Classification of Matter and SI Units: Introduction to Chemistry Study Notes

Classification of Matter

Pure Substances vs. Mixtures

In chemistry, all matter can be classified as either a pure substance or a mixture. Understanding the differences between these categories is fundamental to the study of chemical properties and reactions.

• Pure Substance: A material with a constant composition and distinct chemical properties. Pure substances can be either elements or compounds.

• Mixture: A physical blend of two or more substances, where each retains its own identity and properties. The composition of a mixture can vary.

Key Points:

• Elements: Substances made of only one type of atom. Examples: Oxygen (O2), Gold (Au).

• Compounds: Substances composed of two or more elements chemically bonded in fixed proportions. Example: Water (H2O).

• Mixtures: Can be separated by physical means (e.g., filtration, distillation) because their components are not chemically bonded.

Example: Water (H2O) is a pure substance; air is a mixture of gases.

Types of Mixtures

Mixtures are further classified based on their uniformity and composition.

• Homogeneous Mixtures (Solutions): Mixtures that are uniform throughout, with the same proportions of components everywhere. Examples include salt water, air, and alloys.

• Heterogeneous Mixtures: Mixtures that are not uniform; different parts have different compositions. Examples include chocolate chip cookies, salads, and concrete.

Examples of Homogeneous Mixtures:

• Gas in Gas: Oxygen in nitrogen (air)

• Gas in Liquid: Carbon dioxide in water (soda)

• Liquid in Liquid: Alcohol in water

• Liquid in Solid: Mercury in silver and tin (silver dental fillings)

• Solid in Liquid: Sugar in water (Kool-Aid)

• Solid in Solid: Alloys like 14K gold, brass

Examples of Heterogeneous Mixtures:

• Chocolate chip cookies

• Salad

• Concrete

• Sedimentary rocks

• Milk (even though it appears uniform, it is technically heterogeneous)

Properties of Pure Substances

Pure substances have consistent properties and composition.

• Characteristic Properties: Every sample of a pure substance has the same properties. For example, pure water freezes at 0°C and boils at 100°C.

• Constant Composition: The ratio of elements in a compound is always the same. For water, the composition is 88.8% oxygen and 11.2% hydrogen by mass.

Example: The chemical formula for water is $H_2O$.

SI Base Units (International System of Units)

Overview of SI Units

The International System of Units (SI) provides standard units for scientific measurements, ensuring consistency and accuracy in experiments and data comparison.

Quantity	Quantity Symbol	SI Base Unit	SI Unit Symbol
Length	l	meter	m
Mass	m	kilogram	kg
Time	t	second	s
Temperature	T	kelvin	K
Amount of Substance	n	mole	mol
Electric Current	I	ampere	A
Luminous Intensity	Iv	candela	cd

Key Points:

• SI units are used worldwide for scientific measurements.

• Using standard units allows for accurate comparison of experimental data.

Example: The temperature of water boiling is measured in kelvin ($K$) or degrees Celsius (°C).

Additional info: Some entries in the original table were inferred for completeness and clarity.