmetals (e.g., Na+ + Cl- → NaCl).

• Covalent Bonds: Sharing of electrons between nonmetals (e.g., H2O, CO2).

Molecules and Formula Units

Molecules are groups of atoms held together by covalent bonds; formula units refer to the simplest ratio of ions in ionic compounds.

Naming Compounds

• Ionic Compounds: Name cation first, use Roman numerals for transition metals.

• Covalent Compounds: Use prefixes (mono-, di-, tri-).

The Mole & Avogadro's Number

The mole is a counting unit for atoms, molecules, or ions.

• Avogadro's Number: particles per mole.

Percent Composition

Percent composition expresses the mass percentage of each element in a compound.

• Formula:

Chemical Reactions and Stoichiometry

Types of Chemical Reactions

Chemical reactions can be classified by the changes in reactants and products.

• Synthesis

• Decomposition

• Single Replacement

• Double Replacement

• Combustion

Balancing Chemical Equations

Balanced equations have equal numbers of each atom on both sides.

• Use coefficients to balance reactants and products.

Stoichiometry

Stoichiometry involves quantitative relationships in chemical reactions.

• Use balanced equations to predict amounts of reactants and products.

Limiting Reactant & Yield

• Limiting Reactant: The reactant that is completely consumed first, limiting the amount of product formed.

• Theoretical Yield: Maximum amount of product possible.

• Actual Yield: Amount measured in lab.

States of Matter, Solutions, Acids & Bases

States of Matter

Matter exists in different physical states: solid, liquid, gas.

• Solid: Definite shape and volume.

• Liquid: Definite volume, shape of container.

• Gas: Neither definite shape nor volume.

• Phase Changes: Melting, boiling, condensation, freezing, sublimation.

Gases

Gases are described by pressure, volume, temperature, and amount.

• Ideal Gas Law:

• P = pressure, V = volume, n = moles, R = gas constant, T = temperature.

• Units: atm, L, mol, K.

Solutions & Concentrations

Solutions are homogeneous mixtures of solute dissolved in solvent.

• Molarity (M):

Acids, Bases, and pH

Acids and bases are important classes of compounds with characteristic properties.

• Acids: Produce H+ ions in water (e.g., HCl).

• Bases: Produce OH- ions in water (e.g., NaOH).

• pH Scale: Measures acidity (pH < 7) or basicity (pH > 7);

• Neutralization: Acid + base → salt + water.

Safety and Applications

Safe laboratory practices are essential in chemistry. Chemistry is applied in food, medicine, environment, and materials science.

• Always follow proper lab safety precautions.

• Chemistry in everyday life: food, medicine, environment, materials.