Chemistry Basics Quiz

Essential Notes on Chemistry

• Matter: Composed of small particles called atoms and molecules. Different atoms and molecules exhibit different properties.

Laws of Chemical Combination

• Law of Conservation of Mass: Mass cannot be created or destroyed during a chemical reaction. The total mass of the reactants equals the total mass of the products.

• Antoine Lavoisier (1774)

• Example: Calcium Carbonate (CaCO3) decomposing into Calcium Oxide (CaO) and Carbon Dioxide (CO2); 100g CaCO3 decomposes to 56g CaO + 44g CO2

• Law of Constant Proportion: A chemical compound always contains the same elements in a fixed ratio by mass.

• Joseph Proust (1779)

• Example: Water (H₂O) always contains hydrogen and oxygen in a 1:8 ratio by mass

Dalton's Atomic Theory

• All matter is composed of tiny, indivisible particles called atoms.
• Atoms of the same element are identical in shape, size, mass, and chemical properties.
• Atoms of different elements have different sizes, shapes, masses, and chemical properties.
• Atoms combine in simple whole number ratios to form chemical compounds
• Atoms are neither created nor destroyed in a chemical reaction.

Limitations of Dalton's Atomic theory

• Atoms can be further divided into subatomic particles.
• Atoms of the same element can have slightly different masses.
• Atoms of different elements can have similar masses.

Molecules

• Molecule: A group of two or more atoms held together by chemical bonds.
• Monatomic: Molecules composed of a single atom (e.g., noble gases).
• Diatomic: Molecules composed of two atoms (e.g., H₂).
• Triatomic: Molecules composed of three atoms (e.g., O₃).
• Polyatomic: Molecules composed of more than three atoms (e.g., H₂O).

Atomicity

• Atomicity of an element is the number of atoms present in one molecule of the element.
• Noble gases (monatomic(e.g., Helium, Argon),
• Metals (e.g., sodium) and nonmetals (e.g., carbon), may exist as polyatomic molecules

Ions

• Cations: Positively charged ions formed by losing electrons.
• Anions: Negatively charged ions formed by gaining electrons.
• Valency: The combining capacity of an element, determined by the number of electrons lost or gained.

Polyatomic Ions

• Polyatomic Ions: Groups of atoms carrying a positive or negative charge.
• Examples includes: Ammonium (NH₄⁺), Nitrate (NO₃⁻), Sulfate (SO₄²⁻), etc.

Atomic Symbols and Formulas

• Chemical symbols (e.g., H for hydrogen, O for oxygen).
• Chemical formulas (e.g., H₂O for water, CO₂ for carbon dioxide).