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Chem 109A Chapter 1.2 Notes

Matter

  • Matter is the stuff in the universe that has mass and occupies volume.
  • Includes everything with physical substance; synthetic atoms are man-made.
  • Key idea: matter occupies space and has mass (and inertia).

States of Matter

  • States include solid, liquid, gas, plasma, and Bose-Einstein condensate (often lab-made).
  • Plasma: high-energy state where electrons are separated from nuclei; common in stars and some lab plasmic conditions.
  • Bose-Einstein condensate: a state of matter achieved at ultra-low temperatures where particles occupy the same quantum state.

Composition and Properties

  • Composition: parts or components of matter.
  • Properties: observable characteristics of matter.

Solids

  • Particles are tightly packed.
  • Defining features: vibrational motion with limited translational motion.
  • Maintain shape and volume.
  • Examples: Diamond, coal.

Liquids

  • Particles have more space between them than in a solid.
  • Flows and takes the shape of the portion of the container it occupies.
  • Particles exhibit vibrational motion and limited translational motion.
  • Have definite volume but shape adapts to container.

Gases

  • Large spaces between particles.
  • Easily compressed.
  • Particles exhibit vibrational, rotational, and translational motion.
  • Flows easily and expands to fill the shape and volume of its container.

Phase Coexistence

  • Matter can exhibit all three states at the same time (e.g., an ice cube melting has solid ice, liquid water, and water vapor at the surface during phase change).

Atoms

  • Basic units of matter.
  • Electrons form an electron cloud around the nucleus (negative charge).
  • Nucleus contains protons and neutrons (collectively, nucleons).
  • Protons and neutrons have mass; their masses are similar but not identical and do not need to be treated precisely for basic chemistry.

Elements

  • A pure substance that contains only one type of atom.
  • There are 118 elements discovered so far.
  • When an element is neutral, it has the same number of protons and electrons.
  • Learn the elements and their symbols up to the sixth row of the periodic table.

Periodic Table Families (basic ideas mentioned in the lecture)

  • Noble gases: Group 18 (often referred to as row 18 in older notes); they are largely nonreactive.
  • Alkali metals: Group 1 (first column of the periodic table).
  • Alkaline earth metals: Group 2 (second column).

Molecules

  • Molecules: two or more atoms chemically combined in specific geometric arrangements.
  • Diatomic molecules: contain exactly two atoms.
  • If the two atoms are the same, the molecule is an element (not a compound).

Seven diatomic molecules

  • There are seven diatomic molecules in nature:
  • H2,\, N2,\, O2,\, F2,\, Cl2,\, Br2,\, I_2
  • These diatomic forms often exist as elemental species (e.g., H2, N2, O2) in the environment.

Additional context and connections

  • These concepts form the foundation for understanding materials, reactivity, and chemical bonding.
  • Real-world relevance: - Material properties (solids vs liquids vs gases) affect everything from engineering to biology.
  • Elements and diatomic molecules explain why air is primarily N2 and O2, and why certain elements are inert (noble gases).

Notable clarifications

  • The term “row 18” is an older way of pointing to the noble gases; the standard modern reference is Group 18. Noble gases are largely unreactive due to complete valence electron shells.
  • When discussing states, plasma and Bose-Einstein condensates are more advanced states that are typically observed under special conditions.
  • The seven diatomic molecules are the only diatomic molecules that exist with identical atoms in stable elemental form at standard conditions.

Quick reference (numbers and symbols)

  • Elements discovered so far: 118
  • Diatomic molecules: H2,\, N2,\, O2,\, F2,\, Cl2,\, Br2,\, I_2
  • Nomenclature reminders:
    • Atom types: proton(s) + neutron(s) in nucleus; electrons in surrounding cloud
    • Neutral atom: Z = P = E (protons = electrons)

Practical implications

  • Understanding states of matter helps predict behavior under changes in temperature and pressure (e.g., compression, heating).
  • Knowing diatomic molecules clarifies why certain elements exist as gases or liquids under ambient conditions.
  • Recognizing noble gases as largely inert explains their limited chemistry and why they’re used in lighting, inert atmospheres, etc.