S Block Elements and Their Properties


S Block Elements Periodic Table
The S block elements have valence electrons in the s orbital.

The s block elements are a group of chemical elements that have valence electrons in the s-subshell. In other words, atoms of these elements have a general valence electron configuration of ns1-2, where “n” is the principal quantum number and “s” is the orbital. A maximum of The elements are those in group 1 (the alkali metals), group 2 (the alkaline earth metals), and helium. French scientist and engineer Charles Janet introduced the concept of element blocks and also arranged the elements into different periodic table designs according to blocks.

List of S Block Elements

There are 14 s-block elements:

  • Hydrogen (H)
  • Helium (He)
  • Lithium (Li)
  • Beryllium (Be)
  • Sodium (Na)
  • Magnesium (Mg)
  • Potassium (K)
  • Calcium (Ca)
  • Rubidium (Rb)
  • Strontium (Sr)
  • Cesium (Cs)
  • Barium (Ba)
  • Francium (Fr)
  • Radium (Ra)

Note that helium is in the same column as the p-block elements, but it does not have any valence electrons in the p subshell.

Electron Configurations

The alkali metals have a single valence electron in their outer shell, while helium and the alkaline earth metals have two valence electrons in the outer shell. Here is a list of the s-block element electron configurations:

Atomic NumberSymbolElectron Configuration
1H1s1
2He1s2
3Li1s22s1
4Be[He]2s2
11Na1s22s22p63s1
12Mg[Ne]3s2
19K1s22s22p63s23p64s1
20Ca[Ar]4s2
37Rb1s22s22p63s23p63d104s24p65s1
38Sr[Kr]5s2
55Cs[Xe]6s1
56Ba[Xe]6s2
87Fr[Rn]7s1
88Ra[Rn]7s2

Properties of the S Block Elements

All of the s-block elements, except helium, readily lose their valence electrons and form chemical bonds. The elements in group 1 form ions with a +1 charge, while those in group 2 form ions with a +2 charge. With the exceptions of hydrogen and helium, the s-block elements are highly reactive metals. The metallic elements are shiny, silver-colored (except cesium, which has a golden tint), and good electrical and thermal conductors. The s-block elements form soft, light solids that have low melting points. Except for hydrogen and helium, the elements vigorously react in air and in water. Keeping them in an inert atmosphere or under mineral oil protects them against oxidation.

The Diagonal Relationship

The diagonal relationship is when an element display behavior more like the element diagonal to it on the periodic table than to other elements in its own group. This occurs in some s-block elements. Lithium displays behavior similar to magnesium. Beryllium acts similarly to aluminum. The reason for this behavior is because lithium/magnesium and beryllium/aluminum are element pairs with similar ionic radius sizes and comparable charge/radius ratios.

Identifying S Block Elements

The s-block elements feature prominently in firework colors. So, the flame test is a good first step toward identifying them. Note that not all of these elements display a characteristic color and some colors are similar to each other.

ElementFlame Test Color
LithiumCarmine red
SodiumYellow
PotassiumLilac
RubidiumViolet red
CesiumBlue violet
BerylliumWhite
MagnesiumColorless to white
CalciumBrick red
StrontiumCrimson red
BariumApple green

Aside from the flame test, the reactivity series helps identify an element when comparing its reactivity against another. For example, lithium replaces other metals in a reaction. Barium replaces calcium or magnesium, but not lithium.

References

  • Gschneidner Jr., Karl A. (2016). “282. Systematics”. In Jean-Claude G. Bünzli; Vitalij K. Pecharsky (eds.). Handbook on the Physics and Chemistry of Rare Earths. 50. ISBN: 978-0-444-63851-9.
  • Langmuir, Irving (June 1919). “The Arrangement of Electrons in Atoms and Molecules”. Journal of the American Chemical Society. 41 (6): 868–934. doi:10.1021/ja02227a002
  • Scerri, Eric (2020). “Recent attempts to change the periodic table”. Philosophical Transactions of the Royal Society A. 378 (2180). doi:10.1098/rsta.2019.0300
  • Stewart, Philip (April 2010). “Charles Janet: unrecognized genius of the Periodic System”. Foundations of Chemistry. 12: 5–15. doi:10.1007/s10698-008-9062-5