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Chemistry (W) > Atomic Structure > Flashcards

Atomic Structure Flashcards

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1
Q

What is the relative charge mass and position of a proton, neutron and electron?

A

Particle: Mass: Charge: Position:

Proton 1 +1 Nucleus

Neutron 1 0 Nucleus

Electron 0 -1 Shells

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2
Q

What force holds the protons and neutrons in the centre of the atom?

A

Strong nuclear forces

These are much stronger than electrostatic forces that hold electrons and protons together

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3
Q

Why do the protons in the Nucleus not repel each other?

A

The strong nuclear force overcomes the repulsion between protons

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4
Q

What is the atomic and mass number?

A

Atomic: no. of protons
Mass: no. of protons + neutrons

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5
Q

What are isotopes?

A

Atoms with the same no. of protons but a different no. of neutrons

They have the same atomic no but a different mass no

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6
Q

What is an ion?

A

A charged particle

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7
Q

What types of ions are metals and non- metals?

A

Metals: positive (cations)

Non-metals: negative (anions)

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8
Q

Why are the chemical reactions of isotopes of an element the same?

A

They have the same no. of electrons which affect chemical reactions

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9
Q

What physical properties may differ for different isotopes of the same element?

A

Different size of nuclei/ mass

Speed
Diffusion
Density
Bpt 
Mpt
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10
Q

What is the relative atomic mass?

A

The weighted average mass of an atom of an element compared to the mass of 1/12th of the mass of one atom of carbon-12

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11
Q

What is the relative isotopic mass?

A

The mass of an isotope compared to 1/12th of the mass of one atom of carbon-12

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12
Q

What is an orbital?

A

An energetically defined region around a Nucleus occupied by a single electron, or pair of electrons if they have opposite spin

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13
Q

What is a p block element?

A

An element whose atoms have their highest energy (outmost) electron(s) in a p-orbital

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14
Q

What is the first ionisation energy?

A

The energy needed to remove one electron from each atom of one mole of gaseous atoms to form one mole of gaseous ions with one positive charge

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15
Q

What can mass spectrometry be used to do?

A

Find the abundance and mass of each isotope in an element allowing us to determine the relative atomic mass

Find the relative molecular mass of substances made of molecules

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16
Q

What is a common form of mass spectrometry?

A

Time of flight mass spectrometry (ToF)

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17
Q

What is the first stage of time of flight mass spectrometry?

A

Ionisation

18
Q

What are the techniques of ionisation in ToF?

A

Electron impact

Electrospray ionisation

19
Q

How does electron impact work?

A

The sample is vaporised and then high energy electrons are fired at it
This usually knocks off one electron from each particle forming a +1 ion

20
Q

How are the electrons fired in electron impact?

A

From an electron gun which is a hot wire filament with a current running through it which emits electrons

21
Q

What is the general equation for electron impact?

A

X + e- —> X+ + 2e-

(g) (g)

22
Q

What happens to the +1 ions after electron impact?

A

They are accelerated by a negative electric plate as they are attracted to it

23
Q

What type of elements/substances is electron impact used for?

A

Ones with a low formula mass (can be inorganic or organic molecules)

24
Q

What happens in electrospray ionisation?

A

The sample is dissolved in a volatile solvent (eg water or methanol) and injected through a hypodermic needle to give a fine mist
The tip of the needle is attached to a positive high volt power supply
The particles gain a proton (a H+ ion) from the solvent as they leave the needle

25
Q

What is the general equation for electrospray ionisation?

A

X + H+ —> XH+

(g) (g)

26
Q

What kind of elements/substances is electrospray used for?

A

Substances with a higher molecular mass (including biological molecules like proteins)

27
Q

What is the problem with electron impact?

A

The molecular ion often breaks down into small fragments some of which are detected by the mass spectrum (fragmentation)

28
Q

Why are the positive ions accelerated using an electric field?

A

So they all have the same kinetic energy

29
Q

What is the equation for kinetic energy?

A

KE = 1/2 MV^2

30
Q

What is the equation for velocity of a particle?

A

V = spare root of 2KE/M

31
Q

What does the velocity of a particle depend on?

A

It’s mass (they have the same ke)
Lighter particles have a faster velocity
Heavier particles have a slower one

32
Q

What is the third stage of ToF?

A

Flight tube:
The +ve ions travel through a hole in the negatively charge plate into a tube
The time of flight of each particle through this flight tube depends on its velocity

33
Q

What is the equation for time of flight?

A

T = d/v

34
Q

What is the forth stage of ToF?

A

Detection:
The positive ions hit the negative detector plate and are discharged by gaining an electron from the plate
This generates movement of electrons and the electric current is measure
The size of the current gives a measure of the number of ions hitting the plate

35
Q

What does the mass spectrum show?

A

The mass to charge ration

Abundance of each ion that reaches the detector

36
Q

How can the relative atomic mass be calculated from mass spectrums?

A

combined mass of all isotopes

—

37
Q

Why may there be other peaks if electron impact is used?

A

Fragmentation caused by the break up of the molecular ion

38
Q

Where does ToF take place?

A

In a vacuum so no other particles interfere

39
Q

Which peak gives the molecular ion?

A

The furthest peak to the right

40
Q

What problems could be caused by ToF if the substances have the same masses?

A

Difficult to tell a molecule by mass spectrometry if they have the same Mr
They need to have chemical tests to confirm identification

Chemistry (W) (3 decks)

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