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13. when a chlorine atom forms an ion its radius increases, but when a …

Question

  1. when a chlorine atom forms an ion its radius increases, but when a sodium atom forms an ion its radius decreases. explain this apparent contradiction.
  2. choose which has the:

a) lowest first ionization energy: k, na, ca
b) largest radius: s²⁻, cl⁻, cl
c) highest electronegativity: as, sn, s
d) smallest atom: na, li, be
e) highest first ionization energy: c, n, si

  1. lithium, cesium, potassium, sodium, rubidium

a) place the elements above in order from smallest atomic radius to largest atomic radius.
b) place the elements above in order from smallest ionization energy to largest ionization energy.
c) place the elements above in order from smallest electronegativity to largest electronegativity.

  1. in each of the following pairs, circle the species with the higher ionization energy:

a) li or cs
b) cl or ar
c) ca or br
d) na⁺ or ne
e) b or be

  1. determine which element you would expect to have the lowest first ionization energy: li, cs, h, he, ba
  2. identify which atom should have the largest value for the electron affinity: he, f, na, si, mn
  3. define ionization energy.
  4. is it easier to form a positive ion with an element that has high ionization energy or an element that has low ionization energy? explain.
  5. what trend in ionization energy do you see as you go down a group/family on the periodic table? what causes this trend?
  6. circle the atom in each pair that has the greater electronegativity:

a) ca ga
b) li o
c) cl s
d) br as
e) ba sr
f) o s

  1. ca sr ba mg

a) most metallic?
b) least metallic?
c) lowest electronegativity?
d) highest ionization energy?
e) largest atomic radius?
f) which are non - metals?
g) list them in order from small to large.
h) would they gain or lose electrons to form ions? what charge would the ion have?
i) would the ion be larger or smaller than the atom?
k) would the ions be cations or anions?
l) what is the special name given to the group in which these elements belong?

Explanation:

Question 13 (Explanation - Step by Step)

Step 1: Analyze Chlorine Atom to Ion

A chlorine atom (\(Cl\)) has 7 valence electrons. When it forms an ion (\(Cl^-\)), it gains 1 electron. This addition of an electron increases electron - electron repulsions in the valence shell. Also, the effective nuclear charge experienced by the outermost electrons remains relatively the same (since the nuclear charge doesn't change, but the number of electrons increases). The increased repulsions cause the electron cloud to expand, so the radius of \(Cl^-\) is larger than that of \(Cl\).

Step 2: Analyze Sodium Atom to Ion

A sodium atom (\(Na\)) has 1 valence electron. When it forms an ion (\(Na^+\)), it loses this valence electron. Now, the ion has one less energy level (the outermost shell is removed). Also, the effective nuclear charge experienced by the remaining electrons increases (since there are fewer electrons to shield the nuclear charge). This causes the remaining electrons to be pulled closer to the nucleus, so the radius of \(Na^+\) is smaller than that of \(Na\).

Step 1: Recall Ionization Energy Trends

Ionization energy generally decreases as we move down a group and increases as we move across a period from left to right.

Step 2: Analyze the Elements

\(K\) (potassium) and \(Na\) (sodium) are in Group 1, with \(K\) below \(Na\). \(Ca\) (calcium) is in Group 2. Down a group, ionization energy decreases, so \(K\) has lower ionization energy than \(Na\). Also, Group 1 elements have lower ionization energy than Group 2 elements in the same period. So among \(K\), \(Na\), \(Ca\), \(K\) has the lowest first ionization energy.

Step 1: Recall Radius Trends for Atoms and Ions

For anions, the more negative the charge (or the larger the number of electrons relative to protons), the larger the radius. Also, anions are larger than their parent atoms.

Step 2: Analyze the Species

\(S^{2 - }\) has 18 electrons, \(Cl^-\) has 18 electrons, and \(Cl\) has 17 electrons. The nuclear charge of \(S\) is \( + 16\) and for \(Cl\) is \( + 17\). Since \(S^{2 - }\) has a smaller nuclear charge than \(Cl^-\) but the same number of electrons, the electron cloud in \(S^{2 - }\) is less tightly held. Also, \(Cl^-\) is larger than \(Cl\) (anion vs atom). So \(S^{2 - }\) has the largest radius.

Answer:

Chlorine gains an electron (increasing electron - electron repulsions and keeping effective nuclear charge similar, expanding the electron cloud). Sodium loses a valence electron (losing a shell and increasing effective nuclear charge, pulling electrons closer), leading to the apparent contradiction.

Question 14a (Explanation - Step by Step)