Properties and States of Matter

Properties of Substances

• Substances are described by properties, categorized as physical or chemical.
• Physical properties are observable without changing the substance's identity (reversible).
  • Examples: color, hardness, conductivity, density.
• Physical properties can be intensive (independent of quantity) or extensive (dependent on quantity).
  • Examples: odor (intensive), volume (extensive).
• Chemical properties determine a substance's reactivity with others.
  • Examples: combining with other substances, changing color, emitting heat.

States of Matter

• Matter exists as solids, liquids, and gases.
• Solids: atoms packed tightly, fixed shape and volume.
• Liquids: loosely bonded atoms, indefinite shape, definite volume.
• Gases: atoms moving freely, indefinite shape and volume (compressible).
• Phase changes: transitions between states.
  • Melting: solid to liquid (increased energy).
  • Freezing: liquid to solid (decreased temperature).
  • Vaporization: liquid to gas (increased energy).
  • Condensation: gas to liquid (decreased energy).
• Changes can be physical (identity preserved) or chemical (new substances formed).
• Matter is conserved during both physical and chemical changes (Law of Conservation).

Atoms and Elements

• Atoms: basic units of matter.
• Structure: nucleus (protons, neutrons) and electron cloud.
• Subatomic particles: protons (positive), neutrons (neutral), electrons (negative).
• Atoms formed after the Big Bang.
• Elements: different types of atoms, distinct properties (determined by # protons).
• Models of the atom evolved over time.
• Atoms are submicroscopic (too small to see).

The Periodic Table

• Elements organized on the periodic table.
• Each element has an atomic number (equal to number of protons).
• Atomic number determines many element properties and reactivity.
• Elements combine to create all matter.

Isotopes

• Isotopes: different species of the same element (same atomic number, different mass).
  • Characterized by Frederick Soddy (1913).
• Two main types: stable and radioactive (unstable).
• Stability determined by proton/neutron ratio.
• Monoisotopic element: only one stable isotope.
• Half-life: rate of radioactive decay.
• Isotopic abundance: proportion of isotopes in nature (measured by mass spectrometry).
• Properties:
  • Same atomic number, different atomic masses.
  • Same chemical properties (mostly).
  • Different physical properties (often).
  • Can be stable or unstable.

Ions

• Ions: atoms that have gained or lost electrons, carrying a charge.
  • Cations: positive ions (lost electrons).
  • Anions: negative ions (gained electrons).
• Ions can be single atoms, molecules, or compounds.
  • Molecules: two or more of the same atoms bonded together.
  • Compounds: two or more different atoms bonded together.
• Monoatomic ions: one-atom ions.
• Polyatomic ions: multiple-atom ions.
• Atoms maintain their internal structure (nucleus, electron shells).
• Electrons are transferred to/from atoms, but protons are not.

Ionic and Covalent Compounds

• Compounds classified as ionic or covalent.
• Ionic compounds: metal cations and nonmetal anions.
  • Highly organized structures, high melting/boiling points, typically good conductors. Example: metal-nonmetal compound.
• Covalent Compounds: nonmetals sharing electrons.
  • Low melting/boiling points, typically poor conductors. Example: nonmetal-nonmetal compound.
• Chemical bonds join atoms in compounds.

Mixtures and Pure Substances

• Matter classified into mixtures and pure substances.
  • Pure substances contain only one type of compound per element.
  • Mixtures contain two or more compounds and/or elements.

Summary of Elements, Molecules, and Compounds

• Elements: one type of atom.
• Molecules: Atoms chemically bonded (same or different).
  • Bonds can be ionic or covalent.
• Compounds: two or more Different element types chemically bonded in fixed ratios.
  • Classified as ionic or covalent based on bond type.