Section A Flashcards
What is the most abundant element in the human body?
Oxygen at ~65%, present in water, lipids, carbohydrates
What is the second most abundant element in the human body?
Carbon at ~18% of your mass, key in proteins, sugars, lipids
What is the spin of an electron/proton/neutron?
All are 1/2 spin
What varies in an isotope, and what can we use to measure this?
Neutron number varies, mass spectrometer used to measure
What is the mass in Kg of one atomic mass unit (AU)?
1.6605 x 10-27Kg
What is the definition of a mole?
A substance containing Avogadro’s number of molecules, 6.022 x 1023
What is Avogadro’s number (NA)?
6.022 x 1023
What is the Aufbau principle?
Principle of ‘building up’ of electron shells, electrons occupy lower energy orbitals first
What is the Pauli exclusion principle?
No 2 electrons can have the same 4 quantum numbers
What is a wave function?
Mathematical description of distribution of an electron in terms of position and time
What is the uncertainty principle?
Position and momentum cannot simultaneously be determined
What defines an orbital?
Region of space where where an electron is most likely to be located
What are the names of the four quantum numbers?
Principle, Angular momentum, magnetic, electron spin
How does the principle quantum number (n) define the nucleus and what values may it take?
Tells you how big the orbital is e.g. which shell the electron is orbiting in, values: 1 to infinity
How does the angular momentum quantum number (I) define the nucleus and what values may it take?
Tells you about the shape of the orbital, I value always 1 smaller than n value (n-1), stands for 3 sub shells, s (0) p (1) and d (2)
What shape is an s sub shell?
Spherical
What shape is an p sub shell?
figure of 8 shaped
What shape is an d sub shell?
like a 4 blade propellor
How does the magnetic quantum number (mi) define the nucleus and what values may it take?
Tells you the orientation of the orbital, s can only have one orientation, p has 3 -> px (-1), py (0) and pz (1) -> d-orbital -2 -> 2
What is the radial distribution function?
How probability of finding electrons varies from nucleus
What is a position around the nucleus where function = 0 called?
node
Why are 2 electrons allowed to occupy one orbital?
Due to different spin numbers, one spin up and one spin down electron is allowed
What is Hund’s Rule of Maximum multiplicity?
if 2 or more orbitals have same energy, then electrons will spread out to occupy maximum possible number of these, maximising number of parallel spins
What is spin correlation?
Parallel spins will stay further from each other to reduce electrostatic repulsion
What metal is present in , and vital for the function of Vitamin B12?
Cobalt, has 3 stable oxidation states close to one another, break Co-C bond diff. ways
At what point are a pair of atoms considered to have a chemical bond between them?
When atoms lie in ‘energy well’, have a lower potential energy than individual atoms
Define covalent bonding
Covalent bonding is when valence electrons are shared between 2 atoms
What is the octet rule?
Each atom shares electrons until it’s valence shell contains 8 electrons
What is a Resonance Hybrid?
Average lewis structure made from different resonance forms
What is a hypervalent compound?
A lewis structure which requires more than an octet of electrons e.g. PCl5
What are the basic assumptions of Valence shell electron repulsion theory (VSEPR)?
electrons from bonds/lone-pairs are considered as charge clouds, lowest energy arrangement = far apart as possiblee
What are further assumptions of the VSEPR theory?
lone pairs repel more than bonding pairs, multiple bond treated as single electron pair, lone pairs favour equatorial site
What importance does molecular shape have in biology?
enzyme active site, cell receptors, antibody/antigens
What are the limitations of VSEPR?
Cannot explain hyper valency or paramagnetism
What is Valence bond theory?
bonding orbital created by overlapping of 2 half filled atomic orbitals
What is hybridisation?
different atomic orbitals combining to give the same amount of equivalent hybrid orbitals
The hybridisation theory was proposed by which scientist?
Linus Pauling
What bond is formed in SP3 hybridisation?
Single bond, 3 types of bonding
What bond is formed in SP2 hybridisation?
Double bond, only 2 different types of bonding
Define a sigma bond
lie along line between atoms, symmetrical to rotation around bond, occur between s (and p and d) orbitals
Define a pi bond
overlap sideways on, not symmetric to rotation around the bond, occurs between p orbital
What are the benefits of valence bond theory over VSEPR?
Useful for discovering bond length/strength/force constant, acid base interactions, bond polarity
What are the issued of valence bond theory?
Still cannot explain paramagnetism in O2
What principle of electron behaviour does molecular orbital theory exploit?
Wave like nature of electrons, combinations of waves can be destructive/constructive, gives the bonding/antibonding orbitals
What denotes an anti bonding orbital?
