CHE 205 General Chemistry Notes
Instructor Information
Instructor: Dr. Jolly Jacob, M.Sc., M.Phil., Ph.D., FICCE.
Position: Professor of Chemistry, Chair, Department of Applied Sciences, College of Applied Sciences (CAS). Dr. Jacob has extensive experience in research and teaching, focusing on various chemistry disciplines.
Chapter 1 - Introduction
1-1 The Scientific Method
The scientific method is a systematic approach utilized in research, allowing scientists to investigate phenomena, acquire new knowledge, or correct and integrate previous knowledge.
Steps in the scientific method include:
Observation: Gathering data to identify a phenomenon.
Hypothesis: A tentative explanation for a set of observations that is tested and modified based on experimental results.
Experimentation: Conducting tests to validate or falsify the hypothesis.
Conclusion: Analyzing data to determine whether to accept or reject the hypothesis.
Laws: Summaries of observations that condense multiple past observations into a general statement. For example:
Law of Conservation of Mass: “In a chemical reaction, matter is neither created nor destroyed,” which implies that the mass of reactants equals the mass of products.
1-2 Properties of Matter
Matter: Anything that occupies space and has mass, including gases, liquids, and solids.
Substance: A form of matter with a definite composition and distinct properties that can be identified through observation and measurement. Examples include pure water, sugar, and metals.
Everyday examples of matter include liquid nitrogen, gold ingots, and silicon crystals, all of which exhibit unique physical and chemical properties.
1-3 Classification of Matter
Atoms and Molecules:
Atoms are exceedingly small particles that make up all matter and consist of protons, neutrons, and electrons.
Molecules consist of two or more atoms bonded together by chemical bonds, which can either be covalent or ionic. An example is water (H₂O), which is composed of two hydrogen atoms and one oxygen atom.
Mixtures: Composed of two or more substances where each substance retains its distinct identity.
Homogeneous Mixtures: Consistent composition throughout, also known as solutions (e.g., air, seawater), where the components cannot be easily distinguished.
Heterogeneous Mixtures: Varied composition; for example, sand mixed with iron filings, where individual components remain separate and identifiable.
1-4 Measurement of Matter: SI (Metric) Units
Base Quantities:
Length: meter (m), which is defined by the distance light travels in a vacuum during a specific time.
Mass: kilogram (kg), a measure of the amount of matter in an object.
Time: second (s), the base unit of time; defined based on atomic clock accuracy.
Electrical current: ampere (A), representing the flow of electric charge.
Temperature: kelvin (K), a measure of thermal energy, where 0 K represents absolute zero.
Amount of substance: mole (mol), which quantifies entities such as atoms or molecules.
Luminous intensity: candela (cd), measuring the perceived power of light.
Derived Units:
Volume: , indicating the space occupied by a substance.
1-5 Density and its Use in Problem Solving
Density is defined as:
, where $d$ is the density, $m$ is mass, and $V$ is volume.
The SI derived unit for density is (kilograms per cubic meter).
Examples of density calculations:
A platinum metal sample with a density of and volume results in a mass of:
, demonstrating how density can be used to calculate mass based on known volume.
1-6 Uncertainties in Scientific Measurements
Emphasis on the importance of significant figures in measurements, as they reflect the precision of measurements and calculations.
Precision: Refers to the consistency between repeated measurements, while Accuracy: indicates how close a measurement is to the true value. Understanding both concepts is essential for experimental validity.
1-7 Significant Figures
Any non-zero digit is significant due to its contribution to the overall measurement.
Zeros between non-zero digits are significant as they provide essential value information.
Leading zeros, which appear before the first non-zero digit, are not considered significant.
For numbers greater than 1, all zeros to the right of the decimal point are significant, indicating precision. For numbers less than 1, only zeros at the end and between significant digits are deemed significant, helping to clarify measurement accuracy.
Types of Changes
Physical Change: Does not alter the composition or identity of a substance (e.g., ice melting, sugar dissolving in water), showcasing changes that affect form, not chemical identity.
Chemical Change: Alters the composition or identity of the substances involved (e.g., hydrogen burning in air to form water), indicating a transformation that creates new substances with different properties.
Physical vs. Chemical Properties
Physical Properties: Observed without changing the substance, such as:
Color
Mass
Weight
Boiling point
Melting point
Chemical Properties: Can only be studied through the formation of new substances, reflecting how a substance reacts under specific conditions (e.g., reactivity with acids, flammability).
Further Classifications of Matter
Elements: Cannot be separated into simpler substances by chemical means. There are 118 identified elements; 82 occur naturally on Earth (e.g., gold, aluminum), and each element is defined by its atomic number and specific properties.
Compounds: Composed of atoms from two or more elements chemically united in fixed proportions (e.g., lithium fluoride, quartz), illustrating how chemical bonds unite different elements to form new materials with unique characteristics.
Special Mention: Nanoworld
Nanotechnology: The study of manipulating matter at the atomic or molecular level, unlocking potential applications in fields such as medicine, electronics, and materials science, emphasizing its transformative role in various innovative technologies.