Introduction of group-16 and group-17 elements and their properties
In today’s article, we will learn about the key points i.e. important points related to the group-16 and group-17 elements of p-block in the periodic table.
These points can help us remember the basics of group-16 and group-17 element’s properties in an easy way. So let’s start point by point.
Key points of group-16 elements
- Elements O, S, Se, Te and Po constitute group-16 of the periodic table. ns^2np^4 are the general valence shell electronic configuration.
- Atomic and ionic radii increase down the group while ionisation enthalpy and electronegativity decrease with increase in atomic number.
- It has less negative electron gain enthalpy comparison with sulphur because of the compact nature of oxygen atom. However, from sulphur onwards, the value again becomes less negative to polonium, Po.
- Group-16 elements show a number of oxidation states. Oxygen shows only negative oxidation state except in case of OF2(+2) and O2F2(+1). Other elements of this group exhibit +2, +4, +6 oxidation states but +4 and +6 are common. The stability of +6 oxidation state decreases and +4 oxidation state increases down the group reason being the presence of inert pair effect.
- H2M type hydrides are formed by all types of elements. Acidic character and reducing character hydrides increases from H2S to H2Te. Bond dissociation enthalpy, thermal stability and HMH angle decrease down the group. Boiling points increases from H2S to H2Te. H2O has extraordinarily high boiling point due to intermolecular H-bonding. H2O does not produce reducing property.
- MO2 and MO3 type oxides are formed by these elements. SO2 is reducing while Tio2 is an oxidising agent. Both types of oxides are acidic in nature.
Important information about group 16 elements
- MX2, MX4 and MX6 type halides(X=F, Cl, Br and I) are formed by these elements. All hexafluorides are gaseous and octahedral in shape. SF6 is exceptionally stable for steric reasons. MX4(SF4, Se4 etc.) type halides have sp3d hybridization and have a trigonal bipyramidal structure in which one of the equatorial positions is occupied by a lone pair of electrons(see-saw geometry). Dihalides are sp^3 hybridized and have a tetrahedral shape.
- Sulphur in the vapour state(S2) and dioxygen(O2) are paramagnetic in nature.
- Ozone is an allotropic form of oxygen. Due to the ease with which it liberates atoms nascent oxygen, it acts as a powerful oxidizing agent.
- The two oxygen-oxygen bond lengths in the O2 molecule is identical and the molecule is angular.
- Both rhombic and monoclinic sulphur have S8 molecules. The S8 ring in both the forms is puckered and has a crown shape. In cycle S6, the ring adopts the chair form.
- SO2 is produced as a by-product of the roasting of sulphur ores. It behaves as a reducing agent(when moist). The two S-O bonds in the SO2 molecule are equal due to two resonating structures. The SO2 molecule is angular.
- Sulphuric acid is manufactured by the contact process. It forms two series of salts; normal sulphates and acid sulphates. The large value of Ka^+ indicates that H2SO4 is largely dissociated into H^+ and HSO4^- ions. Greater the value of Ka, the stronger is the acid.
Concentrated H2SO4 acts as a strong dehydrating agent. it removes water even from organic compounds.
Key points of group-17 elements
- F, Cl, Br, I and At(astatine) are the elements of group 17. These are collectively known as halogens. It is a radioactive element. Their general valence shell configuration is ns^2np^5.
- Halogens have smallest atomic radii in their respective periods due to maximum effective nuclear charge. Atomic and ionic radii increase from fluorine to iodine.
- Halogens have very high ionization enthalpy because they have very little tendency to lose an electron.
- Halogens have maximum negative electron gain enthalpy in the corresponding periods because they have only one electron less than stable noble gas configurations. On moving down the group, it becomes less negative. However, negative electron gain enthalpy of fluorine is less than that of chlorine. It is due to the small size of the fluorine atom. As a result of this, there are strong interelectronic repulsions and the incoming electron(in 2p- orbital) does not experience much attraction.
- The reason of halogens being coloured is due to absorption of radiations in visible region which results in excitation of valence shell electrons to higher energy level.
- Smaller dissociation enthalpy of F2 in comparison to Cl2 shows that there is relatively large electron-electron repulsion between the lone pairs in an F2 molecule due to its small size.
- All halogens exhibit -1 oxidation state. However, Cl, Br, I exhibit +1, +3, +5 and oxidation state also. F exhibits only -1 oxidation state because it has no vacant d-orbitals in its valence shell.
So, here we conclude this article I hope you all will get the required knowledge from this one.
Now, you can tell the key elements of group-16 and group-17 elements and also a difference between the group-16 and group-17 elements of p-block elements.
Your comments and suggestions are invited.