Chapter 5:  THE PERIODIC LAW

Development of the Periodic Table

I.  John Dalton was the first to try to arrange the known elements into an organized chart based on his masses of comparison.

II.  Jons Jakab Berzelius made measurements of relative masses of known elements and developed the modern system for       element symbols and how to write chemical formulas.

III.  German Johann Dobereiner in 1817 grouped elements in three's called a triad.  These were related elements and had similar properties.  He determined that the middle element's       properties - such as boiling point, freezing point, mass,    atomic number, density, etc. - seemed to be an average of the outside two.

IV  Englishman John Newlands - 1864

      A.  arranged by increasing atomic masses

      B.  repeat of similar properties every eighth element

      C.  arrangement of seven rows of seven each

      D.  Law of Octaves: every eighth element had repeating properties when the elements were arranged in order of their increasing atomic masses.

      E.  ridiculed for his work by his peers and none of his work was accepted by the science community

V.  Russian Dmitri Mendeleev and German chemist Lothar Meyer - 1869

      A.  worked independently on same concept, but Mendeleev's work proved to be more useful

      B.  arrangement by increasing atomic masses but rows of varying numbers

      C.  Mendelev was able to predict the properties of elements that had not been discovered yet based on their position in the periodic table - Germanium (Ekasilicon), Gallium, and Scandium

      D.  Periodic Law:  elements are organized into columns by their repeating properties if arranged by their increasing   atomic masses

      E.  inconsistencies with his table - holes in the table - when some of the elements were placed by their increasing masses, they did not fit into the correct column - mass measurements must be incorrect   

VI.  Henry Moseley

      A.  X-ray experiments:  number of protons identifies element

      B.  Periodic Law revision:  properties of elements are a periodic function of their atomic numbers

VII.  F.W. Astom - 1922 - isotopes

VIII. Glenn Seaborg - 1944 - actinide series

IX.  new arrangements

 

Periodic Properties and Trends

I.  Periodic Law:  properties of elements are a periodic function of their atomic numbers

II.  Atomic numbers are equal to the number of protons and therefore equal to the number of electrons

III.  The numbers of electrons determines the electron configurations

IV.  The electron configuration determines the properties of elements

V.  Horizontal rows of the periodic table

      A.  called periods

      B.  numbered 1, 2, ...7

      C.  in general,  filling of the energy levels

            1.  s's are filling the energy level equal to the row number      

            2.  p's are filling the energy level equal to the row number           

            3.  d's are filling the energy level equal to the row number minus 1  (because the outer energy level is the row number)              

            4.  f's are filling the energy level equal to the row number minus 2  (because the outer energy level is the row number)

VI.  Vertical columns of the periodic table

      A.  called groups or families

      B.  numbered

            1.  traditional system

                  a.  main group elements numbered with a Roman numeral and A:  IA - VIIA

                  b.  transition elements numbered with a Roman numeral and B: (from left to right) 

                        IIIB - VIIB, three columns of VIIIB and then IB and IIB

            2.  modern system:  number from 1 - 18 or 1 - 17, 0

VII.  Electron configurations:

      A.  in general,  filling of the last electron

            1.  Elements in the first main vertical column end with s¹

            2.  Elements in the second main vertical column end with s²

            3.  Elements in the third main vertical column end with p¹

            4.  Elements in the fourth main vertical column end with p²

            5.  Elements in the fifth main vertical column end with p³

            6.  Elements in the sixth main vertical column end with p⁴

            7.  Elements in the seventh main vertical column end with p⁵

            8.  Elements in the eighth main vertical column end with p⁶

            9.  Elements in the dropped center columns end with d¹ - d¹⁰

            10.  Elements in the two rows at the bottom end with f¹ - f¹⁴

      B.  EXCEPTIONS: 

            1.  full or half-full sublevels are slightly more stable than an atom with no special arrangement

                  a.  chromium:  should be ... 4s² 3d⁴, it is observed to be ... 4s¹ 3d⁵ ;  molybdenum is explained like chromium

                  b.  copper:  should be ... 4s² 3d⁹, it is observed to be ... 4s¹ 3d¹⁰ ;  silver and gold are explained like copper

            2.  lanthanide series:  La ^#57 – Yb ^#70

            3.  actinide series:  Ac ^#89 – No ^#102

      C.  Outer energy levels

            1.  outer energy levels are s's and p's

            2.  together an s and a p can hold a maximum of eight electrons

            3.  energy levels with eight electrons are considered full

            4.  Octet rule:  atoms with eight electrons in the outer energy level is particularly stable.  

                  a.  Noble gases have eight electrons in their outer energy level  (except helium, it has only two which is all it can have and makes the first level filled).  So a noble gas configuration  is stable. 

                  b.  Atoms combine and ions are formed to become more stable and satisfy the octet rule  (so the atom's electron configuration is a noble gas configuration). 

