Question

Consider the collection of nonmetallic elements: \(\mathrm{B}\), As, O, and I. (a) Which two would form the most polar single bond? (b) Which two would form the longest single bond? (c) Which one would be likely to form a compound of formula XY \(_{3} ?(\mathbf{d})\) Which element would likely to participate in two covalent bonds?

Short answer

(a) The most polar single bond would form between B (Boron) and O (Oxygen) as they have the highest difference in electronegativity (1.4). (b) The longest single bond would form between As (Arsenic) and I (Iodine), with a total atomic size of 254 pm. (c) Boron (B) would be likely to form a compound of the formula XY3, as it has 3 valence electrons. (d) Oxygen (O) is the element most likely to participate in two covalent bonds, as it has 6 valence electrons, and hence has two lone pairs of electrons available for sharing in covalent bonds.

Step-by-step solution

Determine electronegativity values

First, we need to find the electronegativity values for B, As, O, and I. Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons. We can use a periodic table or electronegativity chart to find these values. Here they are: - B (Boron): 2.04 - As (Arsenic): 2.18 - O (Oxygen): 3.44 - I (Iodine): 2.66

Determine atomic sizes

Next, we'll determine the atomic sizes of the given elements by looking at their atomic radius. The atomic size generally decreases as we move across a period and increases as we go down a group in the periodic table: - B (Boron): 87 pm (picometers) - As (Arsenic): 114 pm - O (Oxygen): 66 pm - I (Iodine): 140 pm

(a) Most polar single bond

In order to determine which two elements would form the most polar single bond, we need to find the pair with the highest difference in electronegativity. The higher the difference, the more polar the bond will be: 1. B-O: \(|2.04 - 3.44| = 1.4\) 2. B-I: \(|2.04 - 2.66| = 0.62\) 3. As-O: \(|2.18 - 3.44| = 1.26\) 4. As-I: \(|2.18 - 2.66| = 0.48\) The highest difference is between Boron (B) and Oxygen (O), with a difference of 1.4. Answer: (a) The most polar single bond would form between B and O.

(b) Longest single bond

To find which two elements would form the longest single bond, we should look for the pair with the largest atomic sizes: 1. B-As: \(87 + 114 = 201\) pm 2. B-I: \(87 + 140 = 227\) pm 3. As-O: \(114 + 66 = 180\) pm 4. As-I: \(114 + 140 = 254\) pm The largest sum of atomic radii is between As (Arsenic) and I (Iodine), with a total of 254 pm. Answer: (b) The longest single bond would form between As and I.

(c) Compound of formula XY3

In order to determine which element is most likely to form a compound with the formula XY\(_3\), it's essential to consider their valence electrons and group in the periodic table: - B (Boron): Group 13, 3 valence electrons - As (Arsenic): Group 15, 5 valence electrons - O (Oxygen): Group 16, 6 valence electrons - I (Iodine): Group 17, 7 valence electrons Boron (B) has 3 valence electrons, which means it can form three bonds with other elements to achieve a stable electron configuration. Answer: (c) Boron (B) would be likely to form a compound of the formula XY3.

(d) Element likely to participate in two covalent bonds

To find the element most likely to participate in two covalent bonds, we need to identify which element can share two of its valence electrons: - B (Boron): 3 valence electrons - As (Arsenic): 5 valence electrons - O (Oxygen): 6 valence electrons - I (Iodine): 7 valence electrons Oxygen (O) has 6 valence electrons, which means it has two lone pairs of electrons available for sharing in covalent bonds. Answer: (d) Oxygen (O) is the element most likely to participate in two covalent bonds.

Key concepts

Electronegativity

The concept of electronegativity is central to understanding chemical bonding. Electronegativity refers to the ability of an atom to attract shared electrons in a chemical bond. This property is instrumental in determining how electrons are distributed in a bond and thus affects the bonding type and bond polarity.
When atoms with different electronegativities bond, they do not share electrons equally. This unequal sharing results in a bond with partial negative and positive charges, known as a polar bond. Higher electronegativity values indicate a stronger attraction for electrons. For instance, oxygen's electronegativity is 3.44, which is significantly more than boron's 2.04, making B-O bonds very polar. Understanding these differences is essential when predicting bond behavior in compounds.

Atomic Radius

The atomic radius is a measure of the size of an atom, typically the distance from the nucleus to the outer boundary of the surrounding electrons.
It influences the length of bonds an atom can form with other atoms. Generally, within the periodic table, atomic radius increases down a group due to additional electron shells and decreases across a period due to increased nuclear charge pulling electrons closer.
In our exercise, arsenic (As) and iodine (I) are noted for forming the longest bond at 254 picometers, attributed to their relatively large atomic radii at 114 pm and 140 pm respectively. Such knowledge guides predictions about molecular size and spatial structure in molecular chemistry.

Valence Electrons

Valence electrons are the outermost electrons of an atom and are crucial in determining an atom's ability to bond with others. These electrons participate in forming bonds and are key to the chemical properties of elements.
Elements in the same group in the periodic table have the same number of valence electrons, which confers similar bonding capabilities. For example, boron in Group 13 has 3 valence electrons, allowing it to form three bonds, such as in a compound formula XY 3. Understanding how valence electrons interact helps predict compound formation and reactivity.

Polar Bond

Polar bonds occur when there is an uneven distribution of electrical charge across a bond, due to differences in electronegativity between the bonded atoms. In a polar bond, electrons are drawn more towards the more electronegative atom, creating partial positive and negative charges at each end of the bond.
This concept is essential for understanding molecular polarity and interactions such as hydrogen bonding or dipole-dipole interactions, which impact physical properties like boiling and melting points, solubility, and reactivity.
In the example of B-O bonds, the vast electronegativity difference between boron and oxygen results in strong polarity, which influences how such molecules interact with each other in a chemical environment.

Covalent Bond

Covalent bonding involves the sharing of electron pairs between atoms, leading to the formation of molecules. This bond type highlights the importance of valence electrons as they are shared to achieve full outer electron shells for increased stability.
Covalent bonds can be single, double, or triple depending on the number of shared electron pairs. Oxygen, for example, can form two covalent bonds to fill its valence shell, as illustrated by its typical participation in molecules like water. Analysis of covalent bonding helps understand structure-function relationships in molecules, critical in fields ranging from medicine to materials science.