Basic Chemistry Concepts Explained

Classifying Matter

• Pure Substance: Element or compound.
• Mixture: Homogeneous (uniform) or heterogeneous (non-uniform).
• Element: One type of atom.
• Compound: Two or more atoms chemically bonded.

Properties of Matter

• Physical: Observable without changing the substance (e.g., color, density).
• Chemical: Describes the potential for a substance to change (e.g., reactivity).
• Physical Change: No new substance is formed (e.g., melting).
• Chemical Change: A new substance is formed (e.g., burning).

Atomic Structure

Protons, Neutrons, Electrons (PEN)

• Protons: Positive charge (+1), located in the nucleus.
• Neutrons: No charge (0), located in the nucleus.
• Electrons: Negative charge (-1), located in shells around the nucleus.
• PEN Relationships:
  • Protons = Atomic number.
  • Neutrons = Atomic mass - atomic number.
  • Electrons = Same as protons in neutral atoms.

Valence Shell & Diagrams

• Valence Shell: The outermost electron shell, involved in bonding.
• Bohr-Rutherford Diagrams: Show the arrangement of electrons in shells.

Ions

• Cation: A positive ion (formed by losing electrons).
• Anion: A negative ion (formed by gaining electrons).
• Ion Diagrams: Adjust the number of electrons to reflect the charge.

Representing Molecules

• Lewis Dot Diagrams: Show valence electrons and bonding (e.g., NaCl).

Naming & Formula Writing

1. Ionic Compounds: Metal + non-metal (e.g., NaCl - Sodium chloride).
2. Multivalent Compounds: Use Roman numerals for the metal's charge (e.g., FeCl₃ - Iron(III) chloride).
3. Polyatomic Compounds: Contain polyatomic ions (e.g., Na₂SO₄ - Sodium sulfate).
4. Molecular Compounds: Non-metal + non-metal (e.g., CO₂ - Carbon dioxide).
5. Acids: Binary (e.g., HCl - Hydrochloric acid) or oxyacids (e.g., H₂SO₄ - Sulfuric acid).

Chemical Bonding

• Ionic Bond: Electrons are transferred between atoms (e.g., NaCl).
• Covalent Bond: Electrons are shared between atoms (e.g., H₂O).
• Ionic Compounds: Typically have high melting/boiling points and conduct electricity when molten or dissolved.
• Covalent Compounds: Typically have low melting/boiling points and do not conduct electricity.

Chemical Reactions

Reactants and Products

• Reactants: Substances that undergo a change in a reaction.
• Products: New substances formed as a result of a reaction.
• Counting Atoms: Use subscripts in formulas (e.g., H₂O has 2 Hydrogen atoms and 1 Oxygen atom).
• Law of Conservation of Mass: Mass is conserved in a chemical reaction; atoms are rearranged, not created or destroyed.

Chemical Equations

• Word Equation: Describes the reaction using the names of substances.
• Skeleton Equation: Shows the formulas of reactants and products, unbalanced.
• Balanced Equation: Has the same number of atoms of each element on both sides of the equation.

Types of Chemical Reactions

• Synthesis: A + B → AB.
• Decomposition: AB → A + B.
• Combustion: Typically Hydrocarbon + O₂ → CO₂ + H₂O.
• Single Displacement: AB + C → AC + B.
• Double Displacement: AB + CD → AD + CB.

Acids and Bases

Definitions and Properties

• Acid: Donates H⁺ ions (e.g., HCl).
• Base: Accepts H⁺ ions or donates OH⁻ ions (e.g., NaOH).
• Acids: Taste sour, have a pH < 7, turn blue litmus paper red.
• Bases: Taste bitter, feel slippery, have a pH > 7, turn red litmus paper blue.

pH Scale and Indicators

• pH Scale: Measures acidity/basicity. Acidic < 7, Neutral = 7, Basic > 7.
• Litmus Paper: An indicator; red in acids, blue in bases.
• Universal Indicator: A mixture of indicators showing a range of colors across the full pH scale.