Chemistry Exam 1 Study Guide: Matter, Atomic Structure, and Quantitative Chemistry

Fundamentals of Matter and Its Classification

• Matter: Anything that has mass and takes up (occupies) space.
• Mass: A measure of the amount of matter in an object; does not change with location.
• Physical Properties: Characteristics that can be observed or measured without changing the substance's chemical identity.
  • Examples include color, melting point, and density.
• Chemical Properties: Characteristics that describe how a substance reacts or changes into a different substance.
  • Examples include flammability and reactivity with acid.
• Physical Change: A change in a substance's form or state that does not alter its chemical identity.
  • Examples include melting ice and cutting paper.
• Chemical Change: A change that produces a new substance with a different chemical composition.
  • Examples include rusting and burning.
• Pure Substance: Matter with a fixed, uniform composition (encompasses elements and compounds).
  • Element: A pure substance that cannot be broken down into simpler substances by chemical means; made of only one type of atom.
  • Compound: A pure substance made of two or more elements chemically combined in a fixed ratio.
• Mixture: A physical combination of two or more substances that can be separated by physical means; composition can vary.
  • Homogeneous Matter: Matter with uniform composition and properties throughout (e.g., saltwater, air).
  • Heterogeneous Matter: Matter with non-uniform composition; distinct parts or phases can be seen (e.g., salad, sand and water).

Atoms, Molecules, and Molecular Classification

• Atoms: The smallest unit of an element that retains the properties of that element.
• Molecules: Two or more atoms chemically bonded together.
• Molecular Classification by Atom Count:
  • Diatomic Molecules: Molecules made of exactly two atoms (e.g., $O_2$, $HCl$).
  • Triatomic Molecules: Molecules made of exactly three atoms (e.g., $H_2O$, $CO_2$).
  • Polyatomic Molecules: Molecules made of more than two atoms.
• Molecular Classification by Element Composition:
  • Homoatomic Molecules: Molecules composed of only one type of element (e.g., $O_2$, $O_3$).
  • Heteroatomic Molecules: Molecules composed of two or more different elements (e.g., $H_2O$, $CO_2$).

Subatomic Particles and Atomic Structure

• Nucleus: The dense central core of an atom containing protons and neutrons.
• Subatomic Particles: The particles that make up an atom:
  • Proton: A positively charged subatomic particle found in the nucleus; mass \text{mass} \buildrel \text{ \text{\tilde}} \text{=} 1\,\text{amu}.
  • Neutron: A neutrally charged (no charge) subatomic particle found in the nucleus; mass \text{mass} \buildrel \text{ \text{\tilde}} \text{=} 1\,\text{amu}.
  • Electron: A negatively charged subatomic particle found outside the nucleus in electron shells; possesses negligible mass.
• Atomic Number: The number of protons in an atom's nucleus; defines the element.
• Atomic Mass Number: The total number of protons plus neutrons in an atom's nucleus.
• Atomic Weight: The weighted average mass of all naturally occurring isotopes of an element, as found on the periodic table.
• Atomic Mass Unit ($\text{amu}$ or $\text{u}$): A unit of mass used to express atomic and molecular masses; 1\,\text{amu} \buildrel \text{ \text{\tilde}} \text{=} \text{mass of one proton or neutron}.
• Isotope: Atoms of the same element (same number of protons) that have different numbers of neutrons, and therefore different mass numbers.
• Ion: An atom or molecule that has gained or lost electrons, giving it a net positive charge (cation) or negative charge (anion).
• Valence Electron / Shell: Electrons in the outermost energy shell of an atom; the shell that determines chemical bonding behavior.
• Ionization Energy: The energy required to remove an electron from a neutral atom in the gas phase.

Periodic Table Organization and Element Types

• Family or Group: A vertical column on the periodic table; elements in the same group have similar chemical properties and the same number of valence electrons.
• Period: A horizontal row on the periodic table; elements in the same period have the same number of electron shells.
• Metals: Elements that are typically shiny, malleable, ductile, and good conductors of heat and electricity; tend to lose electrons.
• Nonmetals: Elements that are typically dull, brittle (if solid), and poor conductors; tend to gain electrons.
• Metalloids: Elements with properties intermediate between metals and nonmetals (e.g., silicon, boron).
• Transition Elements: Metals found in the middle block ($\text{Groups } 3\text{--}12$) of the periodic table, often forming multiple ion charges.
• Noble Gasses: $\text{Group } 18$ elements; extremely unreactive due to having a full valence shell.

Chemical Quantities and Calculations

• Percent: A ratio expressing a part per $100$ of a whole.
• Density: Mass per unit volume of a substance:   $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$
• Specific Gravity: The ratio of the density of a substance to the density of a reference substance (usually water); has no units.
• Mole: The SI unit for amount of substance; equal to Avogadro's number of particles.
• Avogadro's Number: $6.022 \times 10^{23}$; the number of particles (atoms, molecules, ions) in one mole of a substance.
• Molecular Weight: The sum of the atomic weights of all atoms in a molecule (used for molecular compounds).
• Formula Weight: The sum of the atomic weights of all atoms in a formula unit (used more generally, including for ionic compounds).

Self-Check Review Tips

• Physical vs. Chemical Properties and Changes: Be able to distinguish physical vs. chemical for both properties and changes.
• Substance Classification: Know the difference between element, compound, mixture and where homogeneous/heterogeneous fit in.
• Periodic Table Navigation: Practice locating groups vs. periods and identifying metals, nonmetals, metalloids, transition elements, and noble gases on a periodic table.
• Subatomic Particle Properties: Memorize proton/neutron/electron charges, mass, and location.
• Quantitative Calculations: Practice mole, density, and percent calculations with correct significant figures and scientific notation.