Question

1.Getting sunburned is dangerous as well as painful. Too much exposure to high energy electromagnetic (EM) radiation can lead to cellular DNA damage causing an increased risk for cancer. You know that DNA damage occurs if the energy of the incident, EM radiation, is above a certain threshold. What would you predict is worse based on your knowledge of quantum theory - a weak beam of ultraviolet light, or an intense beam of infrared light? Explain your reasoning.

2. The atomic emission spectrum for hydrogen contains four different lines (i.e., wavelengths of light) in the visible region of the electromagnetic spectrum. Explain why only four, discrete wavelengths of light are observed instead of a continuous spectrum of wavelengths.

3. Sketch the shapes of the following atomic orbitals. For each sketch, indicate the position of the nucleus, and the spatial orientation of the atomic orbital with respect to a Cartesian coordinate-axis system. a) 1s b) 2px, 2py, and 2pz c) 3dxy, 3dxz, 3dyz, 3dx2-y2, and 3dz2

4. In the early part of the 20th century, Niels Bohr proposed a model for the hydrogen atom that explained the experimentally observed emission spectrum for hydrogen. a) List and describe two of the assumptions that Bohr made in his model for the hydrogen atom. b) List and describe two limitations of the Bohr model.

Answer 1

1) Exposure to weak UV light is dangerous than to intense IR light. Because, UV light has high energy with shorter wavelength, which is very much higher in energy than the threshold limit. Where as I R is a low energy radiation than the visible light. Hence less dangerous

2) As hydrogen is an atom and atoms exhibit discontinuous line spectra due to deexcitation of the excited electron from high energy level to low energy level with some specific energy values and it happens only when energy is supplied. Hence it is discontinuous.

3) S orbital is Spherical in shape

P is dumbbell & d is double dumbbell in shape

4) a) Bohr explained that the energy levels of atoms are quantized with an angular momentum, mvr= nh/2pi

He clearly explained the line spectrum of H atom

b) Bohr failed to explain the spectra of multi electron species

He couldn't explain about Zeeman & Stark effects ( splitting up of spectral lines)

He ignored wave nature of electron & contradicted the Heisenberg' S uncertainty principle