Matter, Atoms, and Measurement

1. What is Chemistry?

Chemistry is the scientific study of matter, its composition, structure, properties, and the changes it undergoes. Understanding chemistry is fundamental to many scientific disciplines and everyday life.

• Matter: Anything that has mass and occupies space.

• Composition: The types and amounts of substances that make up matter.

• Properties: Characteristics used to identify and distinguish substances.

• Chemical Change: A process where substances are transformed into new substances.

2. Classification of Matter

Matter can be classified based on its composition and properties.

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

• Mixtures: Physical combinations of substances. Can be homogeneous (uniform, e.g., saltwater) or heterogeneous (non-uniform, e.g., salad).

• Physical vs. Chemical Properties: Physical properties can be observed without changing the substance; chemical properties describe how a substance reacts.

3. Measurement in Chemistry

Accurate measurement is essential in chemistry for quantifying substances and reactions.

• 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.

4. Density & Calculations

Density is a physical property that relates mass and volume.

• Density Formula:

• Common units: g/mL, g/cm3

• Density helps identify substances and solve problems involving mass and volume.

Atomic Theory, Elements, and the Periodic Table

1. Atomic Structure

Atoms are the basic 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.

2. Isotopes

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

• Example: Carbon-12 vs. Carbon-14.

3. The Periodic Table

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

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

• Periods: Rows.

4. 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

1. 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).

2. 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.

3. Naming Compounds

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

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

4. The Mole & Avogadro's Number

The mole is a counting unit in chemistry, relating mass to number of particles.

• Avogadro's Number: particles (atoms, ions, or molecules) per mole.

• Molar Mass: Mass of 1 mole of a substance (g/mol).

5. Percent Composition

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

• Formula:

Chemical Reactions and Stoichiometry

1. Types of Chemical Reactions

Chemical reactions can be classified by how reactants change into products.

• Synthesis

• Decomposition

• Single Replacement

• Double Replacement

• Combustion

2. Balancing Chemical Equations

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

• Use coefficients to balance equations.

• Law of Conservation of Mass: Matter is neither created nor destroyed.

3. Stoichiometry

Stoichiometry involves calculations based on balanced chemical equations to determine the amounts of reactants and products.

• Use mole ratios from coefficients.

4. Limiting Reactant & Yield

The limiting reactant is the substance that is completely consumed first, limiting the amount of product formed.

• Theoretical Yield: Maximum amount of product possible.

• Actual Yield: Amount measured in lab.

• Percent Yield Formula:

States of Matter, Solutions, Acids & Bases

1. 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.

2. 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.

3. Solutions & Concentrations

Solutions are homogeneous mixtures of solute dissolved in solvent.

• Molarity (M): Moles of solute per liter of solution.

• Formula:

4. 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).

• pH Formula:

• Neutralization: Acid + base → salt + water.

5. Safety and Applications

Safe laboratory practices are essential in chemistry. Chemistry has many applications in food, medicine, environment, and materials.

• Always follow proper lab safety precautions.

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