AS Chemistry Unit 1 : Section 1 - Atomic Structure

What are all elements made of?

atoms

What are all atoms made up of?

protons, neutrons, electrons

What takes up most of the volume of an atom?

The orbitals and the spaces between them

True or false : electrons are static outside in their energy levels outside the nucleus

False - they whizz around the nucleus in orbitals

Where is most of the mass of an atom located?

inside the nucleus - despite its diameter being 1/10000 of the whole atom

What is the relative charge of a proton?

+1

What is the relative charge of a neutron?

0

What is the relative charge of an electron?

-1

What is the relative mass of a proton?

1

What is the relative mass of an electron?

1/2000

What is the relative mass of a neutron?

1

What is the mass number?

the total number of protons and neutrons in a nucleus.

What is the atomic number?

number of protons in the nucleus

What is special about the proton number?

All atoms of the same element p have the same number of protons?

For a neutral atom...

the number of protons equals the number of electrons

How do you work out the number of neutrons?

mass number - atomic number

How do atoms from ions?

By gaining or losing electrons

Negative ions have \____ protons than electrons

less

Positive ions have \______ protons than electrons

more

What are isotopes?

atoms with the same number of protons but different number of neutrons

Do isotopes of the same element have the same chemical properties?

Yes , they have the same configuration of electrons , so they have the same chemical properties

Do isotopes of the same physical properties?

No - these differ slightly as they tend to depend on the mass of the atom

Give 2 examples of physical properties

Density , rate of diffusion , boiling point , SHC etc

What did John Dalton describe atoms as ?

Solid spheres that made up different elements

In 1897, what did J J Thompson Conclude from his experiments ?

An atom must contain even smaller , negatively charged particles - electrons. The solid sphere idea of the atom had to be changed

What was J.J. Thomson's model called?

Plum pudding model

Describe the plum pudding model

The plum pudding model suggested that an atom is a ball of positive charge with negative electrons in embedded in it

What experiment did Rutherford conduct?

Gold foil experiment

Describe the process of the gold foil experiment

They fired alpha particles (positively charged) at a thin sheet of gold

What did Rutherford expect to see based off the plum pudding model?

They expected to see most of the particles to be deflected slightly by the positive 'pudding' that made up the atom

What are the results of the gold foil experiment?

Most of the a,pua particles past straight through the ms and a very small number were deflected backwards. Therefore the Plum pudding model couldn't be right

What did Rutherford conclude? What did his new model consist off?

Most of the atom is empty space. His model consisted of a tiny positively charged nucleus at the centre surrounded by a cloud of negative electrons

What 4 basic principles did Niels Bohr propose with his new model:

1. Electrons only exist in fixed orbits (shells) and not anywhere in between

2. Each shell has a fixed energy

3. When an electron moves between shells electromagnetic radiation is emitted or absorbed

4. Because the energy of shells is fixed the radiation will have a fixed frequency

What did scientists after Bohr discover?

Not all the electrons in a shell had the same energy - they refined Bohrs model to include sub shells

What is the most accurate model of the atom we have today based on?

Quantum mechanics

What is the relative atomic mass?

The average mass of an atom of an element compared to one twelfth of the mass of an atom of carbon 12.

What is relative isotopic mass?

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

What is relative molecular mass?

The average mass of a molecule on a scale where an atom of carbon-12 is exactly 12

What 3 things can a mass spectrometer be used to find?

Relative atomic mass of elements

Relative molecular mass of compounds

Relative abundance of isotopes

What are the 4 stages of mass spectrometry

Ionisation, acceleration, ion drift, detection

What are the 2 ways of ionising a sample

Electrospray ionisation

Electron impact ionisation

Describe electrospray ionisation

The sample is dissolved and pushed through a small nozzle at high pressure. A high voltage is applied to it, causing each particle to gain a H+ ion. The sample is turned into a game made up of positive ions

What happens in electron impact ionisation?

The sample is vaporised and an 'electron gun' is used to fire high energy electrons at it. This knocks one electron off each particle, so they become +1 ions.

Describe the acceleration period during mass spectrometry

The positively charged ions are accelerated by an electric field so that they all have the same kinetic energy (this means that the lighter ions will end up moving faster than the heavier ions

What happens during ion drift?

