GOB Chemistry Study Guide: Measurement, Matter, Atomic Structure, and Chemical Bonding

Chapter 1: Introduction and Measurement

Definition of Chemistry and Matter

Chemistry is the scientific study of matter, its properties, composition, and the changes it undergoes. Matter is anything that has mass and occupies space.

• Identify chemicals and matter: Recognize substances and their physical forms.

Significant Figures and Scientific Notation

• Significant Figures: Digits in a measurement that are known with certainty plus one estimated digit.

• Rules for Significant Figures:

  • All nonzero digits are significant.

  • Zeros between nonzero digits are significant.

  • Leading zeros are not significant.

  • Trailing zeros are significant only if there is a decimal point.

• Calculations with Significant Figures:

  • Multiplication/Division: The result should have as many significant figures as the measurement with the fewest significant figures.

  • Addition/Subtraction: The result should have as many decimal places as the measurement with the fewest decimal places.

• Scientific Notation: Expresses numbers as a product of a coefficient and a power of ten.

  • Example: $0.015$ is written as $1.5 \times 10^{-2}$

  • Example: $15,000$ is written as $1.5 \times 10^{4}$

Chapter 2: Chemistry and Measurements

Units of Measurement

Measurements in chemistry require standard units for mass, length, volume, time, and temperature.

• Identify standards and units of measurement:

  • Metric system prefixes: Mega (M), kilo (k), centi (c), milli (m), micro (μ), nano (n), etc.

• Unit Conversions: Use conversion factors to change from one unit to another (e.g., meters to centimeters, liters to milliliters).

• Percentages: Used as conversion factors in calculations.

Density

Density is a physical property defined as mass per unit volume.

• Formula: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

• Applications:

  • Calculate density from mass and volume.

  • Determine mass from density and volume.

  • Determine volume from density and mass.

Chapter 3: Matter and Energy

States of Matter

Matter exists in three primary states: solid, liquid, and gas. Each state has characteristic properties based on the arrangement and movement of particles.

• Solid: Definite shape and volume.

• Liquid: Definite volume, takes the shape of its container.

• Gas: No definite shape or volume, fills the container.

Classification of Matter

• Pure Substances: Elements and compounds with uniform composition.

• Mixtures: Physical combinations of two or more substances.

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

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

Chemical and Physical Properties and Changes

• Physical Properties: Observed without changing the substance (e.g., melting point, density).

• Chemical Properties: Describe how a substance reacts (e.g., flammability).

• Physical Change: Does not alter the chemical composition (e.g., melting ice).

• Chemical Change: Alters the chemical composition (e.g., rusting iron).

Energy in Chemistry

• Calorie (cal) and Joule (J): Units of energy.

  • $1 \text{ cal} = 4.184 \text{ J}$

• Kinetic Energy: Energy of motion.

• Potential Energy: Stored energy due to position or composition.

• Food Energy: Measured in kilocalories (kcal); different food types have different energy values.

Chapter 4: Atoms and Elements

Atomic Structure

Atoms are the basic units of matter, composed of protons, neutrons, and electrons.

• Atomic Number (Z): Number of protons in the nucleus.

• Mass Number (A): Total number of protons and neutrons.

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

• Number of Electrons: Equal to the number of protons in a neutral atom.

Isotopes

• Definition: Atoms of the same element with different numbers of neutrons.

• Isotopic Abundance: The relative amount of each isotope in a natural sample.

The Periodic Table

• Periodic Law: The properties of elements are periodic functions of their atomic numbers.

• Organization:

  • Periods: Horizontal rows

  • Groups: Vertical columns

• Element Categories: Metals, nonmetals, metalloids, noble gases.

• Trends: Atomic size, metallic character, ionization energy.

Ions and Valence Electrons

• Ions: Atoms or molecules that have gained or lost electrons.

• Cations: Positively charged ions (loss of electrons).

• Anions: Negatively charged ions (gain of electrons).

• Valence Electrons: Electrons in the outermost shell; determine chemical reactivity.

• Determining Valence Electrons: Number of Valence Electrons = Group Number (for main group elements)

• Octet Rule: Atoms tend to gain, lose, or share electrons to achieve eight valence electrons.

Chapter 6: Ionic and Molecular Compounds

Lewis Symbols and Ionic Bonding

• Lewis Symbols: Represent valence electrons as dots around the element symbol.

• Ionic Bonds: Formed by the transfer of electrons from metals to nonmetals, resulting in cations and anions.

• Writing Ionic Compounds: Combine cations and anions in ratios that yield a neutral compound.

Covalent Bonding and Molecular Compounds

• Covalent Bonds: Formed by sharing electrons between nonmetals.

• Lewis Structures: Show how atoms share electrons in molecules.

• Naming Compounds: Use prefixes for molecular compounds; name cation first for ionic compounds.

• Polyatomic Ions: Charged groups of covalently bonded atoms (e.g., $\text{NO}_3^-$, $\text{SO}_4^{2-}$).

Electrolytes and Nonelectrolytes

• Electrolytes: Substances that conduct electricity when dissolved in water (e.g., ionic compounds).

• Nonelectrolytes: Substances that do not conduct electricity in solution (e.g., most molecular compounds).

Sample Table: Classification of Matter

Type	Definition	Example
Element	Pure substance of one type of atom	Oxygen (O2)
Compound	Pure substance of two or more elements chemically combined	Water (H2O)
Homogeneous Mixture	Uniform composition throughout	Saltwater
Heterogeneous Mixture	Non-uniform composition	Salad