History of the Periodic Table Chemistry I

Bell Work It’s always a good idea to have organization in your life. What are some things you keep organized to make life easier?

Dmitri Mendeleev Him and Lother Meyer first identified a way for classifying the elements in 1869 Mendeleev published his scheme first and was more successful at demonstrating its value, so he is given more credit Noticed when organizing elements by increasing atomic mass, he could see a periodic repetition of their properties

Dmitri Mendeleev Mendeleev sometimes broke the pattern of organizing them by atomic mass so elements of similar properties can be kept in the same columns Predicted a new element – ekasilicon that had very similar properties to the later discovered germanium!

Henry Moseley In 1913, Moseley reorganized atoms by atomic number This kept all elements organized by properties, but deals with the few inconsistencies where mass number didn’t increase along with atomic number Periodic Law – when elements are arranged in order of increasing atomic number, their physical and chemical properties show a periodic pattern

GROUPS AND PERIODS Group – column down a periodic table, also called families Period – horizontal rows in the periodic table Groups normally referred to as 1A -8A, skipping over the transition metals Transition metals are 1B to 8B Numbered 1-18 also

Groups (Columns) of the Periodic Table Alkali metals – group 1 Very reactive Alkaline earth metals – group 2 Slightly less reactive Halogens – group 17 Often react with alkali metals to form salts Noble Gases – Group 18 Very unreactive gases

Periodic Table

s, p, d, and f block elements s-block elements Groups 1 and 2 Metals Electron configurations all end in s p-block elements Groups 13-18 Contain metals, nonmetals, and metalloids Electron configurations all end in p d-block elements Transition metals All end in d f-block elements Lanthanides and actinides All end in f

Valence Electrons Core Electrons – “inner” electrons, do not participate in bonding Valence Electrons – “outer” electrons, electrons in the highest occupied energy level number of valence electrons largely determines the chemical properties of an element So which electrons in an electron configuration are core and valence? Be – [He] 2s2 P – [Ne] 3s2 3p3 Core Valence Core Valence

So how do I find this valence number? The valence electrons an atom has is the same as its group number for a representative (main group) element

So how do I find this valence number? So how many valence electrons would Na have? 1 Iodine? 7 Krypton? 8