Section A 1 Flashcards
So we define a mole (mol) of a substance as containing …. molecules.
This value is …
6.022 x 10^23
Avogadros number, NA (or sometimes L)
M(Mg) = 24.31 x 1 g mol-1 = 24.31 g mol-1
This value is called the….. and it … units, in contrast to the relative ….., which ….
molar mass, M
has
molar (atomic) mass, Mr
is unitless
Using ….. the mass of the individual isotopes can be determined.
a mass spectrometer
Relative atomic mass is used to calculate ….
And the molar mass of a substance, M, is obtained by …..
relative molecular mass, Mr:
e.g. Mr(H2O) = (1.008 x 2) + (15.999 x 1) = 18.015
multiplying Mr by 1 g mol-1
e.g. M (H2O) = 18.015 x 1 g mol-1 = 18.015 g mol-1
This means that if we want to use 1 mol of water in the laboratory we would need 18.015 g.
No of mols (mol) =
mass (g) / molar mass (g mol-1)
An implication of describing the electron as a wave is the uncertainty principle –
its position and momentum (energy) cannot not simultaneously be determined.
Each electron in an atom is labelled with four quantum numbers. The first is….
It tells you about ….
the Principal quantum number:
n (the shell):
n = 1, 2, 3, …
how big the orbital is, or how far (on average) an electron
occupying it is from the nucleus.
The second quantum number is ….. :
This tells you about….:
the angular momentum quantum number: l
l = 0, … n-1
the shape of the orbital
l = 0 is an s orbital, l = 1 is a p orbital, l = 2 is a d orbital, etc.
The third quantum number is …. :
These are … orbitals, and tell you about ….
the magnetic quantum number: ml :
ml = -l, … +l
e.g. if l = 1, ml = -1, 0, +1.
the px, py, and pz
the orientation of the orbital
Wavefunctions can be used to calculate the radial distribution function of the orbital i.e. …
how the probability of finding the electron varies with distance from the nucleus.
The position where the function equals zero is called a ….and there is zero probability of the electron being found there.
node
the Pauli exclusion principle -
A maximum of two electrons can share each orbital, with the same values of n, l, ml but different spin (ms = +1/2 and -1/2).
Hunds Rule of maximum multiplicity -
If two or more orbitals have the same energy, then electrons will spread out to occupy the maximum possible number of these, maximising the number of parallel spins.
If the electrons occupy separate orbitals then they occupy different regions of space so there is …. electrostatic repulsion. This is a … energy arrangement.
less
lower
Why is cobalt essential for vitamin B12 function?
Vitamin B12 has an unusual Co-C bond which
can be broken three ways:
1. To form Co(III) and CH3-
(anion)
- To form Co(II) and CH3.
(rodnik) - To form Co(I) and CH3+
(kation)
Essential to its function that Co is stable in three oxidation states and they are relatively close in energy to allow fast conversion between them.
Przypomnienie:
Compounds which require more than an octet of electrons in order to draw a Lewis structure are called …..
Ans. hypervalent compounds.
Although period 2 elements obey the octet rule very well,
Period 3 elements begin to show some deviations.
e.g. PCl5 can only be explained if P has 10 electrons in its outer shell
In SF6 S must have 12 electrons in its outer shell
Znając: Number of electron pairs around central atom: 2
Podaj:
Shape:
Bond Angles:
Example:
Linear
180
BeF2
Znając: Number of electron pairs around central atom: 3
Podaj:
Shape:
Bond Angles:
Example:
Trigonal planar
120
BF3
Znając: Number of electron pairs around central atom: 4
Podaj:
Shape:
Bond Angles:
Example:
Tetrahedral
109.5
CF4
Znając: Number of electron pairs around central atom: 5
Podaj:
Shape:
Bond Angles:
Example:
Trigonal bipyramidal
90, 120
PF5
Znając: Number of electron pairs around central atom: 6
Podaj:
Shape:
Bond Angles:
Example:
Octahedral
90
SF6
Znając: Number of electron pairs around central atom: 7
Podaj:
Shape:
Bond Angles:
Example:
Pentagonal bipyramidal
90, 72
IF7
Structures based on tetrahedral geometry:
- No lone pairs
- One lone pair
- Two lone pairs
- Tetrahedral
- Trigonal pyramidal
- Bent
Structures based on trigonal bipyramidal geometry
- No lone pairs
- One lone pair
- Two lone pairs
- Trigonal bipyramidal
- Disphenoidal
- T-shaped
Structures based on octahedral geometry
- No lone pairs
- One lone pair
- Two lone pairs
- Octahedral
- Square pyramidal
- Square planar
Bond angles:
H20
NH3
CH4
HCN
CO2
Acetone
SF4
H2O:
e = 104.5 ‘bent’
NH3:
e = 107.3 ‘trigonal pyramidal’
CH4:
e = 109.5 ‘tetrahedral’
bond angle gets smaller due to lone pair repulsion (od dołu do góry)
HCN:
e = 180 ‘linear’
CO2:
e = 180 ‘linear’
Acetone
‘Trigonal planar’
SF4:
The F-S-F angle involving the axial F atoms is 173
Limitations of the Lewis model of bonding
It also does not explain some other observations, for example that the oxygen molecule is paramagnetic (it has unpaired electrons), which is not predicted by the Lewis model.
ATP is made up from three sections:
A purine base – Adenine
A pentose sugar – Ribose
A phosphate section - Triphosphate
Adenine + Ribose = Adenosine
These bonds are called pi or π-bonds. They have two …., above and below the line between the atoms.
lobes
Combinations of waves can either be constructive or destructive.
We use this argument when combining the s orbitals to from a bond:
If they combine constructively then electron density between the atoms is …… This is called ….
If the s orbitals combine destructively then electron density between the atoms is and this is called ….
increased
a bonding molecular orbital.
decreased
an anti-bonding molecular orbital.
Bond Order =
[(number of bonding electrons) – (number of anti-bonding electrons) ] /2
Bond order of:
1. He2
- H2
- He2 +
- So for He2: Bond Order = (2 – 2) / 2 = 0
A bond order of zero means there is no bond, so the He2 molecule does not exist. - H2 = (2 – 0) / 2 = 1
A bond order of 1 is equivalent to a single bond using the Lewis model, and is consistent with observations. - He2 + = (2 – 1) / 2 = ½
A bond order of ½ is something that is not encountered in
the Lewis electron pair model, but something that MO
theory can predict with ease.
What this means is that a bond of about half the strength
of a single bond can form between the He atoms of He2+
This means that this molecule can exist, but will not be
very stable. Its existence is likely to be transient.
Rozwiń skróty:
LUMO
HOMO
Lowest unoccupied MO (Molecular Orbital)
Highest occupied MO
