SECTION H Flashcards
What is nuclear fusion? Why does it require a lot of energy?
A process that takes place when two or more atomic nuclei collide and join to form a new type of atomic nucleus.
A lot of energy is needed to overcome the repulsion between the nuclei.
What elements are “chosen” for biological systems and why?
Lighter, readily available elements (most abundant)
What 3 characteristics must a biological element have?
- It must have a useful function
- It must be abundant in the environmnet
- It must be in an easily extractable form
What is the first ionisation energy?
Energy required to remove the most loosely held electron from one mole of gaseous atoms to produce 1 mole of gaseous ions each with a charge of +1
X(g) —-> X+(g) + e-
What is the nuclear charge?
It is the total charge of all the protons in the nucleus.
What is the trend in ionisation energies in the periodic table?
Increase as we go to the right in periods, decrease as we go down in groups.
Why do ionisation energies increase across a period?
Elements in the same period —> same valence orbital
Electrons in the same orbital are poorly shielding of the added nuclear charge that comes with additional protons in the nucleus as we go across a period.
Thus, the effective nuclear charge experienced by the valence electrons is greater as we go across a period and the ionisation energy increases (electrons are held more tightly by the nucleus)
Why do ionisation energies decrease as we go down a group?
Going down a group —> atomic radius increases
The valence electrons are further away from the nucleus and thus experience less effective nuclear charge as they are shielded by the electrons in other orbitals
Consequently, they valence electrons are less tightly held and easier to remove
What is electronegativity and what trend does it follow?
It is a chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself.
Increases across a period and decreases down a group (same as ionisation energies)
How can the oxidation state of an atom in a molecule be determined?
The sum of all the oxidation states of the constituent atoms in a molecule must be equal to the overall charge on the molecule
What is a Lewis acid?
Electron pair acceptor. It must have a vacant molecular obrital in which to accept the pair of electrons. They are electron deficient.
examples:
H+ , BH3, AlF3, SF4
What is a Lewis base?
Electron pair donor.
Donation of electrons comes from a filled molecular orbital.
examples:
H-, NH3, PMe3, F- , H2O
All have a pair of electrons not used in bonding, generally a lone pair.
Why is KMnO4 widely used as an oxidisng agent?
Mn (vii) ion is easily reduced to Mn (ii)
What is a stability constant? (in this context)
Equilibrium constant (K) that defines the position of the equilbrium in an acid-base interaction.
The position of such equilibrium can be used to classify LA and LB as hard or soft.
What is synergic bonding?
Some molecules can simultaneously act as a LA or a LB.
These molecules have a high lying filled orbital and a low lying unfilled orbital. This is the case for a number of ligands such as CO, found in hydrogenases.
