Question

Account for the following statements:
A. Helium is used in a diving purpose
B. Fluorine does not exhibit positive oxidation state
C. Oxygen shows catenation behavior less than sulfur.

Answer 1

Hint:The long-form periodic table is based upon the atomic number which is the most fundamental property of an element. The physical and the chemical properties of an element depend upon the distribution of electrons in the valence shell of the atom.

Step-by-step explanation:
Step 1
Helium is the first member of the Group 18 elements. It is a monatomic gas and having a duplet electronic configuration is devoid of any chemical reactivity under ordinary conditions. As all the elements present in this group have a stable valence shell electronic configuration of either a duplet or an octet they are collectively known as inert gas or a noble gas.
There are several uses of noble gases. One of them is helium mixed with oxygen and is used for diving purposes. A mixture of helium and oxygen is used for the respiration of deep-sea divers instead of air because of the less solubility of helium in the blood than nitrogen under high pressure present in the depth of the sea.
Step 2
Fluorine exhibits only the oxidation state of \[ - 1\] in all its compounds. The other halogens exhibit \[ - 1, + 1, + 3, + 5,and + 7\] oxidation states in their compounds. Fluorine, being the most electronegative, can gain an electron. Moreover, as it does not have any vacant d orbital in its valence shell so it is unable to excite its ns or np electron pairs. Thus, fluorine is unable to show higher positive oxidation states.
Step 3
Oxygen, the first member of Group 16 has smaller size as compared to sulfur. Thus the lone pairs of electrons present on the valence shell of the atom are concentrated over a small space and can repel the \[O - O\]bond pair electrons, which is seen as less sulfur due to a bigger size. So, oxygen shows little tendency towards catenation. For example, it links with two atoms in peroxides. Sulfur naturally exists as \[{S_8}\] molecule and shows a greater tendency towards catenation and links up with several atoms in a chain.

Note: The second-period elements show a lot of variation than the other members of the same group due to their small size and greater value of electronegativity.