Chemical Bonding and Molecular Structure

An element of a pure substance contains only one kind of atom. Molecule is a group of two or more atoms that are chemically bonded together, i.e. tightly held together by attractive forces. Atoms of the same element or different elements can join to form molecules. The same type of atoms constitutes the molecules of an element. A molecule of ozone (O₃) consists of three atoms of oxygen and thus, it is a molecule of an element. Sugar (C₁₂H₂₂O₁₁), sodium chloride (NaCl) and salt (NaCl) consist of atoms of different elements joined together in definite proportions. Thus, they are molecules of compounds.

He has the lowest electronegativity.

H₂ = 2 electrons: s1s² Bond order = ½ (Number of bonding MOs - Number of antibonding MOs) = ½ (2-0) = 1 Diamagnetic due to nil unpaired electrons.

Both NO₃^- and CO₃^2- have 32 electrons with sp² hybridised central atom and trigonal planar geometry.

Central atom has sp³ hybridisation in SiBr₄, ClO₂^-, ClO₃^- and SiC molecules/ ions.

The hybridisation of carbon as central atom in diamond, graphite, ethylene and acetylene is sp³, sp², sp² and sp respectively.

X₂O₃ has sp³ hybridisation, one lone pair and trigonal pyramidal geometry.

H₂ (2 electrons) = s1s² ; diamagnetic He₂²⁺ (2 electrons) = s1s² ; diamagnetic

Helium has the lowest electronegativity because it is a noble gas and noble gases are chemically very stable as they have the maximum number of valence electrons that their outer shell can hold. Thus, the noble gas atom, being electrically neutral, would not be able to exert much attractive force on free-ranging electrons, i.e. low electronegativity.

Na²⁺ is of the smallest size.

Aluminium ion has the largest size than all the other given ions.

The size of anion is always greater than the corresponding atom. Thus, only statement 1 is correct.

A metalloid is a chemical element with properties that are in between a mixture or those of metals and non-metals. It is considered to be difficult to classify unambiguously as either a metal or a non metal. Iron is a metal. So, it does not have the properties of metalloids.

Both As and Sb belong to group b15 and are metalloids, which have the properties of metals as well as non-metals. Metalloids do not form positive ions in chemical reactions. Metals and poor metals both form active positive ions during the chemical reactions.

A co-ordinate bond is a covalent bond (a shared pair of electrons) in which both the electrons of a shared pair come from the same atom.