Week 1 Lectures

Question 1

Define elements

Answer 1

A substance that cannot be broken down to other substances by chemical reactions

Question 2

How many naturally-occurring elements are there?

Answer 2

92

Each one has a unique symbol, usually from the first one or two letters of the name, often from Latin or German

Question 3

Systems become as stable as possible to…

Answer 3

• minimise their energy and maximise their entropy

Question 4

How many elements are known to be essential for life?

Answer 4

About 25!

Four elements: carbon, oxygen, hydrogen, nitrogen - make up 96% of living matter

Question 5

Define atom

Answer 5

Smallest unit of matter which still retains the properties of an element

Question 6

Mass of proton and neutron =

Answer 6

1.66 x 10^-24 g

Question 7

What is atomic number

Answer 7

Number of protons

Question 8

Atomic mass

Answer 8

Sun of masses of all components (e, p, n)

Question 9

An isotope…

Answer 9

Different mass number, same atomic number

They all have exactly the same chemical properties ! (Chemically identical but different masses)

Question 10

Name 3 different types of atomic orbitals

Answer 10

1s —> 2 electrons
2s —> 2 electrons
2P —> 6 electrons (total - 2 in each)

Question 11

What is a compound?

Answer 11

A substance consisting of two or more elements on a fixed ratio

For example, table salt (NaCl) is a compound with equal numbers of chlorine and sodium atoms.

Question 12

List 4 different bonds

Answer 12

Covalent

Hydrogen

Ionic

van der Waal’s

Question 13

What is a covalent bond

What is the different between non-polar and polar

Answer 13

Sharing of electrons by two atoms

Polar covalent bonds are not equal sharing, while non-polar covalent bonds are equal sharing

Question 14

Hydrogen bonds form…

Answer 14

Molecules with polar bonds!

• they’re weak compared with covalent or ionic bonds. But are very strong when together
• they’re crucial to life on earth!

Question 15

Ionic bonds form when

Answer 15

Form when two atoms, very different in attraction for valence electrons come together.

A crystal is formed. (Between ions)

Question 16

van der Waal’s forces

Answer 16

Form between molecular substances such as non-polar and polar. Once formed, electrons tend to be stable!

• they’re very weak
• Strength = 0.5kJ/mole
• very short range
• collectively strong

Question 17

Formation of water molecule

Answer 17

Polar covalent bonds

Nucleus has slightly (delta) negative charge, so H has slightly positive charge

2 low e- pairs, where negative charge sits, not involved in bonding

2 e- shared with H, involved in bonding

Question 18

What is an orbital level?

Answer 18

A region of space an electron inhabits around the nucleus of an atom

Question 19

What is the code for a hybrid orbital?

Answer 19

SP^3
(3P orbital and 1S orbital together)

Where different orbital levels mix due to different energy levels

Question 20

Orbital shapes of the different level orbitals

Answer 20

S = Spherical shape around the nucleus
P = Dungbell shape
Hybrid = Balloon shape (combination of S and P)

Question 21

Electronegativity is?

Answer 21

The tendency of an atom to attract emectrons

Question 22

Water molecule shape?

Answer 22

Each bond is directed towards one corner of a tetrahedron (usually angle of 109.5°)

(Not shared electrons held closer to nucleus by O2)
Long pairs repel each other more than bonding pairs, reducing bond angle to 104.5°

2 lone pairs bond to the other H2O due to delta negative / positive attracting each other, and join via a hydrogen bond!

Question 23

Effect of hydrogen bonds in water: 1

Answer 23

Higher boiling point

Have to use energy to break collectively strong H bonds before vapour can be made

Question 24

Effect of hydrogen bonds in water: 2

Answer 24

Higher cohesion

Allows a whole column of water to travel up the xylem and into the leaf during transpiration
(Cohesion tension theory)

Question 25

Effect of hydrogen bonds in water: 3

Answer 25

High heat of vaporisation (Energy to convert 1G of water from liquid to gas at 25°) 580 calories (2426.72J) to convert 1G of water to a gas - meaning sweat cools us down as kinetic energy of water molecule left is reduced, so a cooling action occurs as energy is reduced/lost

Question 26

Effect of hydrogen bonds in water: 4

Answer 26

Ice floats Has a crystallised latis structure, (more open structure than water) so is less dense as bonds are held slightly further apart. Therefore in low temperature, ice floats so aquatic organisms can remain under the body of water… under the insulating layer!

