Samenvatting Scheikunde 1 voor BFW
Hoofdstuk 6 Quantum Theory and the Electronic Structure of Atoms
6.1 Wavelength
Frequency (v)
Speed of light 2,9979458 x 108 m/s
An electromagnetic wave has an electric field component and a magnetic field
component, same wavelength, frequency and amplitude, but they vibrate in two
mutually perpendicular planes. Waves can make an interference pattern.
6.2 Blackbody radiation
Radiant energy could only be emitted or absorbed in discrete quantities,
quantum is the smallest quantity of energy.
h is Planck constant, 6,63 x 10-34 J/s.
By the photoelectric effect are electrons ejected from the surface of a metal
exposed to light of at the least a certain minimum frequency, called the threshold
frequency. Photons are sent to the metal, so a beam of light is really a stream of
particles. A photon has kinetic energy while moving.
KE is kinetic energy and W in binding energy, both in eV (1 eV = 1,602 x 10-19 J)
The more energetic the photon, the greater the kinetic energy. Overall, the more
intense the light, the greater the number of electrons emitted by the target metal;
the higher the frequency of the light, the greater the kinetic energy of the ejected
electrons.
6.3 Atomic line spectra
Emission spectra
Continuous spectra are spectra wherein all wavelengths of visible light are
presented.
Specific wavelengths
R is Rydberg constant 1,09737316 x 107 m-1.
An electron is allowed to occupy only certain orbits of specific energies, thus
energies of the electron are quantized.
Energy of electron is given by
The ground state is the lowest energy state of an atom. Electrons can come from
the ground state into the excited state.
A photon is emitted from the atom when ni > nf.
, 6.4 De Broglie: If energy (light) can, under certain circumstances, behave like
a stream of particles (photons), then perhaps particles such as electrons can,
under certain circumstances, exhibit wavelike properties.
Only certain wavelengths of an electron are allowed.
Particle and wave properties are related by
6.5 Heisenberg uncertainty principle: It is impossible to know simultaneously
both the momentum p and position x of a particle with certainty.
For a particle with mass m
6.6 There are three quantum numbers to describe the distribution of electron
density.
Principal quantum number (n) for the size of the orbital. N = 1, 2, 3…
Angular momentum quantum number (l) for the shape of the orbital. L =
0 to n-1. 0=s, 1=p, 2=d, 3=f
Magnetic quantum number (ml) describes the orientation of the orbital in
space. In subshell, the value of ml depends of value of l. Ml = (2l+1)
A collection of orbitals with the same value of n is frequently called a shell. One
or more orbitals with the same n and l values are referred to as a subshell.
Electrons are like tiny magnets. The electron spin quantum number ms give the
direction of the spin, -½ or ½.
6.7 For any value of the principal quantum number n, 0 is possible for l. A
value of l=0 corresponds with an s subshell. There is an s subshell in every shell,
and each s subshell contains one orbital.
With an n value of 2 or more, 1 is possible for l, corresponding to a p subshell.
The values of ml, -1,0,1, are corresponding with three p orbitals.
6.8 Ground-state electron orbitals
The energy of an orbital in a many-electron system depends on both the value of
n and the value of l. In a many-electron atom, for a given value of n, the energy of
an orbital increases with increasing value of l. So, a 4s orbital is lower in energy
than the 3d orbitals.
According to the Pauli exclusion principle, no two electrons in the same atom can
have the same four quantum numbers. One must have ms = +½ and one must
have ms = -½. So, a maximum of two electrons may occupy in an atomic orbital,
and those two electrons must have opposite spin. An orbital with a single
electron is represented with an upward arrow.
Aufbau principle: each step involves adding one proton to the nucleus and one
electron to the appropriate atomic orbital. With the Hund’s rule, the number of
electrons with the same spin is maximized. Accordingly, in any subshell, an
