Classification of Matter

Types of Matter

Chemistry is the study of matter and the changes it undergoes. Matter is anything that occupies space and has mass. Matter can be classified into three main types:

• Element: The simplest type of matter, composed of one kind of atom. Example: Gold (Au).

• Compound: Matter composed of two or more different elements that are chemically bonded together. Example: Water (H2O).

• Mixture: Matter composed of elements and/or compounds that are physically mixed together. Example: Air, salsa.

Mixtures can be further classified as homogeneous (uniform composition, e.g., saline solution) or heterogeneous (variable composition, e.g., trail mix).

Practice Examples

• Compounds can only be broken down by chemical means.

• Milk is an example of a homogeneous mixture.

• Gold bar: Element; Ammonia (NH3): Compound; Orange juice: Mixture.

Physical and Chemical Changes

Physical Changes

Physical changes alter the physical state of a substance without changing its composition. Examples include melting, boiling, dissolving, and tearing.

• Example: Dissolving sugar in water is a physical change.

Chemical Changes

Chemical changes involve changes in chemical composition, resulting in new substances and chemical bonds. Examples include burning, rusting, and cooking.

• Example: Cooking an egg is a chemical change.

Reversible vs. Irreversible Changes

• Reversible Change: Can be undone to restore the original structure (e.g., phase changes, dissolving).

• Irreversible Change: Permanent and cannot be undone (e.g., most chemical changes).

Chemical Properties

Definition and Examples

Chemical properties are observed during a chemical reaction and result in the formation of new substances. Examples include flammability, reactivity, and toxicity.

• Example: Hydrogen gas reacts explosively with oxygen gas.

Physical Properties

Definition and Examples

Physical properties are measurable and describe the state of a chemical compound. They can be observed without changing the chemical structure. Examples include color, density, melting point, and luster.

• Example: Mercury is a silvery liquid at 25ºC.

Intensive vs. Extensive Properties

Intensive Properties

Intensive properties do not depend on the size or amount of substance present. Examples include density, temperature, melting point, and luster.

• Example: The melting point of a substance is intensive.

Extensive Properties

Extensive properties depend on the size or amount of substance present. Examples include mass, volume, and length.

• Example: The mass of a sample is extensive.

Temperature and Heat

Definitions

• Temperature: The average kinetic energy of an object.

• Heat: The flow of thermal energy from an object at a higher temperature to one at a lower temperature.

Temperature Conversions

• Temperature can be measured in degrees Celsius (ºC), Fahrenheit (ºF), and Kelvin (K).

• Conversion formulas:

Scientific Notation

Format and Conversion

Scientific notation is used to express very large or small numbers in a manageable form. The format is:

• Coefficient: A value ≥ 1 but < 10

• Base: Always 10

• Exponent: Indicates the number of decimal places moved

Conversion formulas:

• Standard to scientific: Move decimal to create coefficient between 1 and 10.

• Scientific to standard: Positive exponent makes value larger; negative exponent makes value smaller.

SI Units and Metric Prefixes

SI Base Units

The International System of Units (SI) is based on seven base units:

Metric Prefixes

Metric prefixes are modifiers that are multiples of ten and act as labels for base units. Examples include kilo (103), centi (10-2), milli (10-3), micro (10-6), nano (10-9).

Significant Figures

Rules and Precision

Significant figures are the digits that contribute to the precision of a value. The more significant figures, the more precise the measurement.

• Non-zero digits are always significant.

• Zeros between significant digits are significant.

• Leading zeros are not significant.

• Trailing zeros in the decimal portion are significant.

• Exact numbers have an infinite number of significant figures.

Significant Figures in Calculations

• Multiplication/Division: Final answer contains the least number of significant figures from the input values.

• Addition/Subtraction: Final answer contains the least number of decimal places from the input values.

• Mixed operations: Follow the order of operations (PEMDAS).

Conversion Factors and Dimensional Analysis

Conversion Factors

A conversion factor is a ratio or fraction that ties together two different units. Common conversion factors involve length, volume, and mass.

• Example: 1 inch = 2.54 cm

• Example: 1 kg = 2.2046 lbs

Dimensional Analysis

Dimensional analysis is a systematic process for converting from one unit to another using conversion factors. The process involves starting with the given amount, identifying the end amount, writing down all conversion factors, and canceling unwanted units.

Density

Definition and Formula

Density represents the amount of mass per unit of volume. For solids and liquids, units are typically g/cm3 or kg/L. For gases, units are g/L or kg/m3.

• Formula:

Density of Geometric Objects

For geometric objects, density can be related to mass and volume using formulas for cubes, spheres, and cylinders.

• Cube:

• Sphere:

• Cylinder:

Density of Non-Geometric Objects: Water Displacement

Water displacement is used to determine the volume of irregularly shaped objects by measuring the change in water level when the object is submerged.

Summary Table: SI Base Units

Additional info: Academic context and examples were added to ensure completeness and clarity for exam preparation.