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
Conjugated systems give rise to strong colours, why?
- Caused by e- in system absorbing photons
- Light absorbing property is the basis of chromophores
- Chromophores allow us to quantify using UV/Vis spec
What is needed for conjugation to occur?
at least 3 p orbitals in a row
What determines molecular shape?
The Valence shell electron pair repulsion theory (VSEPR)
The groups of e- surrounding the atom are -ve, so repel each other
The e- try to get as far apart from each other as possible
Groups of e- include bonding and non-bonding e- (e.g., Lone pair e-)
VSEPR
What are the different types of intermolecular forces?
- Ion-dipole forces
- Dipole-Dipole interactions (Van der waals)
- Instantaneous induced dipole (van der waals)
- Hydrogen bonding
If an atom has a high electronegativity, what does this mean?
It has a greater pull e.g. F,O N (decreased shielding, larger nucleus)
Bond polarity differs depending on the electronegativity between different atoms. Tell me the polarity of the different bond types
**Completely non-polar **
* covalent bond
* equal share of e- e.g., N2,Cl2,O2
**Polar covalent **
* covalent bond
* unequal share of e-
Completely polar
* Ionic bond
* one ‘takes’ e- from another
The electronegatibity increases from non-polar –> polar
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 ion-dipole forces
Interaction between charged ion andpolar molecule e.g. water and NaCl
Cations- negative end of dipole
Anions- positive end of dipole
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
What does bond polarity depend on?
The electronegativity difference between atoms
C and H have similar electronegativities and their bond is considered non-polar
Unsubstituted hydrocarbons considered non-polar molecule
For other polyatomic moleucles we must consider what?
- The EN of the bonding atoms
- The dipole moments
- The direction of the dipole moment- the direction of the bond
What is the polarity of the isomers cis- and trans-dichloroethene?
Cis-dichloroethene= polar
trans-dichloroethene= non-polar
Whats the polarity of CO2?
Non-polar
The dipoles cancel each other out
Whats the polarity of H2O?
Polar
The tetrahedral shape of water names that the polarity doesnt cancel out
How is a solution produced?
A solvent is a substance that can dissolve a solid, liquid or gaseous solute producing a solution
What is solubility?
How well a solute dissolves in a particular solvent
solvent= water
organic solvent= methanolor hexane
What should a solvent be?
Inertand not react with the solute
They are commonly classified as polar (e.g.,water) or non-polar (e.g., hexane)
How can the polarity of a solvent be measured?
By the dipole moment or their dielectric constant
How does the dipole moments and dielectric constants vary between polar and non-polar solvents?
Polar solvents
* Large bond dipole
* Large dielectric constant
* e.g.,water=80
Non-polar solvents
* Lack dipole moment
* small dielectric constant
* e.g.,hexane=2
* aliphatic and aromatic hydrocarbons
What is the general rule of solubility?
“like dissolves like”
* Non-polar solvents dissolves non-polar compounds
* Polar solvents dissolve polar compounds (due to intermolecular interactions formed)
* Polar solvents are immisicble with non-polar solvents
Whats the Partition coefficient?
2 immidible solvent: 1 hydrophobic and 1 hydrophilic
Tell me values of logP for: Polar/ hydrophilic and Non-polar/hydrophobic
Polar/ hydrophilic= lowest logP values
Non-polar/ hydrophobic= highest logP values
Name some different functional groups
- Alkanes
- Alkenes
- Alkynes
- Aromatics
- Alcohols
- Aldehydes
- Ketones
- Carboxylic acids
- Amides
- Amines
- Ethers
- Esters
- Phenyl/ arene
Tell me about Alkanes and Alkenes
- Saturated hydrocarbons
Alkanes –> CnH2n+2
single C-C bond - Unsaturated hydrocarbons
1, 2 or 3 C-C bonds
Alkenes –> CnH2n (double bond)
Alkynes –> CnH2n-2 (triple bond)
What are the characteristics of an alkane?
- Each carbon has a sp^3 hybridisation
- Free rotation around the C-C bond
- Similar EN between C and H, Non-polar
Tell me about HPLC with alkanes
- Liquid mobile phase pumped through a column containing a stationary phase
- separation is based on interactions with a stationary phase
- C18 is a common non-polar stationary phase (important to prime column first with non-polar solvent due to the free rotation of C bonds, this straightens out the chains to allow interactions to form with what is being analysed as opposed to itself)
Tell me about the characteristics of alkenes
- Contain C=C
- carbon atoms are Sp^2 hybridised
- Three sp^2 hybrid orbitals form 3 sigma bonds
- remaining p orbital on each C overlap to form Pi bond
- C=C cannot rotate
What hybridisation is seen between alkanes, alkenes and alkynes and how does the s and p character vary and what does this mean?
Alkanes- sp^3
Alkenes- sp^2
Alkynes-sp
Decrease in p character down list
Increase in s character down list
- more s character means e- held tighter and less likely to be shared: more acidic and therefore easier to donate a proton (H+)
- More p character increases shielding of nucleus: more basic which means easier to accept a proton (H+)
What are the characteristics of alcohols?
- Hydroxyl group
- Primary:RCH2-OH
Secondary:R2CH-OH
Tertiary:R3C-OH - -OH is polar so miscible in water
- C-C is non-polar and resists solubility
Short chain alcohols are soluble in water
Long chain alcohols are not soluble in water
What are the characteristics of phenols
- hydroxyl groups attached to aromatic rings are phenols
- more acidic than alcohols as -ve charge can be delocalised in aromatic ring
What are the characteristics of aldehydes and ketones
- ketone is in middle of chain
- aldehyde in end of chain
- C=O has permanent dipole because it is a form of dipole-dipole interaction
What are the characteristics of carboxylic acids
- The carbonyl and hydroxyl groups modify each other
- C=O has a permanent dipole: pulls e- away from H in OH group –> makes carboxyl group acidic (-H+) as can easily donate a proton due to stability of carboxylate anion RCOO- (This is not the case for alcohols as they are not acidic)
Whats the characteristics for amines?
- derived from ammonia -NH3
- Number of R groups on the nitrogen
- Primary: RNH2
Secondary: R2NH
Tertiary: R3N - like ammonia, they are tetrahedral sp^3
- they are weak bases that accept a proton (H+)
What is the characteristics for amides?
- Carbonyl group (C=O) linked to N atom
- Primary:R’ and R”= H
Secondary:R’ or R”= H
Tertiary:R’ and R”= Not H - Not basicas LP e- conjugated with carbonyl
Whats the characteristics of ethers and esters?
- Ethers: oxygen atom is connected to two alkyl or aryl (aromatic groups)
- Esters: Carbonyl group joined to the oxygen atom attached to alkyl or aryl group
Whats the equation for acid + base?
What is the role of each component?
AH (acid) + B (base) <–> BH^+ (conjugate acid) + A^- (conjugate base)
acid/ conjugate acids can donate protons, H+
bases/ conjugate bases can accept protons, H+
acids are proton donors and bases are proton acceptors
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]
How does PKa relate to acid strength?
The lower the PKa= stronger acid
The larger the PKa= The stronger the conjugate base
What is acid strength dependent on?
The stability of the conjugate base
e.g.,
Carboxylic acids roughly Pka=5
Phenols roughly PKa= 10
Alcohols roughly PKa= 15
The difference in acid strength is down to delocalisation
For acidic/ basic compounds what is polarity effected by?
The pH of solution
More polar in ionised state
LogP values are not useful for polarity as it doesnt take into account the ionised state. What would we use instead?
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