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Examples: Cl 99 ppm and Cl- 181 pm; O 73 pm and O2- 140 pm

2006-10-16 11:39:58 · 3 answers · asked by bebeeangeldust 4 in Science & Mathematics Chemistry

3 answers

Anions have negative charge. This means they gain electron. After atoms gain electron, the effective nuclear charges felt by the valence electrons (outer most electrons) decreases. For example, neutral Cl chlorine has 17 protons and 17 electrons. Before it gains an electron, the effective nuclear charges felt by the 7 valence electrons is also 7. However, after Cl gains one election it will have 18 electrons. 8 valence electrons will still feel a effective nuclear charge of 7, since proton does not increase. Since that added electron will compete with other 7 electrons, on average, each valence electron feel less attraction from the nucleus. Thus elections are farther away from the nucleus. Therefore, the radius of an anion always larger than the atom from which it is derived.

2006-10-16 12:10:32 · answer #1 · answered by pyx 2 · 0 0

An anion adds electrons when it forms an ion. The extra electron adds to the repulsion of the other electrons around the nucleus. The extra repulsion causes the radius of the ion to increase when compared to the radius of the atom.

2006-10-16 18:42:57 · answer #2 · answered by physandchemteach 7 · 0 0

because anions are the ones that gain electrons...cations are smaller...they lose electrons

2006-10-16 18:44:37 · answer #3 · answered by norm n 2 · 0 0

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