Test: Chemical Bonding - UPSC MCQ

Ionization energy is the energy required to remove an electron from a gaseous atom or ion. As we move from left to right in a period, the number of protons in the nucleus increases, which leads to a stronger pull on the electrons. Therefore, more energy is required to remove an electron from an atom, which means the ionization energy increases. Furthermore, the atomic radius decreases across a period, which means the electrons are closer to the nucleus and more tightly bound to it, further increasing the ionization energy. Hence, the ionization energy generally increases from left to right in a period.

p orbitals can form both sigma (σ) and pi (π) bonds.
A sigma bond is the strongest type of covalent bond, in which the atomic orbitals directly overlap between the nuclei of two atoms. This can happen with two p orbitals, or between an s orbital and a p orbital.
A pi bond is a type of covalent bond that exists between atoms where the electrons are on top and bottom of the axis connecting the nuclei of the joined atoms. This bond is formed by the side-on overlapping of p orbitals.
So both σ and π bonds can be formed by the overlap of p orbitals.

Copper is a metal and metals do not form covalent bonds. They form metallic bonds which involve the sharing of free electrons among a lattice of positively charged ions. On the other hand, Ice, Diamond, and Graphite are all made up of non-metals, and non-metals form covalent bonds by sharing electrons. Therefore, the solid that does not contain a covalent bond is Copper.

The shielding effect remains constant across a period in the periodic table. This is because electrons are being added to the same energy level. Even though the number of electrons increases, they are roughly the same distance from the nucleus and do not shield each other effectively from the increasing nuclear charge. Therefore, the shielding effect remains constant.

The number of unpaired electrons is determined by the electron configuration of an atom, specifically the number of electrons in the outermost orbitals (also known as valence electrons). In the periodic table, elements are arranged in order of increasing atomic number. The atomic number corresponds to the number of protons in an atom and, in a neutral atom, also the number of electrons.

Without further information on what elements X, Y, Z, and W represent, it's impossible to provide a specific explanation. However, if we assume that the numbers before each letter represent the atomic number of the elements, then 7Y would represent Nitrogen, which has 5 electrons in its outer shell, 3 of which are unpaired. This is more than elements with atomic numbers 6, 9, and 13 (Carbon, Fluorine, and Aluminum, respectively), which have fewer unpaired electrons in their outer shells.

Therefore, if the numbers before each letter represent the atomic numbers of the elements, then 7Y (Nitrogen) would have the maximum number of unpaired electrons.

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. It is used to predict the nature of chemical bonding in a molecule or compound. The more electronegative an atom is, the more it attracts electrons towards it. This concept was introduced by Linus Pauling.

Option A, Ionization energy, is the amount of energy required to remove an electron from a gaseous atom or ion.

Option B, Electron affinity, is the energy change that occurs when an electron is added to a gaseous atom.

So, an atom's relative attraction for the electrons in a chemical bond is best described by its electronegativity, not its ionization energy or electron affinity.

Electron affinity is the energy change that occurs when an electron is added to a neutral atom. In general, electron affinity increases from left to right across the periodic table and decreases down a group.

Although Fluorine (F) is more electronegative, it has a smaller atomic radius than Chlorine (Cl), meaning that any added electron would be closer to the nucleus and more strongly attracted to it. But, the size of the 2p orbitals in Fluorine is so small that it results in electron-electron repulsion. This makes it hard for Fluorine to accommodate an extra electron.

On the other hand, Chlorine (Cl) has a larger atomic radius and its 3p orbitals are larger than the 2p orbitals of Fluorine, which reduces the electron-electron repulsion. Therefore, Chlorine can accommodate an extra electron more comfortably than Fluorine.

This makes Chlorine (Cl) have a higher electron affinity than Fluorine (F), Bromine (Br), and Iodine (I). So, the correct answer is Chlorine (Cl).

The octet rule states that atoms tend to combine in such a way that they each have eight electrons in their valence shells, giving them the same electronic configuration as a noble gas.

Phosphorus (P) is an exception to the octet rule. It can expand its valence shell to hold more than eight electrons. This is possible because phosphorus (as well as sulfur and chlorine) has empty d orbitals in the third energy level that can accept extra electrons. Therefore, phosphorus can form compounds where it is surrounded by more than eight electrons, such as PCl5 (Phosphorus pentachloride), which does not follow the octet rule. So, the correct answer is D. P (Phosphorus).

CO₂ is a non-polar molecule primarily because the dipole moment is zero.
In a molecule, a dipole moment is formed when there is a difference in electronegativity between the atoms. This causes a charge imbalance and creates a dipole (two poles, one positive and one negative). In CO₂, the molecule is linear with the oxygen atoms on either side of the carbon atom. While oxygen is more electronegative than carbon, causing each C-O bond to be polar, the linear shape of the molecule ensures that the individual bond dipoles cancel each other out.
Because the molecule is symmetrical, the dipoles on either side of the carbon atom are equal in magnitude but opposite in direction. As a result, the net dipole moment of the entire molecule is zero, making it non-polar.
So, while the linear geometry (option A) and Sp hybridization (option C) contribute to the overall characteristics of CO₂, the best explanation for its non-polarity is the zero dipole moment (option B).

Electronegativity is not an absolute term of the element because it does not refer to a single, independent property of an atom itself, but rather a comparative measure of how strongly an atom in a molecule attracts shared electrons towards itself. It is a relative value, often measured on the Pauling scale, and varies depending on the environment the atom is in and the other atoms it is interacting with. Thus, it is not an inherent, absolute property of the atom in the same way that ionization energy, electron affinity, or atomic size are.