Section 5.2: Electron Configuration and the Periodic Table
Periods and Blocks of the Periodic Table:
-Elements arranged vertically in groups/family with similar properties
-Elements in horizontal rows (period) w/ similar chemical properties
-Length of period = number of electrons occupying sublevels being filled in that period
-Periodic Table divided into 4 blocks:s,p,d,f
- Name of each block determined by whether an s,p,d, or f sublevel is being filled in successive elements of that block
-Period of element determined from element’s electron configuration
- Aresnic: [Ar]3d104s24p3
- 4 in 4p3 indicates arsenic’shighest occupied energy level is 4
The s-Block Elements: Groups 1 and 2:
-Elements of s block are chemically reactive metals (Grp1 more reactive)
-Outermost energy level in atom of each Grp 1 element contains a single s electron
- Makes Grp1 metals extremely reactive
-N = number of highest occupied energy level
- Grp 1 & 2 elements are ns1 and ns2
- E.g. Na grp configuration written as ns1 where n = 3
-Alkali Metals: elements of Group 1 of periodic table
- In pure state, have silvery appearance and are soft to cut with knife
- So reactive, not found in nature as free elements
- Combine vigorously w/ most nonmetals
- React strongly w/ water ot produce hydrogen gas & alkali solution
- Stored in kerosene because of extreme reactivity w/ air and moisture
- Group 1: lower down column, melt at lower temperatures
-Alkaline-earth metals: elements of Group 2 of the periodic table
- Atoms of alkaline-earth metals contain a pair of electrons in outermost s sublevel
- Group configuration: ns2
- Harder, denser, stronger than alkali metals
- Higher melting points than alkali
- Less reactive, but also too reactive to be free elements
Hydrogen and Helium:
-Hydrogen unique elements, not related to Group 1
-Electron configuration: 1s1 (ns1)
-Though helium has ns2 configuration, its part of Grp 18 since unreactive
The d-Block Elements: Groups 3-12
-Each d sublevel consists of five orbitals with a maximum of two electrons each, or up to 10 electrons possible in each d sublevel
-Group configuration for Group 3: (n-1)d1ns2
- E.g. atoms of Group 12 elements have 10 electrons in the d sublevel plus two electrons in the ns sublevel
- Grp config: (n-1)d10ns2
-Deviations from orderly d sublevel filling occur in grps 4-11
- E.g.: Nickel:
- [Ar]3d84s2
- Sums of outer s and d electrons is equal to group number (3+4=7)
-Transition Elements: d-block elements are metals with typical metallic properties
- good conductors of electricity and have high luster
- less reactive than alkali metals and alkaline-earth
The p-Block elements: Groups 13-18 (except Helium)
-Main-group elements: p-block elements together with the s-block elements
-Electron configuration: ns2np1
-Total number of electrons in highest occupied level = group number minus 10
- i.e.: Bromine: 17-10
-p block properties vary greatly
- right: nonmetal; left: metalloids
-Halogens: elements of group 17
- Most reactive nonmetals
- React with most metals to form salts
-Metalloids mostly brittle solids
-Metals of p block generally harder/denser than s-block alkaline-earth metals, but softer and less dense than the d-block metals
The f-block elements: Lanthanides and Actinides
-Filling of the 4f sublevel
-With seven 4f orbitals to be filled w/ 2electrons each, there are a total of 14 f-block elements
-Lanthanides are shiny metals similar to Grp 2 alkaline-earth metals
-14 f-block elements called actinides
- 5f sublevel is being filled with 14 electrons
- Actinides are all radioactive