Periodic Table

• When you hear the word "Chemistry", one of the things that comes to mind is probably the periodic table of the elements
• Development of the periodic table

  1. Dobereiner proposed the model of triads or the law of triads in 1829

  2. Newland's law of octaves in 1864

  3. Mendeleev and Meyer formulated the periodic table
• Dobereiner's triad


  • Lithium, Sodium, Potassium
  • Chlorine, Bromine, Iodine
  • Sulfur, Selenium, Tellurium
• Dobereiner's model was followed by John Newland's law of octaves in 1864
• Mendeleev was given most of the credit for the periodic table because of his insistence on how important the table is
• Periods


  Rows in the periodic table
• Groups/Families


  Columns in the periodic table
• Types of elements in the periodic table

  • Representative elements (groups 1, 2, 3-17)
  • Transition metals (groups 3-12)
  • Boron group (group 13)
  • Carbon group (group 14)
  • Pnictogens (group 15)
  • Chalcogens (group 16)
  • Halogens (group 17)
  • Noble gases (group 18)
  • Lanthanides
  • Actinides
• Alkali metals (group 1)


  • Highly reactive
  • Possess a single electron in their outermost shell
  • Readily lose one electron to form ions with a +1 charge
• Alkaline earth metals (group 2)


  • Have two electrons in their valence shell which they readily lose to form cations with +2 charges
• Groups 1 and 2 are sometimes referred to as the s block elements
• Noble gases (group 18)


  • Have completely filled p subshells (except He)
  • All members have 8 electrons in their valence shell
  • Chemically inert
  • Colorless, but can emit bright colors when ionized
• Transition metals (groups 3-12)


  • Generally characterized by partially filled d subshells or those which can give rise to cations with an incomplete d subshell
  • Sometimes called the d block elements
• Some transition metals can form cations with multiple oxidation states
• Boron group (group 13)


  • All have three electrons in their outermost shell
  • Form cations with a +3 charge upon ionization
• Carbon group (group 14)


  • Elements are characterized by 4 electrons in their outermost shell
• Pnictogens (group 15)


  • All have 5 valence electrons
  • Aside from nitrogen, pnictogens are solid at room temperature
• Chalcogens (group 16)


  • Composed of electronegative nonmetals and metalloids
  • All have 6 electrons in their outermost shell
• Halogens (group 17)


  • The only group in the periodic table with members existing as gas (fluorine and chlorine), liquid (bromine), and solid (iodine and astatine) at room temperature
  • Have 7 electrons in their outermost shell
  • Readily accept an electron to form anions with a -1 charge
• Groups 13-18


  • Collectively known as the p block elements
  • Composed of metals, nonmetals, and metalloids
• Metalloids


  • Elements with properties that are intermediate to both metals and nonmetals
  • Used in the manufacturing of semiconductors
• Lanthanides


  • Also known as rare earth elements
  • Naturally occurring elements but exist in extremely small amounts
  • Have incompletely filled 4f subshells or form cations with incompletely filled 4f subshells
• Actinides


  • All radioactive
  • Heavy elements that are not naturally occurring
  • Have incompletely filled 5f subshells or form cations with incompletely filled 5f subshells
• Atomic radius generally increases down the group and decreases across a period from left to right
• Electronegativity increases as you approach fluorine (i.e., electronegativity increases across a period from left to right, and decreases down the group)
• Ionization energy decreases down a group and increases across a period from left to right
• Electron affinity increases from left to right of the periodic table and decreases down the group
• Electrons in the valence shell of smaller atoms are closer to the nucleus, resulting in a stronger attraction and higher electron affinity
• Hypothesis 1: All matter consists of indivisible particles called atoms.
• Hypothesis 2: All atoms of the same element are identical in terms of size, mass, and chemical properties. The atom of one element is different from the atom of another element.
• Hypothesis 3: Atoms of different elements may combine in fixed proportions to form a compound.
• Hypothesis 4: Chemical reactions involve reorganization of the atoms—changes in the way they are bound together. The atoms themselves are not changed in a chemical reaction.
• John Dalton proposed that all matter consisted of tiny, indestructible spheres called atoms.
• The law of conservation of mass states that during any chemical change, there is no net loss or gain of mass.
• Dalton's atomic theory was based on observations made by other scientists at the time.
• Atomic number (Z) - Number of protons in an atom
• Mass number (A) - Sum of neutrons and protons in an atom
• Isotopes - Different forms of an element with the same number of protons but different numbers of neutrons
• Periodic table - Arrangement of elements according to increasing atomic number
• Periodicity - Patterns observed when elements are arranged in order of increasing atomic number