1. Periodicity
Chapter 5

2. The History of the Development of the Periodic Table
In the 1790’s Antoine Lavoisier (French Chemist) compiled a list of 23 elements. Some of these were gold, silver, carbon, oxygen. In 1860 Stanislao Cannizzaro (Italian chemist) presented a method for accurately measuring the relative masses of atoms. In 1864 John Newlands(English Chemist) noticed that when elements were arranged by increasing atomic mass, their properties repeated every eighth element. He called this the Law of Octaves

3. Lothar Meyer and Dimitri Mendeleleev
In 1869 Lothar Meyer (German chemist) and Dmitri Mendeleev (Russian chemist) each demonstrated a connection between atomic mass and elemental properties.
However, Mendeleev produced the first useful and widely accepted periodic table arranged in order of increasing atomic mass.
An important facet of his table was that he left blank spaces in the table where he thought undiscovered elements should go.
Mendeleev is considered the “father” of the periodic table.

4. Properties of some elements predicted by Mendeleev
Predicted elements
Element & year discovered
Properties
Predicted properties
Observed properties
Ekaaluminum
Gallium
1875
Density of metal
6.0 g/ml
5.96 g/ml
Melting point
Low
30 °C
Oxide formula
Ea2O3
Ga2O3
Ekaboron
Scandium
1877
3.5 g/ml
3.86 g/ml
Eb2O3
Sb2O3
Solubility of oxide
Dissolves in acid
Ekasilicon
Germanium
1886
High
900°C
5.5 g/ml
5.47 g/ml
Color metal
Dark gray
Grayish white
EsO2
GeO2
Density of oxide
4.7 g/ml
4.70 g/ml
Chloride formula
EsCl4
GeCl4

5. Henry Moseley
In 1913 Henry Moseley(English chemist) discovered that atoms of each element contain a unique number of protons in their nuclei—the number of protons being equal to the atom’s atomic number. He proposed the Periodic Law, which states that there is a periodic repetition of chemical and physical properties of the elements when they are arranged by increasing atomic number. His arrangement of elements by atomic number resulted in a clear periodic pattern of properties. This is the basis of the Modern Periodic Table which we are using now.

6. Periodic Law: The physical and chemical properties of the elements are periodic functions of their atomic numbers. This periodicity in properties of the elements is a function of the arrangement of electrons around the nucleus of an atom (remember that the # of electrons = the # of protons in a neutral atom)
  Valence electrons: The electrons available to be lost, gained, or shared in the formation of chemical compounds; i.e. the “outer shell” electrons.

7. Periodic trends
Atomic radii: one half the distance between the nuclei of identical atoms that are bonded together.

8. Atomic radii vs. atomic number

9. Atomic Radii vs. atomic number

10. Cations

11. Anions

13. Ionization energy
The energy required to remove one electron from a neutral atom or an element. (kJ/mol)
A + energy  A+ + e-

16. A + e-  A- + energy A + e- + energy  A-
Electron Affinity
The energy change that occurs when an electron is acquired by a neutral atom.
Most atoms RELEASE energy when they acquire an electron.
A + e-  A- + energy
Some atoms must be “forced” to gain an electron by the addition of energy.
A + e- + energy  A-

18. Electron affinity vs. atomic number

19. a measure of the ability of an atom in a chemical compound to attract
Electronegativity
a measure of the ability of
an atom in a chemical
compound to attract
electrons. Highest value is
arbitrarily given to
Fluorine of 4.0.

20. Electronegativity

22. Electronegativity vs. atomic number

23. General reactivity trends