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A hydrogenic atom consists of a single electron orbiting a nucleus with Z protons. (Z=1 would be hydrogen itself,Z=2is ionized helium ,Z=3is doubly ionized lithium, and so on.) Determine the Bohr energies En(Z), the binding energyE1(Z), the Bohr radiusa(Z), and the Rydberg constant R(Z)for a hydrogenic atom. (Express your answers as appropriate multiples of the hydrogen values.) Where in the electromagnetic spectrum would the Lyman series fall, for Z=2and Z=3? Hint: There’s nothing much to calculate here— in the potential (Equation 4.52) Ze2, so all you have to do is make the same substitution in all the final results.

V(r)=-e24πo0˙1r (4.52).

Short Answer

Expert verified

The electronic spectrum would be the Lyman seires fall, forz=2 andz=3 is at,z=2 is3.04×10-8m.

At z=3is1.35×10-8m.

Step by step solution

01

Given

The potential is given by:

V(r)=-e24πo0˙1r

02

Electronic spectrum

Consider a hydrogen, if irradiated with light it will be excited to another energy level. The energies of these photons are easily calculated from the Bohr energy formula:

En=-1n2me42h2(4ΤΤ∈0)2

Lyman lines range fromni=2toni=∞(withnf=1);

the wavelengths range from

03

Finding the electronic spectrum

1λ2=R1-14=34Rλ2=43R

Down to

role="math" localid="1658210586427" 1λ1=R1-1∞=R⇒R1=1R

ForZ=2

λ1=14R=14(1.097×107)=2.28×10-8m

to

λ2=13R=3.04×10-8m,

Ultraviolet.

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Most popular questions from this chapter

What is the most probable value of r, in the ground state of hydrogen? (The answer is not zero!) Hint: First you must figure out the probability that the electron would be found between r and r + dr.

a) Check that the spin matrices (Equations 4.145 and 4.147) obey the fundamental commutation relations for angular momentum, Equation 4.134.

Sz=h2(100-1)(4.145).Sx=h2(0110),sy=h2(0-ii0)(4.147).[Sx,Sy]=ihSz,[Sy,Sz]=ihSx,[Sz,Sx]=ihSy(4.134).(b)ShowthatthePaulispinmatrices(Equation4.148)satisfytheproductruleσx≡(0110),σy≡(0-ii0),σz≡(100-1)(4.148).σjσk=δjk+i∑o'IjklσI,(4.153).

Wheretheindicesstandforx,y,orz,ando'jklistheLevi-Civitasymbol:+1ifjkl=123,231,or2=312;-1ifjkl=132,213,or321;otherwise.

Consider the observablesA=x2andB=Lz .

(a) Construct the uncertainty principle forσAσB

(b) EvaluateσB in the hydrogen stateψn/m .

(c) What can you conclude about<xy>in this state?

(a) Work out the Clebsch-Gordan coefficients for the case s1=1/2,s2=anything. Hint: You're looking for the coefficients A and Bin

|sm⟩=A|1212⟩|s2(m-12)⟩+B|12(-12)⟩|s2(m+12)⟩

such that|sm⟩ is an eigenstate of . Use the method of Equations 4.179 through 4.182. If you can't figure out whatSx(2) (for instance) does to|s2m2⟩ , refer back to Equation 4.136 and the line before Equation 4.147. Answer:

;role="math" localid="1658209512756" A=s2+12±m2s2+1;B=±s2+12±m2s2+1

where, the signs are determined bys=s2±1/2 .

(b) Check this general result against three or four entries in Table 4.8.

(a) Use the recursion formula (Equation 4.76) to confirm that whenI=n-1 the radial wave function takes the form

Rn(n-1)=Nnrn-1e-r/na and determine the normalization constant by direct integration.

(b) Calculate 200a and <r2> for states of the form ψn(n-1)m·

(c) Show that the "uncertainty" in r(δr) is<r>/2n+1for such states. Note that the fractional spread in decreases, with increasing (in this sense the system "begins to look classical," with identifiable circular "orbits," for large ). Sketch the radial wave functions for several values of, to illustrate this point.

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