ELECTRON CONFIGURATIONSAND

THE PERIODIC TABLE

Electron Configurations and the Periodic Table

• The electron configuration of an atom’s highest occupied energy level generally governs the atom’s chemical properties (the highest occupied level of the noble gases contain stable octets – outer s and p orbitals are completely filled with 8 electrons.

• The exception is helium (2 electrons in highest occupied energy level).

• Review valence electrons.

Periods and Blocks of the Periodic Table

• The elements are arranged vertically in the periodic table (groups) and horizontally (periods).• The length of each period is determined by the

number of electrons that can occupy the sublevels in that period.

• The period of an element can be determined from its electron configuration.• Example: Arsenic, As, has the electron

configuration [Ar] 4s23d104p3.• The highest occupied energy level is n=4 so As is in

the 4th period.

What about Molybdenum, Mo?

Electron configuration is [Kr] 5s24d4.

Period 5!!

• Based on the electron configuration of the elements, the periodic table can be divided into four blocks, the s, p, d, and f blocks.• The name of each block is determined by whether

an s, p, d, or f sublevel is being filled in successive elements of that block.

The s-Block Elements: Groups 1 and 2

• Elements in the same group share similar chemical properties.• Elements in groups 1 (alkali metals) and 2

(alkaline-earth metals) are chemically reactive.• The outermost energy level in an atom of each

Group 1 element contains a single s electron. This electron is lost with ease which helps to make these metals extremely reactive.• The outermost energy level in an atom of each

Group 2 element contains 2 s electrons. This makes them slightly less reactive.

•Group 1 elements have a silvery appearance and are soft enough to cut with a knife.• They combine vigorously with most nonmetals.• They are extremely reactive with air or moisture

and must be stored in kerosene.

•Group 2 metals are harder, denser, and stronger than group 1 metals.• They are also less reactive.• Although they are less reactive than alkali metals,

they are too reactive to be found in nature as free elements.

Calcium Barium

Hydrogen and Helium• Special cases in the classification of elements.•Hydrogen is located above Group 1 but has unique

properties.•Helium has configuration like Group 2 but is in

Group 18 due to chemical stability.

The d-Block Elements: Groups 3-12

• The d-block elements (transition metals) have metallic properties.• They are good conductors of heat and have a high

luster.

Copper Mercury Tungsten

• These elements are less reactive than the elements in Groups 1 and 2. • Some are so unreactive that they do not easily

form compounds, existing in nature as free elements.• Palladium, platinum, and gold are among the

least reactive of all the elements.

Palladium Platinum Gold

The p-Block Elements: Groups 13-18

• The properties of these elements vary greatly because the p-block consists of nonmetals, metals, and metalloids.•Group 17 (halogens) are the most reactive

nonmetals.• They react vigorously with most metals to form

salts.

Chlorine IodineBromine

• The metalloids have properties of metals and nonmetals.• They are the most brittle solids.

Silicon

• The metals are harder and denser than the metals in Groups 1 and 2, but softer and less dense than transition metals.•With the exception of bismuth, these metals are

sufficiently reactive to be found in nature only in the form of compounds.•Once obtained as free metals, however, they are

stable in the presence of air.

Bismuth Aluminum

The f-Block Elements: Lanthanides and Actinides

• Located between Groups 3 and 4 in the 6th and 7th periods.• Lanthanides are shiny metals similar in reactivity

to the Group 2 metals.

Cerium Europium

• Actinides are radioactive.• The first four have been found naturally on Earth

and the remaining actinides were made in a laboratory.

Uranium Thorium