General Chemistry Fundamentals: Concepts, Properties, and Atomic Structure

The Scientific Method

Overview

The scientific method is a systematic approach used in scientific investigation to acquire new knowledge and validate existing concepts. It involves making observations, forming hypotheses, conducting experiments, analyzing data, and drawing conclusions.

• Hypothesis: A testable statement or prediction about a phenomenon. Must be falsifiable, meaning it can be proven wrong through experimentation.

• Experiments: Procedures carried out to test the hypothesis under controlled conditions.

• Data Analysis: Evaluation and interpretation of experimental results.

• Drawing Conclusions: Determining whether the hypothesis is supported or refuted by the data.

Scientific Laws are statements based on repeated experimental observations that describe some aspect of the world. Scientific Theory is a well-substantiated explanation of some aspect of the natural world, based on a body of evidence.

States and Types of Matter

States of Matter

Matter exists in different physical forms, known as states of matter. Each state has distinct properties.

• Solid: Has a definite shape and volume.

  • Crystalline: Particles are arranged in a regular, repeating pattern (e.g., table salt).

  • Amorphous: Particles lack a long-range order (e.g., glass).

• Liquid: Has a definite volume but takes the shape of its container.

• Gas: Has neither definite shape nor volume; expands to fill its container.

Types of Matter

• Mixture: A combination of two or more substances where each retains its own properties.

  • Homogeneous: Uniform composition throughout (e.g., saltwater).

  • Heterogeneous: Non-uniform composition (e.g., salad).

• Pure Substance: Matter with a fixed composition; can be an element or a compound.

Properties and Changes of Matter

Properties

• Physical Properties: Characteristics observed without changing the substance's chemical identity (e.g., color, melting point).

  • Example: The melting point of ice is 0°C.

• Chemical Properties: Characteristics that become evident during or after a chemical change (e.g., reactivity with acid).

  • Example: Iron reacts with oxygen to form rust.

Changes

• Physical Changes: Alterations that do not change the chemical composition (e.g., phase changes).

  • Example: Boiling water changes it from liquid to gas.

• Chemical Changes: Alterations that change the chemical structure (e.g., combustion).

  • Example: Burning wood produces ash, carbon dioxide, and water.

Significant Figures and Scientific Notation

Significant Figures

Significant figures are the digits in a measurement that are known with certainty plus one estimated digit. They reflect the precision of a measurement.

• Zeroes:

  • Interior: Zeroes between nonzero digits are significant (e.g., 205).

  • Leading: Zeroes before the first nonzero digit are not significant (e.g., 0.0025).

  • Trailing: Zeroes after a decimal point and a nonzero digit are significant (e.g., 2.50).

• Scientific Notation: Used to express very large or small numbers. Example: $6.02 \times 10^{23}$.

• Rounding: When performing calculations, round the final answer to the correct number of significant figures based on the operation.

Unit Conversions

Cross-Multiplication Method

Unit conversions are performed using conversion factors and the cross-multiplication method to ensure correct dimensional analysis.

• Example: To convert 10 cm to meters: $10 \text{ cm} \times \frac{1 \text{ m}}{100 \text{ cm}} = 0.1 \text{ m}$

Laws of Proportions

Law of Definite Proportions

This law states that a chemical compound always contains the same proportion of elements by mass.

• Example: Water (H2O) always contains 2 parts hydrogen to 16 parts oxygen by mass.

Law of Multiple Proportions

If two elements form more than one compound, the masses of one element that combine with a fixed mass of the other are in ratios of small whole numbers.

• Example: CO and CO2 (carbon monoxide and carbon dioxide).

The Structure of the Atom

Atomic Structure

Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons.

• Protons: Positively charged particles in the nucleus.

• Neutrons: Neutral particles in the nucleus.

• Electrons: Negatively charged particles orbiting the nucleus.

Isotopes

Understanding Isotopes

Isotopes are atoms of the same element with different numbers of neutrons, resulting in different mass numbers.

• Number of Protons: Equal to the atomic number (Z).

• Number of Neutrons: $\text{Neutrons} = \text{Mass Number} - \text{Atomic Number}$

• Natural Abundance: The relative percentage of each isotope in a natural sample of the element.

Reading the Periodic Table

Groups and Charges

The periodic table organizes elements by increasing atomic number and groups elements with similar properties into columns called groups.

• Groups: Vertical columns; elements in the same group have similar chemical properties.

• Determining Ionic Charges: Main group elements often form ions with predictable charges (e.g., Group 1 forms +1 ions).

Ions

Types of Ions

• Cations: Positively charged ions (e.g., Na+).

• Anions: Negatively charged ions (e.g., Cl-).

• Polyatomic Ions: Ions composed of two or more atoms covalently bonded (e.g., SO42-).

• Determining Charge: Based on group number and electron loss/gain.

• Naming: Cations use the element name; anions often end in "-ide" or use specific names for polyatomic ions.

Formula Writing and Naming Compounds

Writing Formulas

Formulas represent the types and numbers of atoms in a compound. Naming follows specific rules based on the type of compound.

• Example: KI (Potassium iodide), Sr(NO3)2 (Strontium nitrate), CCl4 (Carbon tetrachloride), H2SO4 (Hydrogen sulfate), CuO (Copper(II) oxide), Co(NO3)2 (Cobalt(II) nitrate), CaCO3 (Calcium carbonate).

In-Class Math Review

• 3.5 - 2.396 = 1.104

• 2.341 × 376 × 0.007 = 6.159

• (7826 + 23 - 5.2) × 7.5 = 58799.0

• (5.95 × 3.7628) - 4.25 = 18.09966

Additional info:

• For formula writing, the subscripts indicate the number of each atom present in the compound.

• Polyatomic ions have specific names and charges that must be memorized for accurate formula writing.

• Significant figures in calculations depend on the precision of the measured values used.