Atomic Physics Flashcards
What is considered in atomic physics?
Atomic physics are concerned with how the negative electrons are arranged around the positive nucleus, and how the electrons can be excited.
Who is the founder of Atom?
Ernest Rutherford
What is an atom and what does it consist of?
smallest unit of matter which still has the chemical but not necessarily physical properties of an element.
Consists of : Positive nucleus surrounded by cloud of negative electrons, but mostly empty space
What is the radius of the electron cloud and the nucleus?
Radius of electron cloud ≈10-10 m = 0.1 nm (S.I. unit), also = 1Å
Radius of nucleus ≈10-15 m (1 femto-metre, 1fm
(If we expand an atom so the nucleus is 0.5 mm then the edge of the electron cloud is at 50 m!)
What is the nucleus composed of?
The nucleus contains protons and neutrons, held
together by the strong nuclear force
What is a nuclear charge?
The nuclear charge is the total charge of all the protons in the nucleus. It has the same value as the atomic number.
What is the strong nuclear force?
The protons inside the nucleus of an atom all have a positive electrical charge, so they push away from each other. But the strong nuclear force pulls the protons together.
The Strong Nuclear Force is one of the four basic forces in nature (the others being gravity, the electromagnetic force, and the weak nuclear force). As its name implies, it is the strongest of the four.
If a nucleus just had protons, what would happen?
The nucleus would explode, you need neutrons to stabilize
How does the number of protons determine chemical properties?
Even though you change electrons, protons are the same which shows they are responsible - the number of protons doesn’t change, the proton count is basically impossible to change
Neutrons have no charge, and so they don’t affect the number and configuration of electrons. Electrons themselves are too easy to add and remove.
What is 1 Coulomb?
1 Coulomb(macroscopic unit) = is equivalent to the charge of approximately 6.242×1018 electrons. It is the number of electrons transported by a 1A current in 1s time.
What is the charge and mass of the electron?
- 1.602×10-19 C
9. 109×10-31 C
What is the charge and mass of the proton?
- 602×10-19 C;
1. 673×10-27 kg
What is the charge and mass of the neutron?
zero charge;
1.6735×10-27 kg
What is the charge and mass of the positron?
Charge: 1.602×10-19 C
Mass: 9.109×10-31 C
What is a positron?
Antiparticle corresponding to the electron
How do you find A from Coulomb?
Charge x Coulomb = in A
How do two bodies orbit around each other?
If we have an attractive gravitational force between two bodies they can orbit around each other, for example
Earth around the Sun, or satellite around the Earth.
What is the path of the orbit called?
The path of the orbit is called the orbital.
Taking the hydrogen atom into account, why does the electron orbit around the nucleus?
In a hydrogen atom there is an attractive electrostatic force between the negative electron and the positive
nucleus.
Thus, we expect an electron to orbit around the nucleus. This gives us the electron orbitals in the Bohr model of the atom
As an electron gets nearer to the nucleus, what happens to its potential energy?
its PE is lower (more negative).
What is needed to free the electron from an atom?
For an electron in an atomic orbital
energy would have to be added to free
the electron form the atom – we say the
electron is in a bound state.
What is the bound state?
A bound state is a special quantum state of a particle subject to a potential such that the particle has a tendency to remain localised in one or more regions of spac. Once the electron starts to “orbit” the proton, the energy becomes negative, and a bound state – namely the hydrogen atom – is formed.
What kinetic and potential energy does an electron at rest have?
A free electron at rest in empty space will have zero KE and PE
What kinetic and potential energy does an electron in its bound atomic state have?
But in a bound atomic state the sum of KE and PE is less than zero – negative energy.
What is energy quantisation?
Quantum mechanics predicts that the energy levels of bound electrons can only have certain values – energy quantisation.
What is the lowest energy level and what are the other states?
Lowest energy level: ground state
Other levels: excited states
Above the zero energy the electron, what is it?
Above the zero energy the electron is free
– the atom is ionised
What happens when an atom is given energy?
An excited atom can make a transition to a lower energy level and emit a “packet” of light energy called a photon (Photon energy = energy difference between atomic levels.)
What is a photon?
a particle representing a quantum of light
For a photon with energy E the frequency f of the light wave is given by:
E = hf, where h= 6.26×10-34J s is
Planck’s constant.
If f = c/λ, then E = hc/λ.
How does atom absorb light?
An atom can also absorb light of with certain frequencies, or wavelengths and thus we speak of the emission spectrum and absorption spectrum.
What do electrons occupy in an atom?
Definite energy levels orbiting the nucleus
Who discovered the existence of energy levels?
Niels Bohr
How did Niels Bohr find the existence of energy levels
He studied the emission spectra of hydrogen atoms that had been given energy and found a series of lines of specific energy, indicating that only specific energy jumps [absorbance and emissions] were possible in an atom
What provides strong evidence for the existence of energy levels within the atom?
Line spectra
What is the name given to the spectra of Paschen, Balmer, Lyman?
Electromagnetic spectrum
What region of the electromagnetic spectrum does Paschen lie?
Infrared [passion-red]
What region of the electromagnetic spectrum does Balmer lie?
Visible
What region of the electromagnetic spectrum does Lyman lie?
Ultraviolet
What is an energy level?
It’s the fixed amount of energy that an electron can have in an atom
What is an emission spectrum?
a spectrum of the electromagnetic radiation emitted by a source.
What is an absorption spectrum?
a spectrum of electromagnetic radiation transmitted through a substance, showing dark lines or bands due to absorption at specific wavelengths.
What is a continous spectrum?
spectrum of the light emitted by excited atoms of hydrogen that is due to free electrons becoming bound to a hydrogen ion and emitting photons.
In 1913 Niels Bohr proposed a simple model to explain the spectrum of hydrogen (the simplest atom: 1 proton and 1 electron), what was it?
The electron moves in a circular orbit around the proton
The angular momentum is quantised: L=MVR is quantised L = n x h/2pi (angular momentum is the moment of the momentum)
Bohr found that the energy levels En are given by: En = 13.6 eV / n2 (353)
What is an electron volt?
Electron volt (eV) is a unit of energy. 1 eV is the energy gained by an electron when it is accelerated through a potential difference of 1 V. 1 eV = 1.6×10-19 J
How do you calculate the energy differences between levels?
RH = (1/n1(squared) - 1/n2 (squared)
where n1 = lower
n2 -upper level
1/wave length = RH
Give the three properties of light?
Light can behave like a wave
Light can also behave like a particle – the photo Called wave-particle duality
What did de Broglie suggest about particles?
de Broglie suggested that all particles (electrons, protons…) might sometimes behave as waves
wavelength = h/mv
Example: what is the wavelength of a (kinetic energy) 10 eV electron?
De Broglie wavelength, Λ = h/(2mE)^1/2 Where, h is Planck’s constant m is mass of electron E is energy of the electron Given, E= 10 eV = 10X1.6X10^-19 Joules m= 9.1X10^-31 kg ??? λ = h/mv
What is the wavelength of an electron in the nth
orbital?
2PIrn/n
But his is the circumference of the orbital. Thus the Bohr quantisation of angular momentum corresponds to fitting exactly n electron wavelengths around the orbital, to obtain “constructive interference
What are multi-electron atoms and give examples
Multi-electron atoms: only electron states with certain values of energy and angular momentum are allowed. Electrons with more than one atom, such as Helium (He), and Nitrogen (N), are referred to as multi-electron atoms
How do electrons screen nuclear charge?
Electrons screen nuclear charge – add electrons, less and less attraction until its neutral and no attraction
Why is white light used?
White light – all frequencies of light, only certain photons absorbed, emitted
