Periodic Table What is it, and how is it useful?

Periodic Table An overall arrangement of elements by increasing atomic number, a vertical arrangement by number of valence electrons, and a horizontal arrangement by number of energy levels.

History - Mendeleev In 1869 he published a table of the elements organized by increasing atomic mass. He was so confident in his table that he used it to predict the physical properties of three elements that were yet unknown. However, in spite of Mendeleev’s great achievement, problems arose when new elements were discovered and more accurate atomic weights determined.

History - Mosley In 1913, through his work with X-rays, he determined the actual nuclear charge (atomic number) of the elements. He rearranged the elements in order of increasing atomic number. His research was halted when the British government sent him to serve as a foot soldier in WWI. He was killed in the fighting in Gallipoli by a sniper’s bullet, at the age of 28. Because of this loss, the British government later restricted its scientists to noncombatant duties during WWII.

Periodic Law States that the physical and chemical properties of elements are periodic functions of their atomic numbers.

More details…. The individual boxes within the table generally give the element’s name, symbol, atomic number, and atomic mass.

Group A vertical arrangement of elements by number of valence electrons. The groups are numbered 1-18

Group (cont) The LAST DIGIT of the groups 1, 2, and tells you how many valence electrons the elements in the group have. So all elements in group 1 have 1 valence electron All elements in group 15 have 5 valence electrons

Group Names Certain groups have special names assigned to them.

Group Names (cont) Group 1 - Alkali Metals Group 2 – Alkaline Earth Metals Group 3-12 – Transition metals Group 17 – Halogens Group 18 – Noble Gases

Yes, you have to memorize the group numbers and names.

Periods Horizontal arrangement of elements by number of energy levels. Numbered 1-7 and the period number tells how many energy levels each element has. Also tells which energy level is the valence

Metals VS Non-Metals Every element to the left of the staircase line is a metal (EXCEPT HYDROGEN) Every element to the right of the staircase line is a non-metal Hydrogen is a NON-METAL (exception to the rule)

Properties of Metals Shiny (luster) Malleable (pounded into thin sheets) Ductile (made into wire) Good conductors (of heat and electricity)

Metalloids Elements that are found along the staircase line Have properties of both metals and non-metals Must touch the staircase line to be a metalloid

Reactivity Elements become more reactive as you move from top to bottom on the periodic table. The alkali metals are the more reactive group of elements on the periodic table.

Size of Atoms As you move left to right on a row, the elements become smaller (due to increasing pull on the electrons) As you move top to bottom in a group, the elements become larger. Each additional energy level causes a large increase in size.