Arrangement of the Periodic Table

Vertical columns Called groups or families Contain elements with similar chemical and physical properties

Horizontal rows Called periods The length of a period is determined by the number of electrons that can occupy the orbitals filled in that period Properties vary as you move across a period

The table is arranged in blocks – s,p,d, and f Based on the electron configuration of each element The highest occupied energy level is the period in which the element is found

s-block elements The s-block elements include groups 1 and 2 as well as hydrogen and helium.

Group 1 Alkali metals Silvery in appearance Soft enough to cut with a knife Very reactive Not found in nature as free elements Combine vigorously with most non-metals and water When isolated, they must be store in kerosene to prevent them from reacting with air or moisture

Group 2 Alkaline-earth metals Pair of electrons in outermost s orbital Harder, denser, stronger than alkali metals Less reactive than alkali metals, but still too reactive to be found in nature as free elements

Hydrogen and Helium Hydrogen does not share the same properties as the elements of group 1. It is a unique element with properties that don’t resemble those of any group. Helium has its outermost energy level full with just 2 electrons. It is placed in group 18 with the other elements with full outer shells (noble gases)

d-block elements Transition elements (or transition metals) Good conductors, high luster Less reactive than group 1 or group 2 metals Some are so unreactive that they rarely form compounds Palladium, platinum, and gold are among the least reactive

p-block elements All have a full s-orbital in outermost energy level, and at least one electron in a p orbital. Properties vary greatly Include metals (left and bottom of block) Nonmetals (right side) Metalloids (boron, silicon, germanium, arsenic, antimony, and tellurium)

The metals of the p-block are harder and denser than the alkaline earth metals, but softer and less dense than the transition metals.

The metalloids are mostly brittle solids with some properties of metals and some of nonmetals. Electrical conductivity is in between that of metals and nonmetals – they are called semiconductors.

All the nonmetals except hydrogen and helium are found in the p block. They include the halogens and the noble gases.

Halogens The halogens are group 17. They are the most reactive nonmetals React vigorously with most metals to form salts. At room temperature, fluorine and chlorine are gases, bromine is a reddish liquid, and iodine is a dark-purple solid.

Noble gases Group 18 Nonreactive because their outermost energy level is full with an octet of electrons. Except helium which is full with just 2 electrons

f-block elements Lanthanides and actinides Fall between groups 3 and 4, but do NOT belong to any group themselves. Lanthanides are shiny metals which are similar in reactivity to the alkaline earth metals Actinides are all radioactive and all but the first 4 are synthetic.