A * sign
In an antibonding molecular orbital, is there 1 or 2 orbitals?
1, there is a node in the centre which causes orbital to look separate
After atomic orbitals have combined, is the bonding or anti bonding orbital of higher energy?
Antibonding orbital has a higher energy than bonding orbital and original orbitals
Will orbitals of different energies combine in the MO theory?
No, electrons must have the same angular momentum and principle quantum numbers
What suggest favourable bonding in MO theory?
Electrons are in lower energy state in bonding orbital than they were in atomic orbital
If there were equal numbers of electrons in the bonding and anti bonding MOs would a bond be favourable?
No, bonding would not be favourable because no energy gain having equal number of electrons in bonding/antibonding
What is the equation for bond order?
[(no. bonding electrons) - (no. antibonding electrons)]/2
What would a bond order of 0 suggest?
No bond favourable
What would a bond order of 1 suggest?
Single bond favourable
What effect would there be on the bonding/antibonding orbitals by a higher degree of overlap between atomic orbitals?
Bonding orbital would become lower, anti bonding orbital would become higher, bond strength would increase
What type of bonding does the pz orbital undergo in MO theory?
Sigma bonding
What type of bonding do the px and py orbitals undergo in MO theory?
Pi bonding
What does LUMO stand for?
Lowest unoccupied molecular orbital
What does HOMO stand for?
Highest occupied molecular orbital
How does MO theory show paramagnetism in O2?
Shows 2 unpaired electrons in 1 pi* orbital
Are covalent or non covalent bonds ‘highly directional’?
Covalent bonding is highly directional
Which of bonding (covalent/non-covalent) forms longer lasting, but shorter bonds?
Covalent
What type of bonding (covalent/non-covalent) can form inter and intra molecular bonds?
Non-covalent
What are the 6 types of non-covalent bonds?
London dispersion, Dipole-Dipole, Dipole-induced-Dipole, Ion-Dipole, Ion-Ion, Hydrogen
What symbol is used to represent polarity between atoms in VDW forces?
An arrow with a plus at the delta positive atom, and the arrow head faced toward delta negative atom
What causes polarity in a bond?
Electronegativity
How does electronegativity of atoms vary across a period?
Increases as you go across period (N is most electronegative)
How does electronegativity of atoms vary down a group?
Decreases as you go further down group
Is a high bond polarity likely to mean a covalent or ionic bond is formed?
Ionic
What is the overall molecular dipole moment (mu)?
The sum of individual bond dipole vectors in a molecule
Would dipoles of neighbouring molecules interact?
Yes, they would attract each other, gives rise to VDW forces
What’s the equation for the overall interaction energy between dipolar molecules?
E = -1/r^6 (r = distance)
What is a dispersion interaction?
Instantaneous dipole induces dipole in neighbour, dipoles attract
What is polarisability?
Ability of an atom to become polarised
Why does Br have a higher boiling point than Cl?
Br is more polarisable, so stronger dispersion interactions in neighbours
What is the dielectric constant otherwise known as?
Relative permittivity
What is the dielectric constant?
The ability of a material to store electrical energy when exposed to an electrical field, more polar molecules = higher dielectric con.
Is the dielectric constant a property of an individual atom or a bulk substance?
Bulk substance
What is the relationship between dipole moment, polarity and dielectric constant?
Greater dipole moment = more polar = higher dielectric constant
What happens to dipoles in hydration of ions?
Dipoles align in the field of the ion, lowers self energy of ion and stabilises
What is the definition of a hydrogen bond?
2 strongly electronegative atoms, one bound to a hydrogen and one with a lone pair of electrons -> short ranged, strong
Why does ice float on water?
When water freezes, molecules held apart by strong & stable H bonds -> further apart
What is the Grothuss Mechanism?
covalent and hydrogen bonds can interchange, causes charge transfer, no diffusion of H+
What is the benefit of the Grothuss mechanism?
Allows very fast conduction of H+ through water
What is the stationary phase in TLC?
SiO2 layer on plate (silicon dioxide)
What is another term for solute in chromatography?
Analyte
What is TLC used for?
Separating compounds based on their different bonding/polarities, stronger reactions= shorter distance travelled
What is the lifetime of a hydrogen bond?
1 - 10picoseconds (-12)
What is the collecting together of non-polar molecules known as?
The hydrophobic effect
Why does the hydrophobic effect occur?
Fewer ways of arranging hydrogen bond network when hydrophobic molecule added, reduces entropy, unfavourable for non-polar molecules to be surrounded by water - clump
Define an amphiphile
molecule which contains polar and non-polar areas (hydrophillic & hydrophobic)
