Consider doubly ionized Lithium (Li**), which has 1 electron orbiting a charge +

Question

Consider doubly ionized Lithium (Li**), which has 1 electron orbiting a charge +3 nucleus. Compare a0Li, the most likely distance for the electron in a Li** atom to be from the nucleus, with a0H, the most likely distance for the electron in a hydrogen atom to be from the nucleus, assuming the electron is in the ground state in both cases. Which of the following is true? a0Li a0H What is the maximum wavelength, lambdamax, of light that would completely ionize the Li** (i.e., free the electron from the nucleus)? lambdamax = 0.665 nm lambdamax = 10.1 nm lambdamax = 21 nm lambdamax = 137 nm lambdamax = 487 nm Which of the following statements is true? An ideal metal conducts because each electron 'belongs' to every nucleus in the crystal lattice, while in an ideal insulator, each electron is localized to a single nucleus. Metals conduct much better than insulators because, per gram of material, metals have orders of magnitude more electrons. At sufficiently low temperatures, (intrinsic) semi-conductors arc effectively insulators.

Explanation / Answer

(a)

Force of attraction in Li++=3kQ/r

Force of atraction in H=Kq/r

radius=a=h2/mkQ2

all is constant except Q;

For Li ;Q=3e

For H; Q=e

(a) ao,Li  <  ao,H

(b)

Energy needed to ionize Li++=1.968 *10^-17 J

E=hc/

=hc/E

(b) max = 10.1 nm

(c)

(c) At sufficiently low temperatures, (intrinsic) semi-conductors are effectively insulators.

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