Periodic Law Chapter 5

Dmitri Mendeleev 1st to organize elements into groups based on their properties, looking for trends or patterns. Noticed the elements were organizing in order of increasing atomic masses.

Dmitri Mendeleev Certain similarities in the elements began to appear at regular intervals (periods). He left several spaces between elements, for elements not yet discovered, noting there should be elements that fit into the patterns and will be placed in the empty spaces.

Dmitri Mendeleev

Henry Moseley and Periodic Law 1911 Henry Moseley discovered a pattern when working with the periodic elements. He found the elements fit into a better pattern when arranged by increasing atomic numbers. Moseley discovery was consistent with Mendeleev, which led to the Periodic Law.

Periodic Law Definition – the physical and chemical properties of the elements are periodic functions of their atomic numbers. In other words, when elements are arranged in order of increasing atomic number, elements with similar properties appear at regular intervals (periods).

Periodic Table Definition – an arrangement of the elements in order of their atomic numbers so that elements similar properties fall in the same column or group. Periodic Table arranged in periods (rows)/(energy levels) and groups (columns) properties and trends.

Groups of the periodic table Group 1 Alkali Metals Soft metal – could cut w/ butter knife Highly reactive – all group 1 metals have 1 valence electron Not found in nature as a single element, always found as a compound ( group 1 element bonded to another element) Appears as a shiny gray color

Noble Gases First discovered in 1894 by John William Strutt and Sir. William Ramsay Argon (Ar) was the first Very stable gases located in group 18 on the periodic table

The Lanthanides – 14 elements – from atomic number 58 – 71 The Actinides – 14 elements from atomic number 90 – 103 Periodicity – 1, 8 ,18, 32, 32 When looking at a group on the periodic table the difference between the atomic numbers follows the pattern above. Group 1 – Sodium (Na) atomic is 8 more than Lithium (Li); Potassium (K) is 8 more than Li; Rubidium (Rb) is 18 more than K

Electron Configuration review