chapter 2

Question 1

black body radiation

Answer 1

Any radiation leaking out of
the hole has been absorbed and re-emitted
inside so many times that it has come to thermal equilibrium

Question 2

energy distribution in a black body at several temp

Answer 2

energy density increases in the region of shorter wavelengths as the
temperature is raised, and the peak shifts to shorter wavelengths.

Question 3

remark about rayleigh frequency distribution formula

Answer 3

The energy radiated would increase continuously as the frequency ν
increases

Question 4

In the photoelectric effect

Answer 4

electromagnetic radiation incident on a metal

surface causes the metal to emit electrons after acquiring enough energy to escape

Question 5

Observation about photoelectric effect and photons

Answer 5

(1) no electrons are ejected, regardless of the intensity of the radiation, unless its frequency exceeds a threshold value characteristic of the metal.

(2) increasing the intensity of the light increases the number of electrons
emitted but does not affect the kinetic energy of the emitted electrons.

(3) increasing the frequency of the radiation increases the kinetic energy of
the emitted electrons.

Question 6

The photoelectric effect can be understood

Answer 6

if an electron is ejected in a
collision with a particle-like projectile (later named photons), provided the
projectile carries enough energy (Ephoton = hν) to expel the electron from
the metal.

Question 7

The emission of light at discrete frequencies can be understood if we suppose that:

Answer 7

–the energy of the atoms or molecules is confined to discrete values, as
then energy can be discarded or absorbed only in packets as the atom
or molecule jumps between its allowed states.

–the frequency of the radiation is related to the energy difference between
the initial and final states: ∆E = hν.

Question 8

The Schrödinger Equation

Answer 8

The mathematical representation of the wave, that in quantum mechanics
replaces the classical concept of trajectory, is called a wave-function, ψ, and is a function of the coordinates of the particle and also a function of time.

Question 9

Quantum Numbers

Answer 9

Principal quantum number: n = 1, 2, 3, . . .

Angular-momentum quantum number: l = 0, 1, 2, . . . , n − 1

Magnetic quantum number: m = −l, −l + 1, . . . , 0, . . . , l − 1

Question 10

Pauli Exclusion Principle

Answer 10

to determine the manner in which these states are filled: electrons configuration

Question 11

The Spin of an Electron

Answer 11

is an intrinsic angular momentum that every

electron possesses and that cannot be changed or eliminated

Question 12

The Aufbau Principle

Answer 12

electron configurations is based on the the fact that the total energy of the atom should be minimum.

Question 13

Group 0:

Answer 13

inert gases, filled electron shells and stable electron configuration.

Question 14

Groups VIIA & VIA:

Answer 14

elements with one (halogens) or two deficient

electrons from stable structure.

Question 15

Groups IA & IIA:

Answer 15

alkali and alkaline earth metals having, respectively,

one and two excess electrons vs. stable configuration.

Question 16

Group IIIB to IIB:

Answer 16

transition metals with partially filled d-electron

states and in some case one or two electrons in the next higher energy shell.

Question 17

Groups IIIA to VA:

Answer 17

elements with characteristics intermediate between

metals and nonmetals because of their valence electron structure.

Question 18

metallicity can be defined

Answer 18

as the tendency of an atom

to donate electrons to metallic or ionic bonds.

Question 19

Metallicity increases

from

Answer 19

top to bottom and from right to left on the periodic

Question 20

Ionic bonding:

Answer 20

nondirectional bonding between metallic (easily give up their valence electrons) and nonmetallic elements (the horizontal extremities of the table of the elements), such as NaCl, MgO
(usually when the electronegativity difference > 2).

Question 21

Covalent bonding:

Answer 21

stable electron configuration as a result of sharing of
electrons between adjacent atoms (directional bond), such as in nonmetallic elemental molecules (H2, Cl2), heterogeneous molecules (CH4, H2O) and elemental solids (Si, SiC,C). Usually when the electronegativity difference< 0.4)

Question 22

Metallic bonding:

Answer 22

nondirectional, found in metals and their alloys; maximum 3 valence electrons not bound to any particular atom in the solid matrix and are free to drift throughout the entire metal generating an electron cloud and ion cores

Question 23

Secondary Interatomic Bonds

Answer 23

–induced dipoles (due to the distortion of electric symmetry because of
vibrational motion of atoms that would induce the same with adjacent atoms),

i–nduced dipoles and polar molecules (permanent dipoles because of electric dissymmetry such as H2O), and

–polar molecules