Basic Chemistry and the Scientific Method

Basic Chemistry Concepts

• Chemistry is the study of substances in terms of their composition, structure, properties, and reactions.
• Chemicals are substances with consistent composition and properties.
• Examples include sugar, water, and salt.
• Light, heat, energy, sound, magnetism, and reflection are not considered chemicals.

The Scientific Approach to Knowledge

• Scientific knowledge is empirical, based on observation and experimentation.
• The scientific method is a process for understanding nature through observation and experimentation.
• Key characteristics of the scientific method include observations, hypothesis formulation, experimentation, and conclusion/theory formulation.

Scientific Method Steps

• Observation (noting and recording natural phenomena; AKA data)
• Hypothesis (a tentative explanation of facts, based on reasoning and evidence; often in an if-then statement; must be falsifiable)
• Experiment (a procedure to test the hypothesis)
• Theory/Conclusion (a well-established hypothesis or set of hypotheses that explains natural phenomena)
• Law (a brief statement summarizing past observations and predicting future ones)

Everyday Scientific Thinking

• Observations of everyday phenomena can be used to form hypotheses and test them through experiments.
• A hypothesis can be tested and validated or invalidated through experiments, leading to conclusions.

Scientific Measurement

• Qualifiable data are observational and subjective.
• Quantifiable data depend on numbers and units (empirical).
• Scientific instruments are utilized to gather empirical data with standardized units, these units being crucial.

Units of Measurement

• Units quantify measurements, important for 99.9% of numbers.
• SI (International System of Units) is a standardized metric system of measurement.
• Common SI units include meters (m) for length, liters (L) and milliliters (mL) for volume, kilograms (kg) for mass, seconds (s) for time, Celsius (°C) and Kelvin (K) for temperature etc.

Standard and Scientific Notation

• Scientific notation represents very large or very small numbers using a coefficient and a power of ten.
• The coefficient must be at least 1 but less than 10, the number of spaces moved to obtain the coefficient is shown as a power of ten.

Significant Figures

• Scientific measurements use significant figures (SF), including estimated digits, to convey accuracy.
• All non-zero digits are significant.
• Zeros may be significant depending on their position in the number or written in scientific notation.

Exact Numbers

• Exact numbers are obtained from counting discrete items or from defined relationships between units (e.g., 1 ft = 12 inches).
• Exact numbers do not limit the number of significant figures in calculations.

Conversion Factors

• Conversion factors relate different units that measure the same quantity.
• Conversion factors are often derived from equalities and used to change units in calculations.
• Conversion factors based on defined equalities do not affect the number of significant figures in an answer.
• Conversion factors based on measured quantities affect the number of significant figures.

Physical Properties

• Physical properties describe a substance without changing its chemical identity.
• Examples include color, shape, melting point, boiling point, and physical state.

Physical Changes

• Physical changes alter a substance's physical state or appearance, but not its chemical composition.
• Examples include boiling, freezing, dissolving, and cutting.

Chemical Properties

• Chemical properties indicate a substance's ability to interact with other substances and transform into a new substance.

Chemical Changes

• Chemical changes result in the formation of new substances with different chemical and physical properties.
• Examples include burning, rusting, and cooking.

Atomic Structure

• Atoms are the basic building blocks of matter, too small to be seen with the naked eye.
• Atoms are composed of subatomic particles: protons (positive charge), neutrons (no charge), and electrons (negative charge).
• Protons and neutrons are located in the nucleus of the atom and electrons orbit the nucleus.
• The mass of an atom is primarily determined by the masses of protons and neutrons.

Atomic Number

• The atomic number represents the number of protons in an atom and is characteristic of each element.
• The atomic number is used to identify the element and locate it on the periodic table.

Mass Numbers

• The mass number is the sum of protons and neutrons in an atom's nucleus.
• Mass number is used to determine the number of neutrons in a given isotope.

Isotopes

• Isotopes are atoms of the same element that have the same atomic number but different mass numbers (because different number of neutrons)

Atomic Mass

• The atomic mass of an element is a weighted average of the masses of its naturally occurring isotopes.
• Atomic mass values are listed below the element's symbol on the periodic table.

Density

• Density compares mass to volume.
• D = m/V (Density = mass/volume)
• Density is a physical property that can be used to identify substances.
• Different substances generally have different densities.
• The density of a solid or liquid is often expressed in g/cm3 or g/mL, while the density of a gas is often expressed in g/L.

More notes on Density

• The density of a substance depends on the closeness of packing of its particles.
• Higher densities usually result from particles packed closely together.
• Substances with lower density will have its particles further apart.