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7MRFFS01: Analytical Chemistry > Chemistry Catch-up > Flashcards

Chemistry Catch-up Flashcards

(75 cards)

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1
Q

Where are Proton, Neutrons and Electrons found within an atom?

A

Protons and Neutrons in the nucleus and Electrons orbit the nucleus in a 3D nature within shells

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2
Q

What is the Atomic orbital?

A

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

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3
Q

Tell me the structure of the atom?

A

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

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4
Q

Draw the s and p orbitals

A
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5
Q

What is the maximum number of electrons which can be found within each orbital?

A

2

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6
Q

What are orbitals grouped into and tell me the maximum capacity for each shell

How does the energy change across the shells

A

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

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7
Q

How is the periodic table arranged and what is this?

A

The periodic table is arranged by atomic number which is the sum of protons and electrons

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8
Q

The ground-state configuration is the atoms lowest energy state. For oxygen of atomic number 8, what is the ground-state electron configuration?

A

1s^2 2s^2 2p^4

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9
Q

What are the 3 rules which can be followed to predict the ground-state electron configuration?

A
  1. 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-)
  2. Only 2e- can occupy an orbital and must be of opposite spin
  3. 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)
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10
Q

Chemical bonding occurs in nature, what state do all systems seek and why is this the case?

A

All systems seek the lowest energy state because it is the most stable

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11
Q

How does chemical bonding occur?

A

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

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12
Q

What aspect of the periodic table represents the number of valence electrons an atom has?

A

The group number

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13
Q

Whats the octet rule?

A

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)

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14
Q

What do lewis dots represent?

A

The number of valence electrons

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15
Q

Valence e- redistribute to form bonds. Give some examples of the type of bonds that can form and how the electrons are distributed

A

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

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16
Q

Carbon is in group 14 (if include transition metals) and has an atomic number of 6. What is its ground state electron configuration?

A

1s2 2s2 2p2

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17
Q

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?

A

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)

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18
Q

However, explain the complications with carbon and how this is overcome

A

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

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19
Q

What occurs during hybridisation and what are the orbitals which are formed called?

A

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

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20
Q

Tell me about sp^3 hybridisation and the angles?

A

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

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21
Q

Tell me about sp^2 and sp hybridisation

A

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

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22
Q

When does a** molecular bonding orbital** form?

A

When two atoms share a pair of valence e- they overlap and form molecular bonding orbitals

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23
Q

What are the two types of overlapping bonding orbitals?

A

Sigma and Pi

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24
Q

Can Pi bonds rotate?

A

No, as they are located above and below the plane and if they rotate then they will break the bond

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25
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
26
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
27
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
28
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**
29
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
29
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
30
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
31
What is needed for conjugation to occur?
at least 3 p orbitals in a row
32
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-)
33
VSEPR
34
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
35
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)
36
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
37
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**
38
Tell me about ion-dipole forces
Interaction between **charged ion** and**polar molecule** e.g. water and NaCl Cations- negative end of dipole Anions- positive end of dipole
39
Tell me about dipole-dipole forces
Interaction between **neutral polar molecules** Permanent dipoles Weaker than ion-dipole forces
40
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
41
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
42
What does bond polarity depend on?
The electronegativity difference between atoms
43
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
44
What is the polarity of the isomers cis- and trans-dichloroethene?
Cis-dichloroethene= polar trans-dichloroethene= non-polar
45
Whats the polarity of CO2?
Non-polar The dipoles cancel each other out
46
Whats the polarity of H2O?
Polar The tetrahedral shape of water names that the polarity doesnt cancel out
47
How is a solution produced?
A **solvent** is a substance that can dissolve a solid, liquid or gaseous **solute** producing a **solution**
48
What is solubility?
How well a solute dissolves in a particular solvent solvent= water organic solvent= methanolor hexane
49
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)
50
How can the polarity of a solvent be measured?
By the dipole moment or their dielectric constant
51
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
52
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
53
Whats the **Partition coefficient**?
2 immidible solvent: 1 hydrophobic and 1 hydrophilic
54
Tell me values of logP for: Polar/ hydrophilic and Non-polar/hydrophobic
Polar/ hydrophilic= lowest logP values Non-polar/ hydrophobic= highest logP values
55
Name some different functional groups
* Alkanes * Alkenes * Alkynes * Aromatics * Alcohols * Aldehydes * Ketones * Carboxylic acids * Amides * Amines * Ethers * Esters * Phenyl/ arene
56
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)**
57
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
58
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)
59
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
60
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+)
61
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
62
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
63
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
64
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)
65
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+)
66
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 basic**as LP e- conjugated with carbonyl
67
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
68
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
69
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]
70
How does PKa relate to acid strength?
The lower the PKa= stronger acid The larger the PKa= The stronger the conjugate base
71
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
72
For acidic/ basic compounds what is polarity effected by?
The pH of solution More polar in ionised state
73
LogP values are not useful for polarity as it doesnt take into account the ionised state. What would we use instead?
LogD= log (([Unionised](0)/[unionised](aq))+[ionised](aq))
74
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7MRFFS01: Analytical Chemistry (13 decks)

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