Chemical Foundations

• CHEMISTRY is the study of matter and the changes it undergoes.
• Substance


  A form of matter that has a definite composition and distinct properties.
• Element


  Consists of identical atoms.
• Compound


  Made up of two or more elements in a fixed ratio by mass.
• Examples of compounds

  • Sugar (C12H22O11)
  • Water (H2O)
  • Gold (Au)
• Diatomic elements


  • H2
  • N2
  • O2
  • F2
  • Cl2
  • Br2
  • I2
• Polyatomic elements


  • O3
  • P4
  • S8
• Diamond has millions of carbon atoms bonded together to form one gigantic cluster.
• Mixture


  A combination of two or more substances in which the substances retain their distinct identities.
• Homogeneous mixture


  Composition of the mixture is the same throughout.
• Heterogeneous mixture


  Composition is not uniform throughout.
• Examples of homogeneous mixtures


  • Soft drink
  • Milk
  • Solder
• Examples of heterogeneous mixtures

  • Iron filings in sand
  • Blood
• John Dalton’s Atomic Theory states that all matter is composed of very tiny particles called atoms.
• Atoms of the same element


  Have the same chemical properties.
• Atoms of different elements

  Have different chemical properties.
• In a chemical reaction, no atom of any element disappears or is changed into an atom of another element.
• Law of conservation of mass

  Discovered by Antoine Lavoisier; matter can be neither created nor destroyed.
• Compounds


  Formed by the chemical combination of two or more of the same or different kinds of atoms.
• Molecule


  A tightly bound combination of two or more atoms that acts as a single unit.
• Law of constant composition

  Any compound is always made up of elements in the same proportion by mass.
• Sample proportions


  • 2 parts Hydrogen
  • 1 part Oxygen
• Different compounds made up of the same element differ in the number of atoms of each kind that combine.
• The unit of mass is given in atomic mass units (amu).
• One amu is defined as the mass of an atom of carbon with 6 protons and 6 neutrons in its nucleus.
• 1 amu = 1.6605 x 10-24 g.
• Mass number (A)


  The sum of the number of protons and neutrons in the nucleus of an atom.
• Atomic number (Z)


  The number of protons in the nucleus of an atom.
• Isotopes


  Atoms with the same number of protons but a different number of neutrons.
• Most elements found on Earth are mixtures of isotopes.
• Chlorine is 75.77% chlorine-35 (18 neutrons) and 24.23% chlorine-37 (20 neutrons).
• Atomic weight


  The weighted average of the masses (in amu) of the naturally occurring isotopes of an element.
• The periodic table is a chart showing all the elements arranged in columns with similar chemical properties.
• Dmitri Mendeleyev


  Arranged the known elements in order of increasing atomic weight and observed that certain sets of properties recur periodically.
• Electrons


  Are confined in specific regions of space called principal energy levels/shells (n = 1, 2, 3…).
• The closer an electron is to the nucleus, the harder it is to remove from the atom.
• Subshells


  Shells are divided into subshells (s, p, d, f) which define the shape of the orbital.
• Subshells and their capacities

  • s: 1 orbital, 2 electrons
  • p: 3 orbitals, 6 electrons
  • d: 5 orbitals, 10 electrons
  • f: 7 orbitals, 14 electrons
• Degenerate orbitals are orbitals that have the same energy.
• Energy of an orbital is influenced by the size and shape of the orbital.