Category
Description
Example
Element
Pure substance made of one kind of atom
Oxygen (O■), Iron (Fe)
Compound
Pure substance made of 2+ elements chemically combined
Water (H■O), CO■
Mixture – Homogeneous
Uniform composition (solution)
Saltwater, Air
Mixture – Heterogeneous
Non-uniform composition
Salad, Soil
Example Problem: % by Mass Formula
% by mass = (mass of element ÷ mass of compound) × 100
If a 20 g sample of water (H■O) contains 2.22 g of hydrogen, what is the percent by mass of hydrogen
in water?
Solution:
% by mass = (2.22 g ÷ 20 g) × 100 = 11.1%
Therefore, hydrogen makes up 11.1% of the mass of water.
Chemistry Notes
What is Matter?
Matter: Anything that has mass and takes up space.
What is Chemistry?
Chemistry: The study of matter and the changes it undergoes.
Areas of Study in Chemistry
• Organic Chemistry – study of carbon-containing compounds.
• Inorganic Chemistry – study of compounds without carbon (minerals, metals).
• Analytical Chemistry – study of the composition of substances.
• Biochemistry – study of chemical processes in living organisms.
• Physical Chemistry – study of energy changes and properties of matter.
Pure vs. Applied Chemistry
• Pure Chemistry: Research for knowledge itself.
• Applied Chemistry: Research for practical goals (medicine, engineering).
Scientific Method (Steps)
1. Observe – make observations.
2. Hypothesis – propose an explanation.
3. Experiment – test the hypothesis.
4. Collect Data – record results.
5. Analyze – interpret data.
6. Conclude – accept or reject the hypothesis.
Accuracy vs. Precision
• Accuracy: closeness to true value.
• Precision: closeness of repeated measurements.
Scientific Notation
Used to express very large or tiny numbers.
Examples:
1.2 × 10³
4.5 × 10■²
7.89 × 10■
Substances
Substance: Matter with uniform and unchanging composition (pure).
Includes elements and compounds.
Properties of Matter
• Physical Properties: observed without changing composition (e.g., color, density).
• Chemical Properties: describe ability to change composition (e.g., flammability).
Extensive vs. Intensive Properties
• Extensive: depend on amount (mass, volume).
• Intensive: do not depend on amount (density, boiling point).
States of Matter
• Solid – definite shape and volume.
• Liquid – definite volume, shape of container.
• Gas – no definite shape or volume.
Law of Conservation of Matter
Matter cannot be created or destroyed in a chemical reaction.
Mixtures
Mixture: Combination of two or more pure substances.
• Homogeneous (solution): uniform composition (salt water, air).
• Heterogeneous: non-uniform, visibly different parts (salad, sand & water).
Separation Methods: filtration, distillation, chromatography, evaporation, magnetism.