Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
MESA COMMUNITY COLLEGE PHYSICAL SCIENCE DEPARTMENT CHM151: GENERAL CHEMISTRY I – DR. NACHMAN Electron Shielding (adapted from J.E. Huheey, Inorganic Chemistry , 3 rd ed, Harper & Row, New York, 1983) The calculated energy of a one-electron atomic orbital varies as Z 2 /n 2 . Since the nuclear charge (or atomic number) increases more rapidly than the principal quantum number, one might expect that the energy necessary to remove an electron from an atom (the ionization energy, IE) would continually increase with increasing atomic number. By comparing hydrogen ( Z = 1, IE = 1312 kJ mol –1 ) with lithium ( Z = 3, IE 1 = 520 kJ mol –1 ), you can see this doesn’t actually happen. Lithium has a lower ionization energy for two reasons: (1) a 2 s electron has a greater average distance from the nucleus than a 1 s electron (see Fig. 7.23, p. 284 in Ebbing); (2) the inner core 1 s 2 electrons in lithium repel the outer 2 s 1 electron, so the outer electron comes away more easily than it would in the absence of the core electrons. Rather than think of the core as repelling the outer electrons, we may model the core electrons as “shielding” or “screening” the nucleus, as if the outer electron feels the attraction of only part of the total charge at the nucleus. From the viewpoint of the outer electron, the lithium atom’s
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

Page1 / 2


This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online