Chemistry

Distinctions Between Chemical and Physical Changes

• Chemical Changes: Involves a transformation that alters the substance's composition, resulting in new substances.

  • Clues: Color change, temperature change, gas production, formation of a precipitate, or light emission.

• Physical Changes: Involves changes in the physical properties of a substance without affecting its chemical composition.

  • Examples include changes of state (like melting or freezing).

Tests for Gases

• Oxygen: Glowing splint test - a glowing splint reignites in oxygen.

• Carbon Dioxide: Limewater test - bubbling carbon dioxide through limewater turns it milky due to the formation of calcium carbonate.

• Hydrogen: Pop test - a lit match or splint pops when placed in a test tube with hydrogen.

Chemical Families on the Periodic Table

• Alkali Metals: Group 1

• Alkaline Earth Metals: Group 2

• Transition Metals: Groups 3-12

• Halogens: Group 17

• Noble Gases: Group 18

Diatomic Molecules

• Definition: Molecules composed of only two atoms, which may be of the same or different chemical elements.

• List of Diatomic Molecules: H₂, N₂, O₂, F₂, Cl₂, Br₂, I₂.

Ions and Ionic Charges

• Ion Definition: An atom or molecule that has a net electrical charge due to the loss or gain of one or more electrons.

• Ionic Charges for Groups in the Periodic Table:

  • Group 1: +1

  • Group 2: +2

  • Group 13: +3

  • Group 15: -3

  • Group 16: -2

  • Group 17: -1

Ionic vs. Molecular Compounds

• Ionic Compounds: Formed from the electrostatic attraction between oppositely charged ions. Generally have high melting points and conduct electricity in solution.

• Molecular Compounds: Formed by covalent bonds between atoms. Generally lower melting points and do not conduct electricity.

Polyatomic Ions and Oxyacids

• Polyatomic Ions: Ions composed of two or more atoms bonded together, which carry a charge.

• Oxyacids: Acids that contain oxygen, typically formed from the reaction of water with an oxide of a nonmetal.

Law of Conservation of Mass

• States that in a closed system, mass is neither created nor destroyed in a chemical reaction.

Mass Calculation in Reactions

• For the reaction A + B → C + D:

  • Given: A = 12g, B = 15g, C = 9g.

  • Mass of D = (mass of A + mass of B) - mass of C = (12g + 15g) - 9g = 18g.

Chemical Equations

• Word Equations: Describes the reactants and products in words.

• Chemical Equations: Uses chemical formulas to represent the reactants and products.

• Balanced Equations: Equal number of atoms of each element on both sides of the equation.

Types of Chemical Reactions

1. Synthesis: Two or more substances combine to form a new compound.

2. Decomposition: A single compound breaks down into two or more simpler products.

3. Single Replacement: An element replaces another in a compound.

4. Double Replacement: Ions exchange between two compounds.

5. Combustion: A substance combines with oxygen, releasing energy in the form of light or heat.

• Clues for each type can include changes in color, temperature, gas release, or formation of solids.

Acids and Bases

• Properties of Acids: Sour taste, pH < 7, react with metals to produce hydrogen gas, turn blue litmus red.

• Properties of Bases: Bitter taste, slippery feel, pH > 7, turn red litmus blue.

• Distinguishing: Use of litmus paper or pH indicators.

• Formation: Acids form from hydrogen ions and bases from hydroxide ions.

pH Scale

• Ranges from 0 to 14. Acids are found < 7, neutral at 7, and bases > 7.

Neutralization Reaction

• Definition: A chemical reaction between an acid and a base that results in the formation of water and a salt.

• Reactants: Acid and base.

• Products: Water and a salt.