Question

The development of the periodic table and the elucidation of the trends and properties of its elements spanned many decades. Now we can use it to predict the properties and reactivity of elements based only on their location in the periodic table. Let's practice some applications of this.

A) Describe the size difference between chlorine and fluorine. Explain why they are different.

B) If an atom has a high ionization energy(IE), like chlorine, what does that mean electronically, i.e., why does it have a high ionization energy?

C) Write an equation representing the electron affinity a chlorine atom and give the actual number. Why does chlorine have a higher EA than fluorine even though they are in the same group?

D) When atoms gain or lose electrons, their radius changes. Explain why the Ca²⁺ ion is smaller than the Cl^-ion? Are these ions isoelectronc? Explain.

Answer 1

A) Describe the size difference between chlorine and fluorine. Explain why they are different.

Answer

The size difference between Fluorine and Chlorine is due to the atomic number. The atomic number of Fluorine is 9 and contain 9 proton and neutron in its nucleus whereas the atomic number of Chlorine is 17 and it contains 17 protons and neutrons in its nucleus which require more space to accommodate.

The different properties of Fluorine and Chlorine are mainly due to the electronegativity and size. This leads to a very high charge/mass ratio. Fluorine is the most electronegative halogen while Chlorine is the next in the line.

B) If an atom has a high ionization energy (IE), like chlorine, what does that mean electronically, i.e., why does it have a high ionization energy?

Answer

Ionization energy is the amount of energy required to remove a valence electron from the atom or ion in the gaseous state.

Atom + energy      Atom⁺ + e^-

A higher ionization energy means a stable electronic configuration or a strong attraction of the valence electrons from the nucleus (Shorter distance between the nucleus and the outermost electrons). Because of this, it becomes increasingly difficult to remove the electrons

C) Write an equation representing the electron affinity a chlorine atom and give the actual number. Why does chlorine have a higher EA than fluorine even though they are in the same group?

Answer

Cl + e-       Cl-       EA = -349 kJ/ mol

Chlorine has a higher electron affinity than Fluorine because fluorine is a small atom. In Fluorine, the incoming electron is going to a region of space already crowded with electrons and creates an electron-electron repulsion. This repulsion weakens the attraction of the incoming electron and nucleus and lessens the electron affinity

D) When atoms gain or lose electrons, their radius changes. Explain why the Ca²⁺ ion is smaller than the Cl^-ion? Are these ions isoelectronic? Explain.

Answer

When electrons are removed from the atom, the size of the resulting ion decreases. This is because of the fact that the resulting nuclear charge over each electron in the resulting cation will be slightly larger. The opposite is true for anions. As electrons are added, the resulting nuclear charge felt by the outer electrons decrease because the other electrons shield the outer electron from the nucleus.

Ca²⁺ has 20 protons in the nucleus and attract the 8 outer shell electrons with greater force of attraction Whereas Cl^- has 17 protons in the nucleus and attract 8 outer shell electrons with a lesser force of attraction

Both Ca²⁺ and Cl^- are isoelectronic. The electronic configuration can be shown as,

[Ca²⁺] 1s2 2s2 2p6 3s2 3p6

[Cl-] 1s2 2s2 2p6 3s2 3p6