Atoms and Light Flashcards
What are atoms made up of?
Protons and neutrons and electrons
How are electrons arranged?
In orbitals around nucleus
How are atoms classified?
How many particles of each type are present
What is atomic number?
The number of protons in the nucleus
What is mass number?
The total no. of nucleons
the number of protons and neutrons in nucleus measured in atomic mass unit
How is atomic mass unit defined?
1/12 the mass of carbon
What is 1 atomic mass unit?
1.6605x10-27 kg
What is a chemical element?
A species of atom with the same atomic number
What is the chemical properties of each element determined by?
Arrangment of electrons in orbitals around nucleus
How many electrons can each orbital hold?
2 electrons
What is energy of electrons in each orbital?
Fixed
What is quantum mechanics?
Probability of finding an electron at a specific position around nucleus
What does Heisen Berg’s uncertainity principle state?
We cannot simultaneouly know the position and momentum of a particle such as an electron
How is each orbital observed?
A region of space in which there is a given probability of finding the electron (e.g. a 95% chance)
What is seen in 2s orbital?
Higher chance of electrons further away from the nucleus
How do you fill orbitals?
Order of increasing energy
1S orbital
1 represents the orbital is in energy level closest to the nucleus
What happens when electrons get near the nucleus?
The lower the energy
What is the order of all chemical element based on?
Atomic number
Chemical properties
Arrangement of electrons
What do groups of periodic table have?
Similar physical or chemical characteristics
What do periods of periodic table have?
Trend in atomic radius, ionization energy, electron affinity, electron negativity
How are ions formed?
When atoms gain or lose electrons
net positive or negative charge
What are Group 18 and what do they have?
the noble gases, they have a full valence shell (outer shell) so are unreactive (He: 1s2, Ne 1s2 2s2 2p6 etc…)
What is electromagnetic radiation?
Transverse wave formed from combined oscillations of electric (E) and magnetic (B) fields
What are the properties of electromagnetic radiation?
- Don’t need a medium to travel through
- Move at speed of light
- Wave like properties e.g. interfere, reflect, refract and diffract
What does a vertical wave represent?
Electric field
What does a horizontal wave represent?
Magnetic field
What are 2 examples of Wave-Particle Duality
- Black body radiation
2. Photoelectric effect and compton effect
What is Black body radiation?
“black body”, an object that absorbs all electromagnetic radiation that falls upon it – none passes through and none is reflected. Since no light is reflected or transmitted, the object appears black when it is cold. However, above absolute zero, a black body emits thermal radiation with a spectrum that depends on temperature
What is photoelectric effect?
When a metallic surface is exposed to electromagnetic radiation, above a certain threshold frequency, the light is absorbed and electrons are emitted (see figure, right). In 1902, Philipp Eduard Anton von Lenard observed that the energy of individual emitted electrons increases with the frequency of the light. This was at odds with Maxwell’s wave theory of light, which predicted that the electron energy would be proportional to the intensity of the radiation. In 1905, Einstein resolved this paradox by describing light as composed of discrete quanta (photons), rather than continuous waves.
What is Compton scattering?
In 1923, Compton investigated the scattering of high energy X-rays and &-ray from electrons in a carbon target. By measuring the spectrum of radiation at different angles relative to the incident beam, he found two scattering peaks. The first peak occurred at a wavelength which matched that of the incident beam, while the second varied with angle. Within the framework of a purely classical theory of the scattering of electromagnetic radiation from a charged particle – Thomson scattering – the wavelength of a low-intensity beam should remain unchanged. Compton’s observation demonstrated that light cannot be explained purely as a classical wave phenomenon. Light must behave as if it consists of particles in order to explain the low-intensity Compton scattering. If one assumes that the radiation is comprised of photons that have a well defined momentum the shift in wavelength can be understood
What are discrete particles of EM radiation called?
Photons
What does EM radiation behave as?
Particles with discrete amount of energy and . momentum
What are energy (E) and momentum (P) of photons related to?
Frequency and wavelength of EM radiation via planck’s constant
What can we think of EM radiation as?
Either waves or particles
What are typically very small?
Energy of atoms and sub-atomic particles
How is energy of particles expressed as?
electron Volt (eV)
What is electron Volt?
The amount of energy gained by an electron as it is accelerated through a potential difference of 1V
What is energy of a photon related to?
Frequency
What is frequency related to?
Wavelength
What is energy related to?
Wavelength
What is energy difference?
delta E = E2-E1 between electrons in 2 orbitals
When do electrons lose energy?
If the electron drops from higher energy state in orbital 2 to lower energy state in orbital 1
Energy is emitted as a photon of EM radiation
What is frequency of photons related to?
Energy difference of orbitals
When do Photon Absorption occur?
If an incoming photon has an energy equal to the difference in energy between the two orbitals then it will be absorbed and the electron will be excited from orbital 1 to orbital 2
How are characteristic X-rays emitted?
elements such as molybdenum when electrons move between energy levels
Why does the characteristic x-ray emission in the spectrum occur because?
High energy electrons from the cathode strike the molybdenum target
They knock out electrons from the lower energy levels leaving a vacancy
Electrons in the higher energy orbitals fall down to fill the gap and emit photons of EM radiation in the x-ray range