Question 27

Effect of hydrogen bonds in water: 5

Answer 27

Higher surface tension Vamiscuous layer (dips in the middle, acts like skin) so insects and plant life can live a top of the surface!

Question 28

Effect of hydrogen bonds in water: 6

Answer 28

Higher specific heat capacity (Amount of heat absorbed or lost in order to alter the temperature of 1G of water by 1°) - water resists changing its temperature. Lots of energy is required to heat and cool hydrogen bonds to break or reform them! This bumps water temperature and allows a long time to cool/heat, which is an advantage for aquatic life!

Question 29

Effect of hydrogen bonds in water: 7

Answer 29

Water is a good solvent for polar molecules! Interact/react with any polar molecules such as alcohol! This is because O2 is electronegative, so it can interact with its lone pairs and bond to a positive bond

Question 30

Effect of hydrogen bonds in water: 8

Answer 30

Water is a good solvent for ionic compounds eg NaCl Anything that carries positive or negative charge can interact and be dissolved by a hydration shell!

Question 31

Hydration shell

Answer 31

A hydration shell is a structured arrangement of water molecules that surround an ion or a polar molecule when it dissolves in water based on its charge. If negative charge, water will angle towards it slightly positive If positive charge, water will angle towards it slightly negative

Question 32

Effect of hydrogen bonds in water: 9

Answer 32

Oil drop effect Water molecules next to the hydrophobic (non-polar) molecules cannot satisfy their H-bonding requirements so are less stable. To maximise number of H bonds which can be formed, clustering of non-polar molecules occurs!

Question 33

Why oil drop effect on water?

Answer 33

Can shake and it will mix for short period of time, but after long period of time it will separate! This is because it doesn’t like to be mixed with hydrophobic/non-polar molecules due to H bonds wanting to be as stable as possible so we end up with a cluster of non-polar molecules Did you know: This is why amino acids arrange themselves in such a way where hydrophobic region faces inwards and hydrophilic region faces outwards!

Question 34

Molecular mass =

Answer 34

Sum of masses of all atoms in a molecule (daltons)

Question 35

1 molecule of a compound always contains Avogadro’s number. What is this number?

Answer 35

6.02 x 10^23 molecules

Question 36

Anything in what symbol means concentration?

Answer 36

[ ] Square brackets

Question 37

What is pH?

Answer 37

A measure of ‘acidity’ (Or the concentration of protons (H+) present in an aqueous solution)

Question 38

What is the pH scale called?

Answer 38

Logarithmic scale from 1 to 14 1 extremely acidic (high [H+]) 14 extremely basic (low [H+])

Question 39

Features of Carbon compounds? (Organic chemistry)

Answer 39

Carbon has unique ability to form chains which are stable to air and water C bonds to 4 atoms (1s^2, 2s^2, 2p^2 - it needs to share 4 electrons from elsewhere) It’s tetravalent Nearly all molecules cells use to function are carbon based (DNA, protein, carbohydrate)

Question 40

pH equation

Answer 40

pH = -log([H+]) So, [H+] = 10^-pH

Question 41

Water dissociation constant (Pure water)

Answer 41

Kw = [H+] [OH-] = 10^-14

Question 42

How many atoms does C bond to?

Answer 42

4 It’s Tetravalent (Each carbon is tetrahedral if all carbons single-bonded)

Question 43

List functional groups of molecules involved in chemical reactions

Answer 43

Hydroxyl - form H bonds by donation or acceptance of H+ Amino - Sulphhydryl - disulphide bridge covalently links two cysteines Carbonyl - are reactive Carboxyl - important for protein formation; can donate proton into environment and will carry a negative charge Phosphate - formation of ATP or phosphate backbone

Question 44

What are isomers

Answer 44

Two organic molecules with the same number of atoms of the same elements but different structures

Question 45

Different types of isomerism

Answer 45

- structural: differ in covalent partners - geometric: differ in arrangement around a double bond - enantiomers: have identical physical and chemical properties (therefore very difficult to separate)

Question 46

What is an enantiomer

Answer 46

Molecules which differ only in spatial arrangement of groups around a central ‘asymmetric’ carbon atom They differ in the way they interact with other optically active compounds (They’re mirror images of one another - cannot be superimposed upon one another)