CHEM 111-004 Chapter 1 (1-14-25)

Chapter 1: Introduction to Chemistry

1.1 The Nature of Science and Chemistry

• Objectives:

  • Define science and chemistry.

  • Describe the scientific method.

  • Compare and contrast hypothesis, law, and theory.

1.2 The Nature of Science

• Science is defined as knowledge, particularly that gained through experience or experiment (empirical knowledge). It encompasses both the activities associated with investigating the natural world and the knowledge resulting from those explorations.

• Chemistry specifically studies matter, focusing on its interactions with other forms of matter and energy.

The Scientific Method

• The scientific method involves investigations guided by theories and results from prior experiments. This method includes:

  • Hypothesis: A potential explanation for an event or observation.

  • Law: A concise statement summarizing a significant number of observations, usually recognizable through consistent results under specific conditions.

  • Theory: A broader explanation of natural laws that incorporates a wide range of observations.

1.3 Matter

• Objectives:

  • Define matter and its properties.

  • Distinguish between intensive and extensive properties.

  • Differentiate between chemical and physical properties and changes.

  • Classify matter based on its properties and composition.

  • Differentiate between elements and compounds.

Definition of Matter

• Matter is defined as anything that has mass and occupies space. Two critical aspects are:

  • Mass: The quantity of matter an object contains.

  • Weight: The gravitational force acting on that mass from other objects.

Properties of Matter

• Properties refer to any observable or measurable characteristics of matter:

  • Extensive Properties: Dependent on the size of the sample, such as mass and volume.

  • Intensive Properties: Independent of sample size, including density, color, melting point, and boiling point.

Physical Properties and Changes

• Physical Properties can be measured without altering the composition of the sample (e.g., mass, density, color, melting point).

• Physical Changes occur without changing the material's composition, such as freezing or melting.

Chemical Properties and Changes

• Chemical Properties describe how a material reacts with others (e.g., methane's combustion in air).

• Chemical Changes involve a transformation that results in the formation of a different substance, like the combustion of methane producing carbon dioxide and water.

Classification of Matter

• Matter is classified into two main categories: Substances and Mixtures.

  • Substances: Are homogeneous materials with consistent composition throughout. They can be further broken down into:

    • Elements: Cannot be decomposed into simpler substances (e.g., Al, As).

    • Compounds: Can be broken down into elements (e.g., NaCl, Glucose).

Mixtures

• Mixtures can be separated using physical methods:

  • Heterogeneous Mixtures: Have varying compositions in different parts (e.g., rock).

  • Homogeneous Mixtures (Solutions): Uniform composition throughout (e.g., air, alloys like brass).

1.4 Measurements and Uncertainty

• Objectives:

  • Differentiate between accuracy and precision.

  • Apply significant figures in expressing measurement uncertainty.

  • Report calculation results with the correct number of significant figures.

Accuracy and Precision

• Measurement confidence is based on:

  • Accuracy: Closeness of measured values to the true value.

  • Precision: Closeness of repeated measurements to each other.

Significant Figures

• Significant Figures illustrate the precision of measurements. Important rules include:

  1. All non-zero numbers are significant.

  2. Leading zeros are not significant.

  3. Captive zeros (between non-zero digits) are significant.

  4. Trailing zeros are significant only if there is a decimal.

Rounding Methods

• Rounding rules depend on the digit following the last significant figure:

  • Less than 5: round down.

  • Exactly 5: round to the nearest even number.

  • More than 5: round up.