Topic 1- Atomic Structure

Question 1

What is an electrostatic force?

Between what sub atomic particles is the electrostatic force between in an atom?

What are the relative masses of the following sub atomic particles:

Protons

Neutrons

Electrons

What are the relative charges of the following sub-atomic particles:

Protons

Neutrons

Electrons

Answer 1

An attraction between a positive and negative charge

In an atom, the electrostatic force is between the protons (+) and electrons (-)

1

1

1/1836 (AKA negligible mass)

+1

0

-1.

Question 2

What did John Dalton believe about the atomic model of an atom at the start of the 19th century?

What did J.J.Thompson (1897) conclude that an atom must contain?

Describe the three things that occurred in Earnest Rutherford’s experiment in 1909?

What did Rutherford propose and describe?

What four things did Niel Bohr propose?

Answer 2

John Dalton described atoms as solid spheres and different spheres made up different atoms

Smaller negatively charged particles- called electrons

• He fired (positive) alpha particles at gold foil
• Expecting most of alpha particles to be deflected slightly but most passed straight through
• Few alpha particles were deflected by the positively charged nucleus concluding a lot of empty space

The nuclear model, that there was a tiny charged positive nucleus at the centre surrounded by a cloud of negative electrons

• Electrons exist in fixed orbits (shells)
• Each shell has a fixed energy
• When an electron moves between shells electromagnetic radiation is emitted or absorbed
• Because energy of shells is fixed, radiation will have a fixed frequency.

Question 3

What happens as electrons move between shells?

What also happens as electrons move between shells?

What can each shell or energy level hold?

Where are the protons and neutrons in an atom?

How are these two sub atomic particles held together by?

Answer 3

Electromagnetic radiation emitted as electron moves between shells

Electromagnetic radiation absorbed as electron moves between shells

A maximum number of electrons

In the centre of the atom, called the nucleus

A force called the strong nuclear force.

Question 4

What is the maximum number of electrons for each of these shells:

1st Shell

2nd Shell

3rd Shell

4th Shell

5th Shell

What is the formula for the maximum number of electrons in each shell, if n is the number of shells?

Answer 4

2

8

18

32

50

2n squared (n being the number of electrons).

Question 5

What is the atomic number (Z) of an element?

What is atomic number also known as?

What is the mass number (A) of an element?

What two things are equal in numbers in an atom?

Therefore what does this mean concerning atomic number?

What is the definition of an isotope?

What is the preferred a-level exam definition of an isotope?

What are the chemical properties of isotopes?

Why is this?

What are the physical properties of isotopes?

Answer 5

Number of protons in the nucleus of an atom

Proton number

Sum of the protons and neutrons in the nucleus

In an atom, the number of protons always equals the number of electrons

In an atom, the atomic (proton) number is the same as the number of electrons

Atoms with the same atomic number but different mass number

Atoms with the same number of protons but a different number of neutrons

The chemical properties of isotopes are identical

This is because they have the same electronic configuration

The physical properties of isotopes can differ (such as density).

Question 6

What are the two uses of time of flight spectrometry?

What are the four stages of time of flight spectrometry?

What will always happen to the sample that goes in?

What are the two types of ionisation called and describe when used?

Answer 6

• Find the abundance and mass of each isotope in an element allowing us to determine its relative atomic mass
• Find the relative molecular mass of a substance made of molecules
• Ionisation
• Acceleration
• Flight tube
• Detection

The sample that goes in will always become a positive ion

• Electron impact ionisation: for elements and substances with low formula mass
• Electrospray ionisation: for substances with high molecular mass

Question 7

What are the four stages of electron impact ionisation?

What is the ionic equation for electron impact ionisation?

How are the particles ionised in electrospray ionisation?

What does this then form and explain these?

What is the ionic equation for electrospray ionisation?

What are the positive ions accelerated by in stage 2 of Time of Flight Mass Spectrometer?

What do all the ions have during this stage?

Which ions experience a greater acceleration?

Why is this?

What is the formula for kinetic energy?

What is mass of the particle measured in?

What is the velocity of the particle measured in?

What is the formula for velocity using kinetic energy formula?

Answer 7

• Sample vaporised
• High energy electrons are fired at it from an “electron gun”
• Usually knocks off one electron from each particle forming a 1+ ion
• 1+ ions attracted towards a -ve electric plate where they are accelerated

X(g)—> X(+) (g) + e(-)

Ionised by gaining a proton (H+ ion) from the solvent

XH+ ions (ions with a single positive charge and a mass of Mr +1)

X(g + H+ —-> XH+ (g)

Accelerated by an electric field

All the ions have the same kinetic energy

Ions with a lower mass/charge ratio experience a greater acceleration

They are lighter so they accelerate more

KE= 1/2 m v2

Measured in kg

ms-1

v= square root 2KE -:- m.