Chemistry Notes on Matter, Atomic Structure, and the Periodic Table

Matter and Its Composition

  • Matter: Composed of atoms, elements, and compounds.
    • Element: Simplest type of matter, made of one type of atom.
    • Atom: Smallest part of an element; retains properties of the element.
    • Compound: Formed when atoms of different elements bond together.

Structure of Atoms

  • Nucleus:
    • Positively charged center of an atom contains protons and neutrons.
    • Accounts for most of an atom's mass.
  • Electron Cloud:
    • Region surrounding the nucleus.
    • Contains electrons, responsible for the atom's volume.
  • Subatomic Particles:
    • Protons: Positively charged, found in the nucleus.
    • Neutrons: Neutral, also located in the nucleus.
    • Electrons: Negatively charged, found in the electron cloud.

Electron Configuration

  • Energy Levels:
    • Defined lengths from the nucleus with increasing energy.
    • Electrons with more energy occupy levels farther from the nucleus.
  • Valence Electrons:
    • Electrons in the highest occupied energy level (outermost).
    • Stable configuration: typically 8 electrons (octet rule), except the first level can only hold 2.

Key Terms

  • Atomic Number: Number of protons in an atom, unique to each element.
  • Atomic Mass: Weighted average of the isotopes of an element.
  • Mass Number: Total of protons and neutrons in an atom ( Mass ext{ Number} = p + n ).

Ions

  • Ions: Atoms that have either gained or lost electrons.
    • Positive Ions (Cations): Formed when atoms lose electrons.
    • Negative Ions (Anions): Formed when atoms gain electrons (named by changing the element's suffix to "ide").

Periodic Table Basics

  • Periods: Horizontal rows indicating number of energy levels.
  • Groups/Families: Vertical columns; elements share similar properties.
    • Nonmetals gain electrons to form anions; metals lose electrons to form cations.

Atomic Radius and Trends

  • Atomic Radius:
    • Refers to the size of an atom; decreases across a period due to increased nuclear charge.
    • Increases down a group as new energy levels are added.
  • Ionization Energy (IE):
    • Energy required to remove an electron from an atom.
    • First Ionization Energy: Energy to remove the first electron, forming a 1+ ion.
    • Second Ionization Energy: Energy to remove the second electron, forming a 2+ ion.

Electronegativity and Trends

  • Electronegativity (EN): Ability of an atom to attract electrons in a bond.
    • Generally decreases down a group due to increased distance from the nucleus and increased shielding.
  • The trends of IE and EN are opposite of atomic radius.

Main Group Elements

  • Representative Elements: Groups 1, 2, 13-18 ("tall" groups).
  • Transition Metals: Groups 3-12, capable of forming multiple charges.
  • Inner Transition Metals:
    • Lanthanides (begin with La-57) and actinides (begin with Ac-89).

Properties of Elements

  • Metallic Properties:
    • Luster, good electrical/thermal conductors, malleable, and ductile (solids at room temperature except mercury).
  • Nonmetal Properties:
    • Dull appearance, often brittle, poor conductors (good insulators), gases or solids at room temperature.
  • Metalloids:
    • Have mixed properties, often semiconductors useful in electronics.