Arrange Na, Be, C and Br in Increasing Order of Electronegativity According to the Pauling Scale

Correct Answer: Option (C) – Na < Be < C < Br

Detailed Explanation of the Electronegativity Order

To arrange sodium (Na), beryllium (Be), carbon (C), and bromine (Br) in increasing order of electronegativity, we need to compare their ability to attract a shared pair of electrons toward themselves when they participate in a chemical bond. According to the Pauling scale, the electronegativity values of these elements increase in the order Na < Be < C < Br. Therefore, Option (C) is the correct answer.

The approximate Pauling electronegativity values are:

Na = 0.93

Be = 1.57

C = 2.55

Br = 2.96

Arranging these numerical values from the smallest to the largest gives:

0.93 < 1.57 < 2.55 < 2.96

Therefore:

Na < Be < C < Br

What Is Electronegativity?

Electronegativity is the tendency of an atom in a chemical bond to attract the shared pair of electrons toward itself. When two different atoms form a covalent bond, the bonding electrons are generally not shared equally. The atom with the higher electronegativity attracts the shared electron density more strongly.

For example, if two bonded atoms have significantly different electronegativities, the more electronegative atom develops a partial negative charge, while the less electronegative atom develops a partial positive charge. Therefore, electronegativity is an important concept for understanding bond polarity, molecular polarity, chemical reactivity, and the nature of chemical bonds.

Understanding the Pauling Electronegativity Scale

The Pauling scale is the most widely used scale for comparing the electronegativity of elements. On this scale, fluorine has the highest electronegativity value of approximately 3.98. Elements located toward the lower-left region of the periodic table generally have low electronegativity values, while elements located toward the upper-right region generally have high electronegativity values.

The Pauling scale allows us to compare the relative electron-attracting ability of different atoms. In this question, sodium has the lowest value, followed by beryllium, carbon, and finally bromine. Hence, the increasing order is Na < Be < C < Br.

Periodic Trend of Electronegativity

Electronegativity generally increases from left to right across a period and decreases from top to bottom down a group. This periodic trend helps us compare the electronegativities of elements even when their exact numerical values are not given.

Across a period, the effective nuclear charge generally increases while atomic size decreases. As a result, the nucleus attracts bonding electrons more strongly, causing electronegativity to increase. Down a group, additional electron shells increase the atomic size and shielding effect. The bonding electrons are farther from the nucleus and experience a weaker attraction, causing electronegativity to decrease.

Why Does Sodium Have the Lowest Electronegativity?

Sodium is an alkali metal located in Group 1 and Period 3 of the periodic table. Its Pauling electronegativity value is approximately 0.93, which is the lowest among the four elements given in the question.

Sodium has one valence electron and a relatively large atomic radius. Rather than strongly attracting additional electron density in a chemical bond, sodium has a strong tendency to lose its outermost electron and form the Na⁺ ion. Therefore, sodium has a very low electronegativity and appears first in the increasing order.

Why Is Beryllium More Electronegative Than Sodium?

Beryllium has a Pauling electronegativity value of approximately 1.57. This value is greater than that of sodium but lower than those of carbon and bromine.

Beryllium is smaller in atomic size than sodium and has a stronger attraction between its nucleus and bonding electrons. Its greater effective nuclear attraction allows it to attract shared electrons more strongly than sodium. Therefore, the correct relationship is Na < Be.

Why Is Carbon More Electronegative Than Beryllium?

Carbon and beryllium are both located in Period 2 of the periodic table, but carbon lies to the right of beryllium. Electronegativity generally increases from left to right across a period because effective nuclear charge increases and atomic size decreases.

Carbon has a Pauling electronegativity value of approximately 2.55, whereas beryllium has a value of approximately 1.57. Carbon therefore attracts shared bonding electrons more strongly than beryllium. Hence, Be < C.

Why Does Bromine Have the Highest Electronegativity?

Bromine is a halogen belonging to Group 17 of the periodic table. Halogens have high electronegativity because they require only one additional electron to complete their valence shell. Bromine has a Pauling electronegativity value of approximately 2.96, which is the highest among the four elements listed in the question.

Although bromine is located below carbon in the periodic table, its position far toward the right side of the periodic table and its strong tendency to attract electrons give it a higher electronegativity than carbon. Therefore, C < Br.

Comparison of the Pauling Electronegativity Values

The easiest way to verify the correct increasing order is to compare the approximate Pauling values directly. Sodium has a value of 0.93, beryllium has 1.57, carbon has 2.55, and bromine has 2.96. Since increasing order means arranging from the lowest value to the highest value, the sequence becomes Na, Be, C, Br.

Thus:

Na (0.93) < Be (1.57) < C (2.55) < Br (2.96)

Explanation of All Answer Options

Option (A): Be, Na, C, Br

Option (A) is incorrect because it places beryllium before sodium. Sodium has a lower electronegativity value of approximately 0.93, whereas beryllium has a value of approximately 1.57. Therefore, sodium must appear before beryllium in the increasing order.

Option (B): Br, C, Na, Be

Option (B) is incorrect because it begins with bromine, which has the highest electronegativity among the given elements. In an increasing order, the element with the lowest electronegativity must come first. Bromine should therefore appear at the end of the sequence, not at the beginning.

Option (C): Na, Be, C, Br

Option (C) is correct because the Pauling electronegativity values increase continuously from sodium to bromine. The values are approximately Na = 0.93, Be = 1.57, C = 2.55, and Br = 2.96. Therefore, the correct increasing order is Na < Be < C < Br.

Option (D): Na, C, Be, Br

Option (D) is incorrect because it places carbon before beryllium. Carbon has an electronegativity value of approximately 2.55, which is greater than the value of beryllium, approximately 1.57. Therefore, beryllium must come before carbon in the increasing order.

Factors Affecting Electronegativity

Several factors influence the electronegativity of an atom. A higher effective nuclear charge generally increases electronegativity because the nucleus attracts bonding electrons more strongly. A smaller atomic radius also increases electronegativity because the bonding electrons remain closer to the nucleus. In contrast, a greater shielding effect and larger atomic size generally reduce the attraction for shared electrons.

These factors explain the general periodic trend and help us understand why sodium has the lowest electronegativity in this question, while bromine has the highest. Beryllium and carbon occupy intermediate positions according to their atomic size, effective nuclear charge, and location in the periodic table.

Final Answer

The correct answer is Option (C): Na < Be < C < Br. According to the Pauling scale, the approximate electronegativity values are Na = 0.93, Be = 1.57, C = 2.55, and Br = 2.96. Arranging these values from lowest to highest gives the increasing order Na < Be < C < Br.