Question

Explain the reason for the unexpected values of the first ionization energies of the group 3A and group 6A elements, relating the apparent decrease from the previous group in terms of the orbital electron configuration. Explain how ionization energy relates to electronegativity, and explain that property. Be sure to define the two properties, and discuss their trends the relationship between each property and the size of atomic shells, as well as the reason for the numeric difference in electronegativity, both down and across a period

Explain the historical context of oxidation and reduction processes, and describe our current understanding of the nature of oxidation and reduction, and how they function in a reaction.

Compare and contrast the terms “mixture” and “compound”. Your answer should be more in depth than just defining the two term

Answer 1

Ionisation energy is the energy required to remove one electron from a gaseous atom or ion. Ionisation energy increases along a period as the size of electronic shell/ atomic radius decreases across the period. The effective nuclear charge felt by the outer electron is more as we move across the period. But, it decreases down a group because when we move down a group, the atomic radii of the elements increases.

There is an unexpected value of first IE (ionisation energy) in group 3A. This is because, in group 3, the outermost electron is in p-orbital. While group 2, the outermost electron is in s-orbital. For example, Boron, B has an electronic configuration - 1s²,2s²,2p¹. The p-orbital is far away from the nucleus than s- orbital. Therefore, less energy is required to expel the electron from p-orbital.

The unexpected value in 6A elements due to the spin of electrons. According to Hund's rule and Pauli's exclusion principle, two electrons with opposite spin occupy the first p-orbit and two different electrons with the same spin occupy the subsequent p-orbitals. The two electrons in the first p-orbital repel each other, so it is easier to remove one of them and the atom attains a stable half filled configuration.

Electronegativity and ionisation energy are closely related.

Electronegativity is the tendency of an atom to attract electrons towards itself. Electronegativity increases across a period as the size of atom decreases. This is due to the strong pull of electrons by the positively charged nucleus as the size decreases along a group. But, decreases while moving down a group as the size of the atoms increases. The electrons will be away from the nucleus as the size of atomic orbital increases down the group. Hence they will feel relatively less attraction from the nucleus.

The greater affinity for electrons, the greater is the ionisation energy. So the atoms with higher electronegativity will have higher ionisation energy.

Oxidation and Reduction

Historically, oxidation just meant the addition of oxygen and reduction was defined as removal of oxygen.

In the current scenario, oxidation is the loss of electrons or an increase in oxidation number of a molecule, atom or ion. While the reduction is gaining electrons or decrease in the oxidation number of a molecule, an atom or ion.

Redox reactions occur when there is a transfer of electrons from one species to another. The species that lose electrons and get oxidised are termed as reducing agents. Similarly, the species that gain electrons and get reduced are called oxidising agents.

Mixture and compounds

Property	Compound	Mixture
Meaning	Compound is formed by chemical reaction of two elements	Intermingling of two substances physically
Nature	Homogeneous	Homogeneous or heterogeneous
Compisition	Fixed	Varying
Substance	pure	impure
Properties	constituents lose their properties	constituents retain their properties
New product	Formation of new product occurs	No formation of new products
Separation	chemical methods	physical methods
Melting and boiling point	Defined	Not defined