#atomic mass

[er-cryptid]

Patreon | Ko-fi

[katefishernyc]

Collaborative note-taking using GoodNotes to help a seventh grade student study for a science quiz on elements, compounds, and molecules.

[a-level-study-bunny]

MASS SPECTROMETRY (PART 1)

Mass spectrometry is a highly useful form of analysis, with the most commonly used type of mass spectrometry being time of flight (ToF) spectrometry. ToF spectrometry has multiple uses such as:

Finding out the relative atomic mass of an element by finding the mass and abundance of isotopes within the element

Finding out the relative molecular mass of a molecule

THE STAGES

There are multiple steps involved in the process and we need to know all of them (I know - I wish we didn't have to either but the AQA spec says so...)

Ionisation

Acceleration

Ion drift

Detection

1) IONISATION

There are actually two types of ionisation that we need to know that can happen in a ToF spectrometer. Electron impact ionisation (a.k.a. electron ionisation) and electrospray ionisation.

Electron impact ionisation (a.k.a. electron ionisation)

This process is done by first being vaporised and then bombarded with electrons that are fired from an 'electron gun' (i.e. a hot wire filament with a current that runs through it and emits electrons). This typically results in an electron being knocked off of each sample particle to form a 1+ ion. These 1+ ions are then attracted to a plate with a negative charge (this is where they're accelerated!) - However, this is a rather harsh form of ionisation and frequently results in fragmentation of the molecular ion (this results in fragments being picked up on the mass spectrum) - This is good to know, but also not actually in the specification! :)

Electrospray ionisation (this is a soft ionisation technique)

To start, the sample is mixed with a volatile solvent. This is then pushed through a hypodermic needle at high velocity. The needle has a high voltage held through it to shock the sample particles as they pass through. This results in a cloud of positively charged 1+ ions (they lose an electron because of the high voltage shock!) The ions are then accelerated by a negative plate.

2) ACCELERATION

The positive ions are accelerated using an electric field. This results in them all having the same kinetic energy. (Super important for the next stage!)

3) ION DRIFT

The +1 ions travel through the middle of a negatively charged plate (through a hole) into a tube. This is the stage where the ions drift through a field with no charge. The thing that differentiates these ions is their mass/charge ratio. The higher the mass/charge ratio, the heavier the ion, the slower it goes (and vice versa). This means they hit the detector at different times (thus showing the abundance - but I'll explain that in a moment!)

4) DETECTION

The 1+ ions hit a negatively charged plate. This contact causes the ions to lose their charge as they collect an electron from the plate. This results in a movement of electrons, which produces an electric current that we can measure. The more electrons that hit the plate at once, the larger the current. This then translates on the mass spectrum as a larger spike.

If you've made it this far, well done!! You deserve a cookie (or something... I don't have one for you, but you deserve one!!)

Now that you've looked at all of that, it's time to look at the results! But since this post is already rather long, I will be making another post to cover that! (Sorry!)

Useful AQA resources:

https://filestore.aqa.org.uk/resources/chemistry/AQA-7404-7405-TN-MASS-SPECTROMETRY.PDF - This has pictures etc and is official AQA material :D

[er-cryptid]

Patreon | Ko-fi  

[er-cryptid]

Patreon | Ko-fi  

[er-cryptid]

Patreon | Ko-fi

[whats-in-a-sentence]

Table 1.3 gives the range of atomic mass values for these ten elements, together with the conventional atomic masses which can be used when the source of the sample is unknown. (...) In this book, we will use the conventional atomic masses listed in table 1.3 in any calculations involving these ten elements.

"Chemistry" 2e - Blackman, A., Bottle, S., Schmid, S., Mocerino, M., Wille, U.

[ilearnedthistoday]

Is it possible to make a new element?

Is it possible to make a new element?

I learned this today. It is possible, but it is not easy, takes a lot of power, and the resultant element would not be very stable. There are 118 known elements that appear on the periodic table. The first 94 of them occur naturally on Earth and the other 24 are artificial. Scientists started to try to group elements together in the 18th century. Antoine Lavoisier grouped them into metals and…

View On WordPress