Chemical Periodicity

History• Dmitri Mendeleev (1834 – 1907)

– Russian chemist– Noticed regular (periodic) recurrence of chemical and physical

properties after arranging by increasing atomic mass.• Eventually led to grouping by similar properties side by side

Predicted properties of then unknown elements with amazing accuracy.• Henry Mosely (1887 – 1915)

– British physicist– Identified atomic number (nuclear charge) of the atoms of elements

• Arranged periodic table by atomic number

Current arrangement of periodic table

The Periodic Table

• Periods – horizontal rows of the periodic table.

• Groups – vertical columns of the periodic table.

• Periodic Law – when the elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties.

Electron Configuration/Periodicity1. Noble gases

– Outermost p and s sublevels are filled

2. Representative elements– Outermost p and s sublevels are only partially filled– Called the Group A elements

1. Alkali metals – group 1A2. Alkaline earth metals – group 2A3. Halogens – group 7A

3. Transition metals– Outermost s sublevel and the nearby d sublevel contains electrons– Called the group B elements

4. Inner transition metals– Outermost s sublevel and the nearby f sublevel generally contain electrons

Atomic Radius

• = half the distance between the nuclei of two like atoms.

• Atomic size generally increases as you move down a group.

• Atomic size generally decreases as you move from left to right across a period.

Largest atoms are towards the bottom and to the left of the periodic table.

Ionization Energy

• = The energy that is required to overcome the attraction of the nuclear charge and remove an electron from a gaseous atom.

• Ionization energy decreases as you move down a group of the periodic table.

• For the representative elements, ionization energy generally increases as you move from left to right across a period.

Electronegativity

• = the tendency for the atoms of the element to attract electrons when they are chemically combined with another element.

• Electronegativity increases for the representative elements as you move from left to right and generally decreases as you move down a group.