Chemical bonding lecture 4 Flashcards
What is electron spin?
it is a quantum number based on the fact that electrons have not only position but also spin where the spin is considered a form of angular momentum.
electron spin can only take two values:
The up spin ms= 0.5
the down spin ms = -0.5
what are the two rules/restrictions that must be followed when adding electrons?
- Pauli exclusion principle: no two electrons in an atom can have the same set of quantum numbers (in each orbital the two electrons must have different magnetic spin).
- when electrons are added to orbitals of the same energy, a single electron fills each orbital individually then a second electron enters the same orbital. In addition, the lowest energy configuration is one with parrel spins.
what are paramagnetic and diamagnetic substances?
paramagnetic - it is a substance that is attracted to the magnetic field due to it having one or more unpaired electrons in its structure( it is attracted since a magnetic moment arises from each of the unpaired electrons).
Diamagnetic - it is a substance that is used out of the magnetic field due to all its electrons being paired.
note: The force experienced by paramagnetic substances is greater than the force experienced by diamagnetic substances.
what is photoelectron spectroscopy?
it is a method used to determine the energy of an orbital by measuring the ionization energy required to remove an electron from a free atom.
This is done as follows:
A sufficient amount of radiation with frequency v strikes an atom causing an electron to be ejected with a certain kinetic energy, the said kinetic energy can then be determined by passing an electron through an energy analyzer, which records the amount of voltage required to deflect the electrons around a semicircular pathway in a vacuum to reach the detector. The voltage can be changed for different detections. The equation E = hv - kinetic energy can then be used to find the energy of the atomic orbital.
what is the Koopmans’ and frozen orbital approximation?
Koopman’s approximation -
What happens to the atomic radii when we go down a group and across a period
- Down the group results in an increase in radius due to Pualing’s rule where electrons need to be placed in further away orbitals
- across the group results in a smaller radius as according to Coulomb’s law of attraction, more protons in the nucleus pull the electron in the valence shell closer to them
What is the observation seen as we go down the group of ions with noble gas configuration?
The increase of the ionic radius is significant until we reach the D block period at which the radius increase starts to become less significant due to the decreases of radius across the D block period.
Note similar happens when we reach the F period explained by a phenomenon called Lathide contraction
if still confused page 264
how can we use the molar volume to measure the atomic radii?
by considering the size of an atom and the geometry of the bonds that connect them, we can use the molar volume of a solid to determine the relative size of an atom, where it is seen that alkali metals have the largest molar volume due to the fact they have large atoms and that they are organized in a open closely packed structure.
What are teh two reasons that ionization energy decreases down the group (1)? Why does oxygen have a smaller ionization energy than nitrogen (2)? Why is boron IE less than beryllium (3)? What is the trend in 2IE
- because the quatum number increases so we move to a further orbital so less nuclear pull, and since we have more electrons in lower energy levels there is more screening.
- since the electron added in the P orbital for oxygen is being added to a subshell with another electron the repulsion causes for an easier removal of electrons.
- the electron is added to a less stable 2p orbital in boron
- the same as IE1 but shifted by one to the left (Ya3ni all the trends are the same base we start from He and work our way so instead of the observation seen by Boron and Be we shift one element to the right and it’ll be boron and carbon)
What is the zero-point energy?
It is the lowest possible energy a molecule can have and the bond dissociation energy is based on it.
what happens when two atoms approach each other? (in terms of wave properties)
When two atoms are near each other their electron density interpenetrate each other, resulting in a new electron density. Due to wave electron property of electrons the two atomic electronic wave functions then interact and either constructively or destructively interact, if they interact constructively the increase of electron density causes a stable structure to form between the two atoms
How do we use the Born-Oppenheimer approximation?
- Take the nucleus to be in a fixed position, then solve Schodinger’s equation for electrons moving around this fixed position then get corresponding quantized energy levels and quantized wave function. Repeat the same calculations but at a different fixed position.
- We take the lowest quantized energy that we found and take it as the effective potential energy as a function of the relative distance (this gives us the bond length and dissociation energy). We then use the effective potential energy we have and the kinetic energy to construct and solve a Schodinger’s solution which will then give us the corresponding energies for vibrational motion and rotational motion.
What are the main points of the H2^+ model?
- the potential energy is the attractive forces between the electron and the protons - the repulsive forces between the protons
- we use ellipsoidal coordinates of (Ra,Rb, angle) where Ra and Rb are the distance from the protons to the electron respectively, and the angle gives the same potential energy no matter its value
- we use the Born-Oppenheimer approximation for a set value of Rab ( the distance between the protons) and we find the electronic wave function 𝚿el(Ra, Rb, angle; Rab) with the semi column indicating a fixed parameter for the nuclear coordinates and since the angle always gives the same potential energy we emit it from the calculation.
What are the Molecular orbitals introduced? (Explain what they mean)
Notes
What is the LCAO approximation and Correlation diagram?
Notessss
