Video Transcript
Why is the element nitrogen more electronegative than the element beryllium? (A) Nitrogen has a greater number of electrons in a similar volume, resulting in greater electronegativity. (B) Nitrogen has a greater number of protons and hence an effective nuclear charge that more strongly attracts the bonding electrons. (C) The bonding pair of electrons are closer to the nucleus in beryllium than in nitrogen. (D) Beryllium is a metal, and metals have higher values of electronegativity than nonmetals of the same period. (E) Electronegativity increases as you ascend the groups of the periodic table.
To answer this question, we need to determine why nitrogen is more electronegative than beryllium. Electronegativity is the tendency of an atom to attract the shared electrons of a bond. As nitrogen is more electronegative than beryllium, an atom of nitrogen must more strongly attract the shared electrons of a bond than an atom of beryllium. To understand why, let’s take a look at an atom of nitrogen and an atom of beryllium. An atom of nitrogen has seven protons in its nucleus, two electrons in the first electron shell, and five electrons in the second electron shell. An atom of beryllium has four protons in its nucleus, two electrons in the first electron shell, and two electrons in the second electron shell. We can see that both of these atoms have the same number of electron shells and the same number of innermost electrons.
Let’s consider an outermost electron in each atom. Each of these electrons experiences a similar degree of repulsion from the innermost electrons. The outermost electrons in each atom also experience a force of attraction to the positively charged nucleus. As the positive charge in a nitrogen atom’s nucleus is greater than the positive charge in a beryllium atom’s nucleus, the outermost electrons in a nitrogen atom will be more strongly attracted to the nucleus than the outermost electrons in a beryllium atom. In other words, the net positive charge experienced by an electron or the effective nuclear charge is greater in an atom of nitrogen than an atom of beryllium.
In addition, because the outermost electrons in an atom of nitrogen are more strongly attracted to the nucleus, a nitrogen atom will be smaller than a beryllium atom. The atomic radius and the effective nuclear charge both influence the electronegativity. The electrons in a shared bond with an atom of nitrogen will be both closer to the nucleus and more strongly attracted due to the greater effective nuclear charge than the electrons in a shared bond with an atom of beryllium. So, we now know that nitrogen is more electronegative than beryllium because the nitrogen atom has a greater effective nuclear charge.
From this, we can deduce that answer choice (B) is the correct answer. The element nitrogen is more electronegative than the element beryllium because nitrogen has a greater number of protons and hence an effective nuclear charge that more strongly attracts the bonding electrons, or answer choice (B).
