Periodic Law Chapter 6

In 1863 there were 56 known elements with elements being discovered at a rate of one per year.

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.

Certain similarities in the elements began to appear at regular intervals (periods). In 1869, Dmitri Mendeleev publishes a list of elements. This is the first periodic table

Dmitri Mendeleev

Dmitri Mendeleev 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.

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 with similar properties fall in the same column or group. Periodic Table arranged in periods (rows)/(energy levels) and groups (columns)

Periodicity Periodicity is the difference between atomic numbers of elements in different periods.

Li 8 difference in atomic numbers K Rb 18 Cs 18 Fr 32 periodicity

Periodic Table Group Properties

groups 1 2 13 14 15 16 17 18

S Block elements (groups 1 and 2) The elements in S blocks are reactive metals This means: because the S block elements contain 1or 2 electrons in their highest occupied energy level the element can “lose” that electron very easily and form compounds with other elements S Block elements (groups 1 and 2)

special case classification Hydrogen (H) does not share the same properties as group 1 elements, even though it has only 1 electron in the s orbital. Hydrogen has it’s own unique properties Hydrogen

Alkali Metals (group 1) Group 1 elements are Alkali metals. Alkali metals – all in this group are silvery in appearance and soft enough to cut with a knife, and melt at lower temperatures. Because they are very reactive alkali metals will combine easily with other elements and are not found in nature as free elements. Contain 1 electron in the highest energy level ( 1 valence electron) Alkali Metals (group 1)

Alkaline-Earth Metals ( group 2 ) Highly reactive Group 2 metals are harder, denser, stronger, and have a higher melting point than alkali metals. Contain 2 electrons in highest occupied energy level. ( 2 valence electrons) Alkaline-Earth Metals ( group 2 )

Alkaline-Earth Metals ( group 2 ) These metals are also reactive but not as much as the alkali metals (group 1) Alkaline-Earth metals are too reactive to be found in nature as free elements. Alkaline-Earth Metals ( group 2 )

Helium (He) does not share the same properties as group two but does have 2 electrons in the s orbital. Helium does have the same properties as the other noble gases and is shown in group 18 on most periodic tables. Helium

The P block elements (groups 13-18) Electrons add to the P sublevel only after the S sublevels are filled. The P block elements with the S block elements are called the MAIN-GROUP ELEMENTS. The P block elements (groups 13-18)

For atoms in the P block elements, the total number of electrons in the highest occupied level is equal to the group number minus 10. For example: Br is in group 17, 17 – 10 = 7 electrons in its highest energy level. P block continued

P block continued Halogens – elements in group 17 Halogens are the most reactive nonmetals. React vigorously with metals to form salt compounds. Their reactivity is based on having 7 electrons in the highest energy level P block continued

Metals of P block Harder and denser than the s block alkaline-earth metals, but softer and less dense than d block metals. Can be found in nature as compounds. When obtained as a free metal they are stable in the presence of air.

Metalloids

Metalloids means “metal like” Semiconducting elements Mostly brittle solids with some properties of metals and some properties of nonmetals. Metalloids can conduct heat and electricity but not as well as metals

Good conductors of electricity and have a high luster(shine) Less reactive than alkali metals, and alkaline-earth metals Exist in nature as free elements Palladium, platinum and gold are among the least reactive of all the elements D block elements

Lanthanides and Actinides Lanthanides are shiny metals similar in reactivity to the group 2 alkaline-earth metals Actinides are all radioactive. The 1st four have been found in nature, the remaining are known only as laboratory made element (man made) Lanthanides and Actinides