Chemistry Catch-up Flashcards
Where are Proton, Neutrons and Electrons found within an atom?
Protons and Neutrons in the nucleus and Electrons orbit the nucleus in a 3D nature within shells
What is the Atomic orbital?
A region of space around the nucleus where the electron is most likely to be found.
Electrons can be anywhere within this orbital but cannot be found outside it
Tell me the structure of the atom?
There can be up to 4 different orbitals which are termed s, p, d and f
Note: only s and p are relevant for this module
Draw the s and p orbitals
What is the maximum number of electrons which can be found within each orbital?
2
What are orbitals grouped into and tell me the maximum capacity for each shell
How does the energy change across the shells
Orbitals are grouped into shells.These shells contain different numbers of orbitals
Shell 1: 1s (2e-)
Shell 2: 1s 3p (8e-)
Shell 3: 1s 3p 5d (18e-)
The energy of the shells increases as you move out from the nucleus
How is the periodic table arranged and what is this?
The periodic table is arranged by atomic number which is the sum of protons and electrons
The ground-state configuration is the atoms lowest energy state. For oxygen of atomic number 8, what is the ground-state electron configuration?
1s^2 2s^2 2p^4
What are the 3 rules which can be followed to predict the ground-state electron configuration?
- Orbitals of lowest energy are filled first according to order
1s^2 (2e-)
2s^2 2p^6 (8e-)
3s^2 3p^6 3d^10 (18e-)
4s^2 4p^6 4d^10 4f^14 (32e-) - Only 2e- can occupy an orbital and must be of opposite spin
- If two or more empty orbitals of equal energy are available, one e- occupies each with spins parallel until all orbitals are full (as seen in image)
Chemical bonding occurs in nature, what state do all systems seek and why is this the case?
All systems seek the lowest energy state because it is the most stable
How does chemical bonding occur?
Bonds form due to Valence electrons
Valence electrons occupy the shell furthest from the nucleus and is what is encountered first when within close proximity
Rearrangement and redistribution enables a stable interaction and drives chemical bonding
What aspect of the periodic table represents the number of valence electrons an atom has?
The group number
Whats the octet rule?
The most stable atoms have full valence shells
The octet rule is that 8 valence electrons are needed to fill a shell (Note: ignore when dealing with atoms of an atomic number <20)
What do lewis dots represent?
The number of valence electrons
Valence e- redistribute to form bonds. Give some examples of the type of bonds that can form and how the electrons are distributed
Ionic: one or more atom are transferred from one atom to another
Polar covalent
Covalent: One or more pairs of atoms are shared equally
The ionic character decreaes from covalent to ionic bond
Carbon is in group 14 (if include transition metals) and has an atomic number of 6. What is its ground state electron configuration?
1s2 2s2 2p2
Carbon has 4/8 electrons in the valence shell (shell 2). Keeping this information in mind, how many bonds does carbon want to form and what state does it need to be in for this to work?
Carbon wants to form 4 bonds
In the ground state carbon has 2 un-paired e-
In the excited state, when bonding, carbon gains energy to unpair the 2s electrons –> 4 unpaired electrons (valency of 4)
However, explain the complications with carbon and how this is overcome
The s and p orbitals are different shapes with s being spherical and p being dumbell shaped
the s and p orbitals therefore have different energies with s orbitals < p orbitals which is why s is filled first
However…
the 4 bonds of methane for example are identical and spatially orientated towards the corner of the tetrahedron
any H atom can be removed from the C atom with equal ease
carbon forms 4 bonds using 4e- of identical energy that are indistinguishable from each other
This is explained using hybridisation
What occurs during hybridisation and what are the orbitals which are formed called?
The blending of the 2s orbital with the three 2p orbtials to produce 4 identical orbitals
because these orbitals are made from both s and p orbitals it forms a sp^3 hybrid orbitals
all hybrid orbitals are identical and form identical bonds
Tell me about sp^3 hybridisation and the angles?
sp^3 orbitals are of a different shapeto that of s or p
They are angled towards the corners of a regular tetrahedron
It is the most stable configuration because the e- are as far apart as possible
Tell me about sp^2 and sp hybridisation
Not essential for carbon to have all 4 unpaired electrons hybridised
hybridisation with the 2s and the two 2p orbitals results in 32p^2 hybrid orbitals
Forms a trigonal planar structure
sp hybrid orbitals derived from the 2s and one 2p orbitals are linearly opposed
When does a** molecular bonding orbital** form?
When two atoms share a pair of valence e- they overlap and form molecular bonding orbitals
What are the two types of overlapping bonding orbitals?
Sigma and Pi
Can Pi bonds rotate?
No, as they are located above and below the plane and if they rotate then they will break the bond
What bonding is found in single bonds?
sigma bonds
In methane, due to hybridisation,there are sp^3 hybrid orbitals present. These orbitals will overlap to form sigma bonds
single C-C bonds can also form between two sp^3 orbitals
What bonding is found in double bonds?
Carbon is sp^3 hybridised
One remaining unpaired e- in a 2p orbital
sigma bonds formed by 2p^2 orbitals from C, and s orbitals from H, or two adjacent sp^2 orbitals (C-C)
These p orbitals can overlap to form Pi bonding
Tell me about the bonding present in benzene
Each C atom forms three sigma bonds and has one unshared valence electron in a p orbital
These p orbitals are on adjacent C atoms and therefore overlap
This forms an unusual Pi orbital
This Pi orbital takes the form of two doughnut shaped rings above and below the benzene ring
The electrons in benzene are described as being delocaised, tell me about this
The electrons can move anywhere within the Pi bond and are said to be delocalised
The delocalisation means that the bonds between the carbon atoms are halfway between being in single and double bonds and form a conjugated system
P orbitals which overlap to form conjugated systems can occur in what else?
Can also occur in non-aromatic systems
e.g., The carrot pigment Beta-Carotene which is linear as opposed to a ring
It has lots of alternating single and double bonds and an extensive network of conjugated bonds
P orbitals which overlap to form conjugated systems can occur in what else?
Can also occur in non-aromatic systems
e.g., The carrot pigment Beta-Carotene which is linear as opposed to a ring
It has lots of alternating single and double bonds and an extensive network of conjugated bonds
VSEPR
What is a dipole?
An unequal sharing of electrons
Skewed towards the most electronegative atom
The difference between the EN is known as a dipole moment
Tell me about dipole-dipole forces
Interaction between neutral polar molecules
Permanent dipoles
Weaker than ion-dipole forces
Tell me about induced dipole interactions
Van der waal force:
* interaction between all covalent molecules
* dipoles are induced
* very weak- atoms have to be close together
Tell me about hydrogen bonding
Requires…
* Hydrogen atom bonded to an electronegative atom (e.g., N-H, O-H or F-H)
* electronegative atom with lone pair e- (e.g., O, N or F)
* Partial positive charge on H is attracted to lone pair of a nearby electronegative atom
* The strongest intermolecular interaction is when H atoms have no inner core of electrons shielding the nucleus
Whats the Partition coefficient?
2 immidible solvent: 1 hydrophobic and 1 hydrophilic
Whats the PH equation which involved PKa?
If pH > PKa, more are deprotonated (A- or B); [proton acceptors] > [Proton donor]
If pH < PKa, more are protonated (AH or BH+)
[Proton acceptor] < [proton donor]
