Fundamentals of chemistry

Question 1

Cathode ray tube

Answer 1

Cathode is negativley charged
Anode is positivley charged
electron flow from the cathode and are attracted to the anode
small holes in the anode create a beam of electrons - so electrons can behave as a wave

Question 2

Heisenberg uncertainty principle

Answer 2

It not possible to know both the position and velocity of an electron at the same time

Question 3

How can we prove that electrons act as a wave

Answer 3

If you have an electron moving along, and you put an object in the way with a small hole in it you will get curvatures behind the object. This is known as a DIFFRACTION pattern ( a property of waves) If you put an object with 2 holes in it you will also see a diffraction around both holes causing an interference pattern. If it were acting as a particle it would only be able to go through one hole.

Question 4

Hydrogen atomic orbitals - quantum numbers

Answer 4

n - energy levels - 1–
L - Assymetry of orbitals (0 - (n-1) )
m1 - degenracy of orbitals (-l - +l)
ms - electron spin (positive or negative)

Question 5

Pauli exclusion principle

Answer 5

No two electrons in an atom can have the same 4 quantum numbers, each orbital can accommodate two electrons one of each spin (ms)

Question 6

atomic orbital

Answer 6

orbital around one element

Question 7

Molecular orbital/bonding orbital

Answer 7

Orbital around a molecule eg 2 H atoms

Question 8

Orbitals in phase (Example Hydrogen)

Answer 8

also knowns as constructive interferance
leads to a bigger wave and forms a bond between the two hydrogen atoms leading to a bonding orbital. this is lower bonding than the anti-bonding orbital.

Question 9

Orbitals out of phase (example Hydrogen)

Answer 9

Leads to destructive interference which leads to a flat line. So there is no orbital between the two hydrogen atom (ie no bond ) this is called an anti bonding orbital. this is higher energy than the bonding orbital.

Question 10

What happens if another electron is added to H2

Answer 10

the electron is added to the anti-bonding orbital

Question 11

Bond order equation

Answer 11

Bond order = 1/2(number of electrons in bonding orbital - number of electrons in antibonding orbital)
a positive bond order indicates a stable bond and a bond order of zero indicates the molecule is unstable

Question 11

Molecular orbital theory

Answer 11

Bonding orbitals - Electrons in bonding orbitals stabilize the molecule
Anti bonding orbitals - Electrons destabilize the molecule as they are found on the outside region not between the nuclei

Molecular orbitals -

σ orbitals - formed by head on overlap ( 2s/2p)
𝜋 orbitals - formed by side on overlap of p orbitals (2p)
σ* - antibonding orbitals

Question 12

σ bond

Answer 12

• lower energy ie. more table
• 1st bond between 2 (C,N,O) atom is always a σ bond

Question 13

𝜋 bond

Answer 13

2nd/3rd bond between 2 atoms is always a 𝜋 bond
Will always be first bond to break

Question 14

Hybrid orbital

Answer 14

1st bond between 2 (C,N,O) atoms always involves a hybrid orbital

Question 15

p orbital

Answer 15

2nd/3rd bond between 2 atoms always involves a p orbital

Question 16

How long is a single bond

Answer 16

1.5 A
1A = 1x10^-10 m

Question 17

How long is a double bond

Answer 17

1.3 A

Question 18

How to identify sigma and pi bonds

Answer 18

single bond - Always 1 sigma bond
Double bond - 1 sigma + 1 pi bond
Triple bonds - 1 sigma + 2 pi bonds

Question 19

Resonance stabilisaton

Answer 19

Happens when electrons are delocalised in a ring structure so they move around the whole structure, so the structure can be presented in multiple ways. Eg in C4H4O the oxygen can become positively charged as the electrons move around.
IMPORTANT
When moving electrons in resonance connectivity(skeletal structure) cant change
only lone pairs and pi bonds can be moved

Question 20

What determines hybridisation

Answer 20

Shape

Question 21

sp2 - shape

Answer 21

trigonal - 120 degrees

Question 22

sp3 shape

Answer 22

tetrahedral - 109 degrees

Question 23

sp shape

Answer 23

linear - 180 degrees

Question 24

Partial bond meaning

Answer 24

it cant be rotated

Question 25

What bonds are strong sigma or pi bond

Answer 25

sigma

Question 26

Structural isomerism

Answer 26

same formula, different connectivity

Question 27

stereoisomers

Answer 27

Molecules with the same connectivities but different 3D shape

Question 28

Enantiomers

Answer 28

a molecule with a chiral centre and its mirror equivalent

Question 29

nomenclature of enantiomers

Answer 29

1. Priority of the atoms according to atomic number 2. if moving in a clockwise direction - R if moving in a anticlockwise direction - S

Question 30

How to seperate enantiomers

Answer 30

- retention of chiral centre - In solution enantiomers will take part in the same chemical reactions at same rate but if other molecule has a chiral centre the reaction rates and products can be different. This is important for enzymes as they have chiral centres so will react with one enantiomer but not the other

Question 31

dihedral angle

Answer 31

rotation around c-c bonds (angle between 2 planes)

Question 32

a plane

Answer 32

3 molecules make up a plane

Question 33

types of conformation

Answer 33

A) staggered - most stable (lowest energy) b) gauche c) eclipsed d) fully eclipsed - least stable (highest energy)

Question 34

Why is the staggered conformation more stable ?

Answer 34

Because in the eclipsed conformation have methyl groups closer together. This means the the electrons in the atomic orbitals repel each other so atoms that are not directly bonded cannot be too close.

Question 35

different conformations for cyclic molecules

Answer 35

Boat - less stable chair - more stable

Question 36

Different positions in a trigonal bypyramidal shape

Answer 36

Equatorial - atoms around the equator (preferred as less electron repulsion) Axial - atoms straight up and down

Question 37

Newman projection

Answer 37

loking down c-c bond

Question 38

fischer projection

Answer 38

used for sugars

Question 39

Howarth projection

Answer 39

rign and sugars in cyclic form