Atomic Structure pt1

Question 1

Which letter is used to represent the atomic number of an atom?

Answer 1

Z

it is also the number of protons

Question 2

What does the atomic number tell us about an element

Answer 2

Number of protons in an atom

Question 3

What letter represents mass number

Answer 3

A

Question 4

How is mass number calculated

Answer 4

Number of protons + Number of neutrons= Mass number

Question 5

Define RAM (Relative Atomic Mass)

Answer 5

Average mass of all isotopes of an element compared to 1/12 of the mass of carbon 12

Question 6

Define isotope

Answer 6

Atoms with the same number of protons but different number of neutrons. (They still have the same chemical properties but different physical properties)

Question 7

How many orbitals and electrons do these letters contain

Answer 7

S-1 orbital-2 electrons
P-3 orbitals-6 electrons
D-5 orbitals-10 electrons
F-7 orbitals-14 electrons (this one will rarely be used)

Question 8

What would be the relationship between 2 electrons in the same orbital in terms of their spin

Answer 8

• Opposite spin
• Repel each other

Question 9

Explain why copper does not fit the trend for electronic configuration

Answer 9

it has one electron in its 4s orbital before filling 3d

This is the same for Chronium

Question 10

What happens in a time of flight mass spectrometer

Answer 10

1. Vacuum= The whole apparatus is kept under a high vacuum to prevent the ions that are produced colliding with air particles
2. Ionisation= Sample is ionised (either electron gun or electro spray)
3. Acceleration=The positive ions are attracted towards a negatively charged plate and accelerate towards it (Lighter ions and more highly charged ions achieve a higher speed)
4. Ion drift=Ions pass through a hole forming a beam and travel along a tube to a detector
5. Detection=the lighter ions are detected first as they have higher velocities. The positive ions pick up an electron from the detector which causes a current to flow
6. Data analysis= the signal from the detector is passed to a computer which generates a mass spectrum

Question 11

Why does the mass spectrometer need to be under a vucuum

Answer 11

Because the air particles would ionise and register on the detector

Question 12

When is electron impact used

Answer 12

For Elements or substances with low formula mass
It can also cause larger organic molecules to fragment

Question 13

When is electron spray used

Answer 13

For larger organic molecules

Question 14

True or false:
Fragmentation occurs in electrospray ionisation

Answer 14

False
It does not because the conditions are ‘softer’

Question 15

What is ionisation
(step 1)

Answer 15

The sample gets ionised( electrospray or electron impact)

Question 16

How is electron impact done(4)

Answer 16

• A vaporuised sample is injected at low pressure
• An electron gun fires high energy electrons at the sample
• Which knocks out an outer electron
• Forming positive ions with diff charges

Question 17

How is electro spray ionisation done (5)

Answer 17

• The sample is dissolved in a volatile, polar solvent
• It is then injected through a fine needle giving a mist or aerosol
• The tip of the needle has a high volatage
• At the tip of the needle,it gains a proton from the solvent in the form of a H+ ion X(g)+H^+–>XH+(g)
• The solvent evaporates whilst the ions move to the negative plate

Volatile- Flammable

Question 18

What is acceleration (step 2 )

Answer 18

When positive ions are accelerated by an electric field to a constant kinetoc energy

Question 19

Given that all the particles have the same kinetic enegry,Why do some particles go faster than others?

Answer 19

The velocity of the particls depends on its mass
Lighter particles have a faster velocity
Heavier particles have a slower velocity

Question 20

What is flight tube/ion drift(step 3)

Answer 20

• The positive ions with smaller m/z values will have the same kinetic energy as those with a larger m/z and will move faster
• Heavier ions take longer to move through the drift area
• The ions are distingushed by diff flight times

m/z= mass over charge

Question 21

Formula for time of flight

Answer 21

t=d/v
T= time of flight
d=length of flight tube
v=Velocity of the partciles

Question 22

What is detection(step4)

Answer 22

• Ions hit detector and this causes a current which causes electron flow
• The size of the current is proportional to tge abundance of the isotope

Question 23

Define Relative molecular mass (Mr)

Answer 23

Average mass of a molecule over 1/12 of the mass of a carbon 12

Question 24

What is the equation for an electron getting knocked off a sample

Answer 24

-x is just any element-
x(g)+e^- —> x^+(g) +2e^-

Question 25

What is the electron configuration for Cu

Answer 25

[Ar]4s^1 3d^10

Question 26

What is the electron configuration for Cr (chromium)

Answer 26

[Ar] 4s^1 3d^5

Question 27

For transition metals, when they are ionised which electron is removed fist in the sub shells? (only applies to d block elements)

Answer 27

the S block is removed first for example Fe is usually [Ar] 4s^2 3d^6
but Fe3+= [Ar] 3d^5

Question 28

What is the relative mass of an electron

Answer 28

1/1840