CHEMICAL PERIODICITY
A. The Periodic table Revisited
1. 1871- Mendeleev developed the first table based on atomic mass
2. Modern table based on atomic number
3. Elements in families (columns) have similar properties
B. Classifying elements by electron configurations
1. electrons play the biggest role in physical & chemical properties of each element
2. Four categories based on electron configs
a. Noble Gases --> elements with filled outer shell s & p sublevels
Helium = 1s2 Neon = 1s2,2s2,2p6 Argon = 1s2,2s2,2p6,3s2,3p6
1. This is the reason that they do not react with other elements
b. representative elements --> elements with partially filled s & p sublevels
Lithium = 1s2,2s1 Carbon = 1s2,2s2,2p2
1. Includes alkali metals, alkaline earth metals, other metal, nonmetals, and halogens
2. Group number = number of electrons in outer energy level
Group 1A = 1 e-(Li) Group %A = 5 e-(N)
c. Transition Metals --> metallic elements with outer shell electrons in s & d sublevels
1. add electrons to the d orbitals
d. Inner Transition Metals --> metallic elements with outer shell electrons in s & f sublevels
1. add electrons to the f orbitals
3. Periodic Table Trends
a. s-block --> group 1A and 2A
b. p-block --> group 3A - 0 (8A)
c. d-block --> transition metals
d. f-block --> inner transition metals
e. Period corresponds to the principal energy level
1. d-block --> principal energy level is one less than period #
2. f-block --> principal energy level is two less than period #
II. Periodic Trends
A. Trends in Atomic Size
1. Atomic radii --> 1/2 the distance between the nuclei of two like atoms in a diatomic molecule
a. Indicates relative size of atoms
2. Group trend - atomic radii increase going down a group
a. Reason: new energy levels added & increased shielding (blocking attraction of protons on the outer shell electrons by inner shell electrons)
3. Periodic Trend - decrease going across a period
a. Reason: increase attractionbetween proton and electron when more are added
B. Trends in Ionization Energy
1. Ionization energy --> energy required to overcome attractive forces of the nucleus to remove an electron from a gaseous element
a. Remove 1st electron = 1st ionization energy
b. Remove 2nd electron = 2nd ionization energy
2. Group trend - decreases going down a group
a. Reason: outer electron is farther from nucleus, easier to remove
3. Periodic trend - increases going across a period
a. Reason: increased attraction between protons and electrons when more are added
C. Trends in Ionic Size
1. Metals make positive ions, Nonmetals make negative ions
2. Group trend - increases going down a group
a. Reason: extra energy level, increased shielding
b. Cations are smaller than neutral atoms
1. Less electrons, greater attraction between protons & electrons
c. Anions are larger than neutral atoms
1. More electrons, less attraction between protons & electrons
3. Periodic Trend - decreases going across a period
a. Reason: increased attraction between protons and electrons when more are added
D. Trends in electronegativity
1. Electronegativity --> the tendency for atoms of an elements to attract electrons when chemically combined
a. Arbitrary scale set up called the Pauling electronegativity scale
b. Excludes Noble gases since they do not react
2. Group trend - decreases going down a group
a. Reason: low attraction between protons and outer electrons due to shielding and extra energy levels
3. Periodic trend - increases going across a period
a. Reason: greater attraction betwen protons and outer electrons as more are added
4. We will use electronegativity values to predict bond types in chapters 15-16
Outline based upon:
Matta, M. S., Staley, D. D., Waterman, E. L., & Wilbraham, A. C. (2000). Chemistry, Addison-Wesley. (5th ed.). Menlo Park, CA: Prentice Hall, pp. 391-407.
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