Ch 5.2: Electron configuration and the periodic table.

In general terms, the electron configuration of an atom’s highest occupied energy level determines the atom’s chemical properties.

Periods and Groups

Elements are arranged vertically in groups that share similar chemical properties.

Periods and Groups

• Elements are arranged horizontally in periods• the length of each period is determined by

the number of electrons that can occupy the sublevels being filled in that period.

Sublevel Blocks

Based on the electron configuration of the elements, the periodic table can be subdivided into four sublevels, or blocks.

Alkali Metals Group 1 ( ns( ns11))

• Most reactive, soft, silvery metals.

• Stored under kerosene/oil.

• Are not found free in nature, but as compounds - too reactive to exist alone.

• Combine readily with non metals.

• Combine readily with water

• 2 H2O + 2 X → H2 + 2 XOH

• Melting point decreases as you move down the group.

Group configuration

Alkaline Earth metals Group 2 (ns(ns22))

• Similar to group 1, but are harder, denser, stronger, and have higher melting points.• Less reactive than the alkali metals, but

still too reactive to be found free in nature.

Barium in oil.Barium in oil.

Special Cases: H and He

• By electron configuration H is in Group 1, but it does not have the characteristics of an alkali metal.

• By electron configuration He should be in Group 2, but it does not have the chemical characteristics of the group and acts as a noble gas, so it is put in Group 18.

Example #1

•Without looking at the periodic table, give the group, period, and block in which the element with the electron configuration [Xe]6s2 is located.

• Group 2 (ns2)

• Period 6 (6s2)

• Block s (6s2)

Example #2

•Without looking at the periodic table, write the electron configuration for the Group 1 element in the third period.

• 1s22s22p63s1

Example #2

•Which element is likely to be more active:

• [Xe]6s2 or 1s22s22p63s1 ?

• 1s22s22p63s1 because it is in Group 1 (alkali metals)

Example #3

•Without looking at the periodic table, give the group, period, and block in which the element with the electron configuration [Kr]5s1 is located.

• Group 1 (ns1)

• Period 5 (5s1)

• Block s (5s1)

Example #4

•Without looking at the periodic table, write both the group configuration and the complete electron configuration for the Group2 element in the 4th period.

• Group ns2

• 1s22s22p63s23p64s2

Transition metals (d block) Groups 3-12

• Sum of d and s electrons give group number of the element. Ex. Cr = [Ar] 4s13d5 is in group 6.

•Metallic properties (shiny, conduct heat and electricity, ductile, malleable)

• {{nsns22(n-1)d(n-1)dxx}}

Transition Metals

• are less reactive than Groups 1 and 2

• Some are so unreactive that they do not easily form compounds and can exist in nature as free elements (also called native elements).

Native gold

Example #4

• An element has the electron configuration [Kr]5s24d10 Without looking at the periodic table, identify the period, block, and group in which this element is located.

• Period 5 (5s2)

• Block d (5s24d10)

• Group 12 (2+10)

P block elements Group 13-18

• The p-block elements together with the s-block elements are called the main group elements.

• The properties of the elements in the p block vary greatly (mixture of metals, metalloids, non-metals, and the noble gases).

• (ns(ns22npnp1 1 through nsthrough ns22npnp66))

• Group number = ns electrons + np electrons +10

P block elements Group 13-18

•Metalloids: Brittle solids, semiconductors, exhibit properties of both nonmetals and metals.• P-block metals less dense and hard than

d-block metals, but greater than Groups 1 and 2. When pure, are stable in the presence of air.• Noble gases=unreactive. Why????

Group 17 – The Halogens

•Halogens: most reactive nonmetals •React vigorously with

metals, forming salts.• F2 (green gas), Cl2 (yellow

gas), Br2 (red liquid), I2 (purple solid).• (ns2np5)

Group 18 - Noble Gases

• Stable elements, do not normally undergo chemical reactions.

• The stability is a result of electrons filling the highest energy level.

• Helium is 1s2, all the other noble gases are said to have “stable octets” because the configuration is ns2 np6 (8 electrons in outer energy level = octet).

• (ns2np6)

Lanthanides (Rare Earths)

• Shiny, reactive metals.

• Similar in reactivity to the Group 2 alkaline earth metals.

• Electrons fill up f orbitals.

•Atomic # 58-71

Actinides

•All radioactive metals.• First 4 naturally occurring.• The remainder are called

the transuranic elements (“beyond uranium”), and are synthesized•Atomic #90-103

Example #5

• An element has the electron configuration [Ne]3s23p5 Without looking at the periodic table, identify the block, and group in which this element is located.

• Block p (3s23p5)

• Group 17 (2+5+10)

Example #6

• An element has the electron configuration [Ne]3s23p5 What element is this? Is this a metal, nonmetal, or metalloid?

• Chlorine

• Group 17 halogen (non-metal), which means it is very reactive.

Example #6

• An element has the electron configuration [Xe]6s24f6 What element is this? Is this a metal, nonmetal, or metalloid?

• This is an f-block element in the lanthanides (4f). Samarium, Sm.

• Lanthanides are reactive metals.

Assignment – Due tomorrow

• 5.2 Worksheet

Yee-hah!!!