The ions enter a region with no electric field , so they just drift through it. Lighter ions will drift through faster than heavier ions

Describe how a detector works

A detector records the different ions as they arrive at the detector. At the detector each positive ion gains an electron which generates a current. The size of the current is proportional to the abundance of each ion.

What happens during detection (mass spectrometry)

Because the ions that have a lower/mass charge ratio travel at higher speeds in the drift region, they reach the detector in less time than ions with a higher mass/ charge ratio. The detector detects charged particles and a mass spectrum is produced

ions with a lower mass/charge ratio travel through drift region at ..... speeds

higher

Ions with a higher mass / charge will take \__ time to reach the detector

More

Why must a vacuum be used during mass spectrometry?

We don't want the ions to collide with other particles in air

If electron impact ionisation was used how do you find the relative mass of an isotope from the mass spectrum

The mass / charge ratio of the peak is the same as the relative mass of that isotope

If electrospray ionisation was used how do you use the mass spectrum to find the relative mass of that isotope

A H+ ion would have been added to each particle to for, +1 ions so the mass charge ratio of each peak would be one unit greater than the relative mass of each isotope

What 3 steps must thou take to calculate the relative atomic mass from a mass spectrum

1. For each peak read the the % relative isotopic abundance from the y axis and the relative isotopic mass from the x axis . Multiply them together to get the total mass for each isotope

2. Add up these totals

3. Divide by 100 (as percentages were used)

What should you do if the relative abundance is not given as a percentage

The total abundance may not add up to 100 . Do steps 1 and 2 and then divide by the sum of the relative abundances

True or false: many elements only have 2 stable isotopes

False many elements only have 1 stable isotope

On a mass spectrum , what is on the y axis

% abundance of isotopes

On a mass spectrum, what should go in the x axis

Mass / charge

If the sample is an element what does each line represent (on a mass spectrum)

A different isotope of the element

explain how you can get a mass spectrum for a molecular sample

1) a molecular ion , M+ is formed in the mass spectrometer when one electron is removed from the molecule

2. This gives a peak in the spectrum with a mass/charge ratio equal to the relative molecular mass of the sample

3. This can be used to help identify an unknown compound

What is a molecular ion peak?

The peak with the highest m/z ratio in the mass spectrum - this represents the mass/charge ratio of the molecule being analysed

Electron shells are made up of...

sub-shells and orbitals

Electrons have \____ energies

Fixed

What is the number given to each shell called?

Principal quantum number

the further the shell is from the nucleus

the higher it's energy and the larger it's principal quantum number

True or false: Electrons in the same sub shell have the same energy

True

True or false : the sub shells in the same shell have the same energy

False : sub shells have slightly different energies

How many electrons can each orbital hold?

2 electrons

How many orbitals does an s sub shell have!

1

What is the maximum number of electrons in an s sub shell

2

How many many orbitals does a p sub shell have?

3

What is the maximum number of electrons in a p sub shell

6

How many orbitals does d have?

5 orbital

What is the maximum number of electrons in a d sub shell

10

How many rebuttals does an f sub shell have

7

What is the maximum number of electrons in a f sub shell

14

What is the maximum number of electrons in the first energy level

2 electrons

What is the maximum number of electrons in the second principal energy level?

8

What is the maximum number of electrons in the 3rd energy level?

18

What is the maximum number of electrons in the 4 th energy level?

32

Name all the sub shells in the 1 st energy level

1s

Name all the sub shells in the second energy level

2s 2p

Name all the sub shells in the third energy level

3s 3p 3d

Name all the sub shells in the 4th energy level

4s 4p 4d 4f

Electrons fill up the \____ energy sub shells first

Lowest

What are the 3 rules of electron configuration

1) electrons fill up the lowest energy sub shells first

2) electrons fill orbitals singly before they start sharing

3. For the configuration of ions from the s and p block of the periodic table, just remove or add electrons to or from the higher st energy occupied sub shell

What can you use for shorthand sub shell notation

Noble gases

Describe how chromium and copper are exceptions to electronic configuration rules

They donate one if their 4s electrons to the 3D sub shell, because they're happier with a more stable full or half full d sub shell

What else is unusual about transition metals (electron configurations)

When they become ions , they lose their 4s electrons before their 3d electrons