CEM 141 Lecture 20: CEM 141 10/17 Lecture 20 (Periodic Table Trends continued)

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24 Oct 2018

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Ions: atoms in which electrons have been added or removed. If an electron is removed from an atom, the ion will be positively charged. Cation: when an electron is removed from an element. Li has a larger radius than li+ Becauseli has one more electron than li+ Li+ has less electrons and those electrons will be held closer to the nucleus than in li. Anion: when an electron is added to an element. F- has a larger radius than f. Becausef- has one more electron than f. F- has more electrons meaning there are more repulsions between the electrons and protons (in the nucleus), meaning it will be larger. Although both atoms have the same electron configurations, they have different sizes due to their attractive forces between different (due to the different number of protons) Na+ has more protons attracting its electrons, so it their electrons will have a stronger pull toward the nucleus, making it smaller than f-

Related Questions

True or False.

(a) Effective nuclear charge (Zeff) is the positive charge experienced by the electron from the nucleus and it increases from left to right across the period. Answer: __________

(b) Effective nuclear charge slightly decreases going down a group. Answer: __________

(d) Atomic radius tends to decrease from top to bottom of a group because of the increase in the principle quantum number. Answer: __________

(e) Anions are larger than their parent atoms because electrons are added to the valence shell reducing the electron-electron repulsions. Answer: __________

(f) Al3+ is larger than Na+ because Na+ has two extra electrons. Answer: __________

(g) The ionization energy of Na2+ is significantly higher than Na+ because it takes more energy to remove the inner-shell electron. Answer: __________

(h) Bromine, calcium and sodium are metallic elements because they are on the left side of the periodic table. Answer: __________

(i) Calcium, antimony, and silicon are metalloids that their properties fall between those of metals and those of nonmetals. Answer: __________

(j) Lattice energy is the energy required to completely separate one mole of solid ionic compound into its gaseous ions and it is always a negative number. Answer: __________

Ionic Radii

The size of ions as measured by ionic radii varies in a systematic manner. The size of the ion can be explained in part by effective nuclear charge, Zeff, which is the net nuclear charge felt by an electron. The effective nuclear charge takes into account the actual nuclear charge and the shielding of this charge by inner electrons. When an atom loses electrons, the resulting cation is smaller both because the remaining electrons experience a larger Zeff and because these electrons are usually in orbitals closer to the nucleus than the electrons that were lost. The more electrons that are lost, the smaller the ion becomes.

Similarly, when an atom gains electrons, the resulting anion is larger owing to both increased electron-electron repulsions and a reduction in Zeff. The more electrons that are gained, the larger the ion becomes.

Part A

Rank the following ions in order of decreasing radius: O2â,S2â,Se2â,Te2â, and Po2â. Use the periodic table as necessary.

Rank from largest to smallest radius. To rank items as equivalent, overlap them.

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Part B

Rank the following items in order of decreasing radius: Na, Na+, and Naâ.

Rank from largest to smallest radius. To rank items as equivalent, overlap them.

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Part C

The following ions contain the same number of electrons. Rank them in order of decreasing ionic radii.

Rank from largest to smallest radius. To rank items as equivalent, overlap them.

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CEM 141 Lecture 20: CEM 141 10/17 Lecture 20 (Periodic Table Trends continued)

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