Topic 1.1 Atomic Structure

Question 1

Define Relative Atomic Mass (RAM)

Answer 1

The average mass of an atom of an element when measured on scale on which the mass of an atom of Carbon 12 is exactly 12.

Question 2

Define Relative Molecular Mass

Answer 2

The average mass of a molecule when measured on scale on which the mass of an atom of Carbon 12 is exactly 12.

Question 3

Define Relative Isotopic Mass

Answer 3

The mass of an atom of an isotope of an element measured on scale on which the mass of an atom of Carbon 12 is exactly 12.

Question 4

Why are all atoms neutral?

Answer 4

Because number of protons = number of electrons

Question 5

What did Dalton discover?

Answer 5

-Atoms are indivisible and indestructible particles
-Each element is made of identical atoms with the same mass, atoms are spheres

Question 6

What did JJ Thompson discover?

Answer 6

-Discovered the electron through the Cathode Ray experiment
-Proposed the plum pudding model (Electrons in a “positive pudding”)
-Atom is a sphere of positive charge

Question 7

What did Rutherford discover?

Answer 7

-Discovered the nucleus, most of atom is empty space
-Gold foil experiment: most Alpha particles passed straight through, showing most of the atom is empty space, some deflected showing a small positive nucleus

Question 8

What did Niels Bohr discover?

Answer 8

Proposed that electrons orbited the nucleus in fixed energy shells

Question 9

What did Chadwick discover?

Answer 9

Discovered the neutron, neutral particles in nucleus explain isotopes

Question 10

What is the function/purpose of Tof Mass spectrometry?

Answer 10

To identify elements by determining all the isotopes present in sample

Question 11

What are the key conditions needed for ToF Mass spec?

Answer 11

Must be kept under high vacuum otherwise air particles would ionise and register on detector

Question 12

Why must the sample be ionised in ToF mass spec?

Answer 12

So that the ions can be detected and attracted towards the negatively charged plate

Question 13

Give the details of Electrospray ionisation

Answer 13

1. Sample is dissolved in a volatile and polar solvent
2. Sample is injected at high pressure through a hypodermic needle giving a fine mist, tip of needle has high voltage
3. Each particle gains a proton as they leave the needle, solvent evaporates leaving behind positive ions
   -Represented by equation: M(g) + H+ —> MH+ (g)

Question 14

Give the details of Electron Impact

Answer 14

1. High energy electrons are fired at sample from an electron gun
2. This process knocks off 1 electron from each particle forming a 1+ ion
   -Represented by equation: Ti(g) —> Ti+(g) + e-

Question 15

What is electrospray ionisation used for?

Answer 15

Electrosray ionisation is used with larger organic molecules, this means fragmentation does not occur

Question 16

What is electron impact used for?

Answer 16

Electron impact is used for elements and substances with low formula mass, this causes fragmentation

Question 17

Explain what happens during Acceleration in ToF mass spec

Answer 17

The positive ions are accelerated to a constant kinetic energy by an electric field towards a negatively charged plate

Question 18

Explain what happens in the flight tube in ToF mass spec

Answer 18

-The velocity of each particle depends on its mass: lighter particles travel faster (have a faster velocity) whilst heavier particles have a slower velocity
-Ions are distinguished by different flight times: speed=distance/time

Question 19

Explain what happens in detection

Answer 19

The ions reach a detector (another negatively charged plate) and gain electrons which generates a current; size of current is proportional to abundance of species

Question 20

Define Aufbau’s principle

Answer 20

Electrons enter the lowest energy orbital available

Question 21

Define Hund’s rule

Answer 21

Electrons prefer to occupy orbitals on their own and only pair up when no empty orbitals of the same energy are available. This is because electrons in the same orbital repel

Question 22

Define Pauli’s exclusion principle

Answer 22

Two electrons in the same orbital must spin opposite ways

Question 23

Give the electronic configurations for Cr and Cu

Answer 23

Cr: 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5
Cu: 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d10

Question 24

What is key to remember when writing electronic configurations for ions?

Answer 24

Note that the 4s subshell is missed out

Question 25

Define ionisation energy

Answer 25

The amount of energy required to remove 1 mol of electrons from 1 mol of gaseous atoms

Question 26

Define first ionisation energy

Answer 26

The amount of energy required to remove 1 mol of electrons from 1 mol of gaseous atoms to form one mol of gaseous 1+ ions

Question 27

Define second ionisation energy

Answer 27

The amount of energy required to remove one mol of electrons from one mol of gaseous 1+ ions to form one mol of gaseous 2+ ions

Question 28

Define atomic radius

Answer 28

Distance from the nucleus to the outermost electron

Question 29

Define nuclear charge

Answer 29

Total charge of nucleus ( number of protons )

Question 30

What is electron shielding?

Answer 30

The repulsion between electrons in inner shells and outer electrons

Question 31

What is electron repulsion?

Answer 31

Pairing in the same orbital increases repulsion, this lowers ionisation energy as less energy is needed to remove an electron

Question 32

How does nuclear charge affect ionisation energy?

Answer 32

As nuclear charge increases, ionisation energy increases because more protons means there's a stronger attraction between the nucleus and outer electron therefore making it harder to lose an outer electron

Question 33

How does atomic radius affect ionisation energy?

Answer 33

As distance from the nucleus increases, ionisation energy decreases because greater distance = weaker attraction between nucleus and outermost electron

Question 34

How does shielding affect ionisation energy?

Answer 34

As shielding increases, ionisation energy decreases because there is a weaker attraction between the nucleus and outermost electron

Question 35

What is the general trend in ionisation energy across a period?

Answer 35

Ionisation energy generally increases due to increasing nuclear charge (more protons) whilst atomic radius decreases and shielding remains similar. This results in a stronger attraction between the nucleus and outermost electron.

Question 36

What is the general trend in ionisation energy down a group?

Answer 36

Ionisation energy generally decreases due to increased shielding and atomic radius meaning that there is a weaker attraction between the nucleus and outer electron. Increased nuclear charge is outweighed by increased shielding and atomic radius.

Question 37

Why do successive ionisation energies increase with ionisation number?

Answer 37

Because more energy is required to remove electrons from a more positive ion -Radius decreases and attraction between electrons and nucleus increases

Question 38

What do large jumps in successive ionisation energies show?

Answer 38

-Indicates removal of electrons from a new shell closer to the nucleus *This is used to deduce the group number of the element