Unit 2:Periodicity & the Periodic

Table

I. HistoryA. Dmitri Mendeleev –

• first person to organize elements based on atomic mass• left gaps for elements not discovered yet

B. Due to isotopes and other information, the modern table is arranged by order of increasing atomic number

II. Types of ElementsA. Metals –

• left of stair step line• 85% of elements• tend to lose electrons• shiny (lustrous) – but can tarnish if react

with oxygen• ductile – shaped into a wire• malleable – hammered into sheets • good conductors of heat & electricity

B. Non-metals –• right of stair step line (except Hydrogen)• tend to gain electrons• brittle• poor conductors of heat & electricity• can be solid or gas, only 1 liquid

C. Metalloids – • 7 elements around stair step line• B, Si, Ge, As, Sb, Te & Po (At excluded due to

radioactivity)• exhibit properties of both metals & non-metals

III. Regions of Tablegroups (families) – columns (1-18)

periods – rows (1-7)

A. Main Group (Representative) Elements-• Groups of elements in the “s” & “p”

blocks of the table

• Hydrogen- doesn’t belong to any group found above group 1, although it is

not a metal chemically behaves more like group 1

elements

• Groups with special names1. Alkali metals - group 1

- most reactive metals - video

- 1 valence electron (ns1)

2. Alkaline Earth Metals – group 2- less reactive than group 1- 2 valence electrons (ns2)

3. Chalcogens – group 16 (or 6A)- 6 valence electrons (ns2p4)

4. Halogens – group 17 (or 7A)- most reactive non-metals- 7 valence electrons (ns2p5)

5. Noble Gases - group 18 (8A)- non-reactive non-metals

- 8 valence electrons (ns2p6)

*except He = 2 valence electrons

B. Transition Metals – • metals in the “d” block of table• have 1 or 2 valence electrons in “s”

orbital• range in reactivity

C. Inner Transition Metals-• in “f” block of table• referred to as series

Lanthanide Series – first row of “f” blockall are metalsActinide Series – second row of “f” blockmost are radioactive & man-made

(synthetic)