/
Atomic Structure Flashcards
Save to my account
Sign up
Atomic Structure Flashcards
Atomic Structure Flashcards
Study
1
Question
What are the important characteristics of cathode rays?
Answer
Cathode rays travel in straight lines, can pass through thin layers, are emitted from the cathode surface, have high kinetic energy, are deflected by electric and magnetic fields, produce fluorescence, produce chemical changes, and produce X-rays when striking a metal target.
2
Question
Who made the first precise measurement of the charge on an electron and when?
Answer
Robert A. Millikan in 1909, using the oil drop experiment.
3
Question
What is the 'rest mass' of an electron, and what is its value?
Answer
It's the mass of the electron when it is moving with low speed. It is calculated to be 9.1096 × 10−28 g or 9.1096 × 10−31 kg.
4
Question
Who discovered protons and how?
Answer
Goldstein (1886) used perforated cathode and noticed the emission of positive rays or canal rays.
5
Question
How does the specific charge of canal rays vary with the nature of the gas used?
Answer
The specific charge (e/m) of canal rays particles varied with nature of gas and was found to be maximum if H2 was used.
6
Question
What are the key features of Thomson's atomic model?
Answer
The atom is considered as a sphere of positive charge with electrons distributed within, mass of atom is spread uniformly, radius of 10−10 m.
7
Question
What were the observations made in Rutherford's alpha-scattering experiment?
Answer
Most α-particles went straight, some were deflected through small angles, and a very small number rebounded.
8
Question
What were the conclusions drawn from Rutherford's alpha-scattering experiment?
Answer
Many particles went straight through indicating large empty space, some were deflected indicating positive charge concentration in nucleus, and very few rebounded indicating a rigid nucleus.
9
Question
What parameters are related in Moseley's relationship?
Answer
Frequency of X-rays, atomic number (Z), and constants a and b. ν = a(Z-b)
10
Question
How was the neutron discovered?
Answer
Chadwick bombarded beryllium with α-particles to produce neutral particles called neutrons.
11
Question
What are the main postulates of Rutherford's nuclear atomic model?
Answer
An atom consists of a positively charged heavy nucleus, the nucleus is very small, there is an empty space around nucleus, and electrons revolve around the nucleus.
12
Question
What are the main drawbacks of Rutherford's atomic model?
Answer
Electrons should lose energy continuously and fall into the nucleus, and the observed spectra should be continuous, not line spectra.
13
Question
Define isotopes, isobars, isotones, and isoelectronic species.
Answer
Isotopes: Same atomic number, different mass numbers. Isobars: Different atomic numbers, same mass number. Isotones: Same number of neutrons. Isoelectronic: Same number of electrons.
14
Question
What are the key characteristics of electromagnetic radiations (EMR)?
Answer
All electromagnetic radiations travel with the velocity of light. They consist of electric and magnetic fields that oscillate in directions perpendicular to each other and perpendicular to the direction in which the wave is travelling.
15
Question
What are the six characteristics of waves?
Answer
Wavelength (λ), Frequency (ν), Velocity (c), Wave number (ν̄), Amplitude (A), Time period (T).
16
Question
What is an electromagnetic spectrum?
Answer
Arrangement of various types of electromagnetic radiations in the order of their increasing or decreasing wavelengths or frequencies.
17
Question
What is the key difference between emission and absorption spectra?
Answer
Emission spectra give bright lines on a dark background. Absorption spectra give dark lines on a bright background.
18
Question
What are the different spectral series of hydrogen and in which region do they appear?
Answer
Lyman series (Ultraviolet), Balmer series (Visible), Paschen, Brackett, Pfund, Humphrey series (Infrared).
19
Question
What is Ritz mathematical formula to find the wavelengths of various hydrogen lines?
Answer
v/c = 1/λ = R (1/n1^2 – 1/n2^2) where R is Rydberg constant, n1 and n2 are integers.
20
Question
What causes the appearance of dark lines on the bright background in absorption spectra?
Answer
When the radiations from a continuous source pass through a sample of hydrogen gas, then the wavelength missing in the emergent light gives dark lines on the bright background.
21
Question
What is Einstein's view on the nature of light?
Answer
Light consists of a stream of particles called photons, and the energy of each photon depends on the frequency of the light: E = hv.
22
Question
What is photoelectric effect, work function, and stopping potential?
Answer
Photoelectric effect is the emission of electrons from a metal surface when exposed to light radiations. Work function is the minimum energy to eject electrons. Stopping potential is the minimum potential at which photoelectric current becomes zero.
23
Question
What is the quantum theory of radiation?
Answer
Max Planck proposed that a hot body emits radiant energy discontinuously in small packets called quanta with energy E = hν.
24
Question
What are the laws of photoelectric effect?
Answer
Rate of emission is proportional to intensity, maximum kinetic energy is proportional to frequency (independent of intensity), no time lag, frequency must be equal or greater than threshold frequency.
25
Question
What is the formula for the energy of a photon?
Answer
Energy of a photon = hν = hc/λ
26
Question
What is the equation relating photon energy (E), minimum energy to remove an electron (E0), and kinetic energy (KE) of photoelectrons?
Answer
E = E0 + KE, where E0 is the minimum energy to remove an electron and KE is the kinetic energy of photoelectrons emitted.
27
Question
Write the photochemical dissociation reaction of oxygen into one normal oxygen atom and one excited oxygen atom.
Answer
O2 -> ONormal + OExcited
28
Question
Describe Bohr's postulate about electron orbits.
Answer
Electrons revolve around the nucleus in circular orbits without losing energy in stationary orbits.
29
Question
What is the formula for the angular momentum of an electron in a Bohr orbit?
Answer
mvr = nh/2π, where n = 1, 2, 3,...
30
Question
What is the formula for the energy change when an electron jumps between orbits?
Answer
∆E = E_high - E_low = hν