Supplementary Lecture 1 Flashcards
what does quantum mechanics inform us in terms of electrons?
quantum mechanics informs us that small particles such as electrons have wave-like properties
Heisenberg Uncertainty Principle:
means the exact position of an electron cannot be specified; only the probability that it occupies a certain region of space
atomic orbital:
mathematical description of the wave properties of an electron
higher principle quantum number:
higher energy and more nodes
valence shell:
the outermost shell of electrons in an atom is its valence shell
fully occupied valence shells in periods beyond the first contain…
… 8 electrons
octet rule:
the tendency of atoms to form ions with the noble-gas configuration
the number of valence electrons =
the elements group number
what is the energy like in an atomic orbital?
an atomic orbital has a discrete quantized energy
what is each orbital characterised by?
each orbital is characterised by a 3D region of space in which the electron is probably going to be found
what is shape described by?
shape is described by orbital sublevel (s, ,p etc)
multiple orbitals of same type have the same shape and energy but…
… differ in direction
what do larger higher energy atomic orbitals have?
nodes
the higher the energy of an a-orbital…
… the more nodes
how do all valence electrons exist in covalent compounds?
all valence electrons from atoms in covalent compounds surround all of the nuclei and are delocalised
how many bonds can the following atoms make; hydrogen, carbon, nitrogen & oxygen
hydrogen = 1 bonds
carbon = 4 bonds
nitrogen = 3 bonds
oxygen = 2 bonds
formal charge =
valence number - no. of electron lone pairs - no. of bonds
formal charge of nitrogen when possessing the following number of bonds; 2 bonds, 3 bonds & 4 bonds
2 bonds = -1
3 bonds = 0
4 bonds = +1
formal charge of oxygen when possessing the following number of bonds; 1 bonds, 2 bonds & 3 bonds
1 bond = -1
2 bonds = 0
3 bonds = +1
how can you find out the formal charge of an atom in a compound?
count all non-bonding valence electrons and half of the bonding electrons
why might the lewis structure of a compound not be an accurate depiction and how can it be made accurate?
this is as lewes structures do not represent the polarisation of electron density, to fix this one can add partial charges or draw resonance structures
when are resonance structures used?
resonance structures are used when a lewis structure does not accurately represent the bonding and electron delocalisation
bonding orbitals from 1s-1s and 2s-2s interactions are…
…cylindrically symmetrical
what are σ (sigma) bonds and how are they made?
sigma bonds are bonding orbitals with cylindrical symmetry, they can be made by combining s or p orbitals
hybridisation:
a model and not an observable truth. We use it to rationalize structure and chemical behaviour. Molecular orbital theory is the more advanced model.
what happens to the orbitals of atoms once they join a compound?
upon joining a compound the atomic orbitals will hybridise into molecular orbitals
what shape do molecular orbitals have?
these molecular orbitals have shapes that resemble the atomic orbitals
hybridisation:
the concept of mixing atomic orbitals to form new hybrid orbitals
Molecular structure is revealed by knowing a molecule’s:
constitution and molecular geometry
what is each orbital characterised by?
each orbital is characterised by a 3D region of space in which the electron is probably going to be found
how do all electrons behave in the valence shell of covalent compounds?
all valence shell electrons from atoms in covalent compounds surround all of the nuclei and are delocalised
what causes a polar covalent bond?
polar covalent bonds are caused by two atoms with highly differing electronegativity
what does dipole moment (m) depend on?
Dipole Moment (m) depends on charge separation and distance
why are lewis structures bad and how can we fix their problems?
lewis structures are bad because they are a gross simplification, not taking into account molecular shape and partial charges - something that can be fixed with resonance structures (partial charges etc)
what does resonance allow us to improve our understanding of?
resonance will allow us to enhance out understanding of bonding
