Below are the elements of the Short Period Table; those with s- and p- valence electrons. The Transition elements and the Lanthanides are not included.
|
Name of element First Ionisation Potential (or Electron Affinity) in KJ/mol, Ionic radius in Armstrong, Electronegativity |
So for beryllium (Be) the first ionisation potential = 899 kJ/mol, ionic radius (Be+) = 0.27�, and electronegativity = 1.5.
| 1s | H 1312 (72.8), - 2.2 | ||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| 2s, 2p | Li 513 0.59 - |
Be 899 0.27 1.5 |
B 801 0.12 2.0 |
C 1086 - 2.5 |
N (-7) 1.71 3.1 |
O (141) 1.40 3.5 |
F (322) 1.33 4.1 |
Ne | |||
| 3s, 3p | Na 496 1.02 - |
Mg 738 0.72 1.2 |
Al 577 53 1.5 |
Si 786 - 1.7 |
P 1012 212 2.1 |
S (200) 184 2.4 |
Cl (349) 181 2.8 |
Ar | |||
| 4s, 3d, 4p | K 419 1.38 - |
Ca 579 1.00 - |
Transition elements |
Ga 579 62 1.8 |
Ge 762 2.0 |
As 947 2.22 2.2 |
Se (195) 1.98 2.5 |
Br (324) 1.96 2.7 |
Kr | ||
| 5s, 4d, 5p | Rb 403 1.49 - |
Sr 550 1.16 - |
In 558 0.79 1.5 |
Sn 709 - 1.7 |
Sb 834 - 1.8 |
Te (190) 2.21 2.0 |
I (295) 2.20 2.2 |
Xe | |||
| 6s, 4f, 5d, 6p | Cs 375 1.67 - |
Ba 503 1.36 - |
Lanthanides | Transition elements |
Tl 589 0.88 1.4 |
Pb 715 - 1.6 |
Bi 703 - 1.7 |
Po | At | Rn | |
Our interest here is what compounds - ionic or covalent - are formed by the elements in the Short Period. We will use the following colour code.
| Cationic | Cationic or Covalence | Covalence | Covalence or Anionic | Cationic or Covalence or Anionic |
|---|
By cationic or anionic we mean the ions does exist in solution. So the cationic can react with the anionic to give ionic compounds, and those that are covalence can form covalent compound. There are two factors which will decide whether the element can form an ion or to take part in covalent bonding. The ionisation potential (or the electron affinity) and the ionic radius.
Let us consider lithium. A first ionisation potential of about 500 kJ/mol is low enough for the formation of a cation. However an ionic size of 0.59 A is considered small resulting in an intense surface charge density (charge per unit surface area). So the cation formed is attracted very strongly to any anion present in the system (In nature all systems are neutral) to form a weak covalent bond. However with certain anion it is still possible to get Li+. So Li is classified as cationic or covalent.
The size of the Be+� and B+� ions are even smaller than Li+ and the charge is +2 and +3 respectively, instead of +1. So Be and B form covalent compounds only.
Now let us take a look at the elements in the right hand top quarter of the Table. They have high electron affinity so they can form anions. For anion the ionic radius is not so significant since they are all fairly large. They can then form ionic compounds with cations. That means the Group IA and Group IIA elements. With other elements it can only form covalent compounds.
With this paradigm it should be easy for us to discuss the chemistry of the elements in the Short Period. It is very important that the trend display in this Short Period is not rigid and should only be used as a guard.
| HYDROGEN || Group IA | Group IIA | Group IIIB | Group IVB | Group VB | Group VIB | Group VIIB |
| CONTENT |
