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

Chapter 1: Introduction to Chemistry and Measurement

Definition of Chemistry and Matter

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

• Chemicals: Substances with a definite composition.

• Matter: Anything that has mass and takes up space.

Significant Figures and Scientific Notation

Accurate measurement in chemistry requires understanding significant figures and scientific notation.

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

• Rules for Significant Figures:

  • Multiplication/Division: Result has the same number of significant figures as the measurement with the fewest significant figures.

  • Addition/Subtraction: Result has the same number of 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: $6.15 \times 10^1$

  • Standard notation: $1.5 \times 10^{-3} = 0.0015$

Chapter 2: Chemistry and Measurements

Units of Measurement

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

• SI Units: International System of Units used for scientific measurements.

• Metric Prefixes: Used to express multiples or fractions of units (e.g., kilo-, centi-, milli-).

• Conversion: Use conversion factors to change between units (e.g., meters to centimeters).

• 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 distinct properties based on particle arrangement and energy.

• Solids: Definite shape and volume; particles are closely packed.

• Liquids: Definite volume but no definite shape; particles are less tightly packed than solids.

• Gases: No definite shape or volume; particles are far apart and move freely.

Classification of Matter

Matter can be classified as pure substances or mixtures.

• Pure Substance: Element or compound with uniform composition.

• Mixture: Combination of two or more substances; can be homogeneous (uniform) or heterogeneous (non-uniform).

Chemical and Physical Properties and Changes

Properties and changes in matter are classified as physical or chemical.

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

• Chemical Properties: Characteristics observed during a chemical change (e.g., reactivity).

• Physical Change: Change in state or appearance without altering composition.

• Chemical Change: Change that produces new substances.

Energy in Chemistry

Energy is the capacity to do work or produce heat. It exists in various forms in chemical systems.

• Kinetic Energy: Energy due to motion.

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

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

  • 1 cal = 4.184 J

• Food Energy: Measured in Calories (Cal); 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): Sum of protons and neutrons.

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

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

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons.

• Definition: Atoms with the same atomic number but different mass numbers.

• Abundance: Natural abundance of isotopes affects average atomic mass.

The Periodic Table

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

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

• Rows (Periods): Horizontal; Columns (Groups): Vertical.

• Classification: Metals, nonmetals, metalloids.

• Special Groups: Alkali metals, alkaline earth metals, halogens, noble gases.

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

Chapter 5: Ions and Ionic Compounds

Ions and Electron Configuration

Ions are atoms or molecules with a net electric charge due to loss or gain of 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.

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

• Valence Electron Calculation: $\text{Number of Valence Electrons} = \text{Group Number}$

Chapter 6: Ionic and Molecular Compounds

Lewis Symbols and Ionic Bonding

Lewis symbols represent valence electrons and help visualize ionic and covalent bonding.

• Lewis Symbols: Dots around element symbols representing valence electrons.

• Ionic Bonds: Electrostatic attraction between cations and anions; electrons are transferred.

• Writing Ionic Compounds: Combine cations and anions to form neutral compounds.

Covalent Bonding and Molecular Compounds

Covalent bonds involve sharing of electrons between nonmetal atoms.

• Covalent Bonds: Shared pairs of electrons between atoms.

• Writing Formulas: Use element symbols and subscripts to indicate number of atoms.

• Polyatomic Ions: Ions composed of two or more atoms covalently bonded.

Electrolytes and Non-Electrolytes

Electrolytes conduct electricity in solution; non-electrolytes do not.

• Electrolytes: Substances that dissociate into ions in water.

• Non-Electrolytes: Substances that do not produce ions in solution.

Additional Table: Classification of Matter

The following table summarizes the classification of matter:

Type	Description	Examples
Element	Pure substance made of one type of atom	O2, Fe, Na
Compound	Pure substance made of two or more types of atoms chemically bonded	H2O, NaCl
Homogeneous Mixture	Uniform composition throughout	Salt water, air
Heterogeneous Mixture	Non-uniform composition	Sand and water, salad