Chemistry Chapter 5 The Periodic Law

History of the Periodic Table Stanislao Cannizzaro (1860) method of accurately measuring the relative mass of an atom Dmitri Mendeleev (1869) heard about the new atomic masses and decided to put them in a chem book he was writing

Mendeleev ’ s Periodic Table 1869 Dmitri Mendeleev

Arranged elements in order of increasing atomic mass. Predicted the existence of elements that would fill 3 of the spaces. Within 15 years, those elements had been discovered (scandium, gallium, and germanium)

Henry Moseley 40 years later; discovered a better pattern arranged elements in increasing order of atomic number (number of protons) Periodic Law – The phys and chem properties of the elements are periodic functions of their atomic numbers (credit given to Mendeleev); elements with similar properties appear at regular intervals

Periodicity of Atomic Numbers

Modern Periodic Table Elements arranged in order of their atomic numbers so that elements with similar properties fall into the same column or group.

Periodic Table with Group Names

Hydrogen and Helium Hydrogen does not share the same properties as the elements of group 1. Helium has the electron configuration of group 2 elements however it behaves like group 18 (Noble Gases)

Li, Na, K, Rb, Cs, Fr VERY REACTIVE (1 valence e-) Silvery appearance Soft (cut with a knife) React violently with water React with halogens to form salts Usually stored in kerosene Group 1 Alkali Metals

Group 2 Alkaline Earth Metals Be, Mg, Ca, Sr, Ba, Ra 2 valence electrons Less reactive but still too reactive to be found in nature as free elements. Harder, denser, and stronger than alkali metals. Higher melting points

Groups 3-12 Transitions Metals d-block elements good conductors of electricity high luster less reactive than the alkali metals and the alkaline earth metals. Some deviations from orderly d sub- level filling occur in groups 4-11

Groups Main Group Elements p-block elements Properties vary greatly Metals & Nonmetals Contains all six metalloids (B, Si, Ge, As, Sb, and Te)

Group 17 Halogens F, Cl, Br, I, and At 7 valence electrons React vigorously with most metals most reactive of the nonmetals

Group 18 Noble Gases He, Ne, Ar, Kr, Xe, Rn 8 valence electrons (Octet of electrons) Very Stable – does not react

f-block elements Lanthanides & Actinides Lanthanides – shiny metals Actinides – radioactive; only the 1st four are found naturally