VIII.  Group names

      A. Main group elements

            1.  hydrogen, unique, a family all it's own, can be included in IA or in VIIA

                  a.  loose one electron       

                  b.  share one electron       

                  c.  gain one electron        

                  d.  forms bridges - not common

            2.  alkali metals,  IA

                  a.  most reactive metal family       

                  b.  forms binary ionic compounds with most nonmetals        

                  c.  most group IA compounds are soluble         

                  d.  forms a base when mixed with water

            3.  alkaline earth metals,  IIA

                  a.  very reactive              

                  b.  compounds are mainly ionic          

                  c.  most IIA compounds are soluble in water

                  d.  forms a base when mixed with water

            4.  pnictogens, VA

            5.  chalcogens,  VIA

                  a.  tend to gain two electrons to form ions         

                  b.  also tends to share electrons

            6.  halogens,  VIIA

                  a.  most reactive nonmetal family,  fluorine is the most reactive element of all the chemical elements              

                  b.  gain one electron              

                  c. gain also share electrons

            7.  noble gases  (inert gases),  VIIIA

                  a.  not  chemically "inert"            

                  b.  xenon first to form compounds, krypton and radon also form compounds

      B.  other groups are named by the element at the top of the column

            1.  boron family,  IIIA

                  a.  more likely to share electrons than form ions       

                  b.  less metallic than IA and IIA          

                  c.  less reactive than IA and IIA

            2.  carbon family,  IVA

                  a.  generally react by sharing electrons        

                  b.  have more than one oxidation number

IX.  Areas

      A.  metals

            1.  to the left of the Zintl border          

            2.  hard       

            3.  metallic luster, shiny        

            4.  conduct heat and electricity            

            5.  generally elements with three or less electrons in the outer  (highest) energy level      

            6.  lose electrons to form positive ions       

            7.  positive ions smaller than neutral atom

      B.  nonmetals

            1.  to the right of the Zintl border        

            2.  at room temperatures, gases or brittle solids        

            3.  dull surfaces

            4.  insulators, poor conductors of heat and electricity       

            5.  generally elements with five or more electrons in the outer  (highest)  energy level           

            6.  gain electrons to form negative ions       

            7.  negative ions larger than neutral atom

      C.  metalloids

            1.  elements on the Zintl border, except aluminum         

            2.  show properties of metals and nonmetals,  ie. silicon and germanium are semi-conductors  

      D.  transition metals,  IIIB - IIB - used as structural elements

      E.  rare earth metals

            1.  lanthanide series        

            2.  actinide series

X.  Metallic character

      A.  in general,  metallic character tend to increase in size from right to left across a period

      B.  in general, metallic character tend to increase in size from top to bottom down a group

XI. Atomic radii

      A.  in general,  atomic radii tend to increase in size from right to left across a period:  with the addition of one more proton, the electron is pulled in more tightly - smaller electron cloud

      B.  in general,  atomic radii tend to increase in size from top to bottom down a group:  each additional row is one more energy level - the size of the electron cloud increases

XII.  Ionic radii

      A.  ions are formed to make the atom's electron configuration like a noble gas configuration

      B.  positive ions

            1.  loose electrons to "look like" the noble gas preceding it on the table

            2.  the ion is smaller than the atom forming it

      C.  negative ions

            1.  gain electrons to "look like" the noble gas following it

            2.  the ion is larger than the atom forming it

XIII.  Oxidation numbers: the tendency to gain or loose electrons to gain a "noble gas electron configuration"

      A.  metals tend to form positive ions

            1.  IA = +1       

            2.  IIA = +2      

            3.  IIIA = +3           

            4.  IVA = +2 or +4         

            5.  transition metals vary, tend to have more than one oxidation number          

            6.  lanthanide series = +3       

            7.  actinide series = +3 or +4

      B.  nonmetals tend to form negative ions

            1.  VA = -3       

            2.  VIA = -2      

            3.  VIIA = -1

      C.  noble gases don't tend to form ions, oxidation number = 0

      D.  compounds:  because elements in the same column tend to have the same oxidation numbers we can assume that they will also react similarly and therefore form similar compounds

XIV.  Ionization energy

      A.  energy needed to remove an electron from a gaseous atom

            1.  first ionization energy - energy to remove the most loosely held electron

            2.  multiple ionization energies - energy needed to remove the second, third, fourth, etc. electrons

      B.  in general,  the first ionization energy tends to increase from left to right across a period: metals are characterized by having low ionization energies

      C.  in general,  the first ionization energy tends to increase from bottom to top up a group: nonmetals are characterized by having high ionization energies

      D.  factors that affect ionization energy

            1.  nuclear charge:  greater nuclear charge = greater ionization energy

            2.  shielding effect:  greater number of electrons between the nucleus and the electron = lower ionization energy

            3.  radius of the atom:  greater radius = lower ionization energy

            4.  sublevel stability:  filled or half-filled = greater ionization energy

XV.  Electron affinity

      A.  the energy change (energy is released) when a neutral gaseous atom gains an electron

      B.  in general,  the electron affinity tends to increase from left to right across a period:  metals are characterized by  having low electron affinities

      C.  in general,  the electron affinity tends to increase from bottom to top up a group:  nonmetals are characterized by having high electron affinities

XVI.  Electronegativity

      A.  the ability of an atom to attract electrons to itself when it is in a chemical bond

      B.  in general,  the electronegativity tends to increase from left to right across a period:  metals are characterized by  having low electron affinities

      C.  in general,  the electronegativity tends to increase from bottom to top up a group:  nonmetals are characterized by having high electron affinities

XVII.  Allotropes:  different forms of the same element,  can have different propertiew

      A.  carbon

            1.  diamond       

            2.  graphite

      B.  oxygen

            1.  diatomic,  O₂      

            2.  ozone,  O₃

      C.  phosphorus, occurs as P₄

            1.  white           

            2.  red        

            3.  black

      D.  sulfur, S₈ 

            1.  ring

            2.  amorphous

XVIII.  Reactions:  elements in the same family tend to react the same way and tend to form the kinds of compounds with     the same mole ratio