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The Sub-atomic particles

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Introduction

Foundation Chemistry The Sub-atomic particles Atoms are made of three main particles: protons, neutrons and electrons. > The protons and neutrons form the nucleus, in the centre of the atom > Protons and neutrons are sometimes called nucleons, because they are found in the nucleus. > The electrons surround the nucleus Properties of the sub-atomic particles PROPERTY PROTON NEUTRON ELECTRON Mass/kg 1.673 x 10 -27 1.675 x 10-27 0.911x 10-30 (very nearly 0) Charge/C (Coulombs) +1.602x10-19 0 -1.602 x10-19 Position In the nucleus In the nucleus Around the nucleus These numbers are extremely small. In practice we use relative masses and charges. Relative atomic mass, Ar The relative atomic mass of an element is the average mass of the naturally occurring isotopes of the element relative to the mass of an atom of 12C (one atom of carbon 12 is given a relative atomic mass of exactly 12) ATOMIC NUMBER, Z=NUMBER OF PROTONS=NUMBER OF ELECTRONS Relative Isotopic mass The relative isotopic mass is the mass of an isotope of an element relative to the mass of an atom of carbon 12 (one atom of carbon 12 is given a relative atomic mass of exactly 12) Relative Molecular Mass, Mr The relative molecular mass of a compound is the mass of a molecule of the compound relative to the mass of an atom of carbon 12 (one atom of carbon 12 is given a relative atomic mass of exactly 12) ...read more.

Middle

There are 4 key stages, which are: > Ionisation > Acceleration > Deflection > Detection 1. the sample is investigated in the gasesous state. If the sample is a gas or a volatile(unstable) liquid, it is injected into the instrument directly. If the sample is a solid it is vaporise first by heating and then passes into the ionisation chamber. 2. Ionisation-(need to have gaseous ions)a beam of high-energy-electrons from an electron gun knocks out electrons from molecules or atoms of the sample so that they form positive ions. Nearly all the molecules/atoms lose just 1 electron and form ions with a 1+ ion. 3. acceleation(need the ions to be moving at the same speed) these positive ions are attracted towards negatively charged plates which accelerate them to a high speed (the instrument is kept under a high vacuum so that these ions do not collide with air miolecules, which might stop them from reaching the detector) 4. some ions pass through a pair of slits in these plates, forming the ions into a beam. The speed they reach depends on their mass- the lighter the ions the faster they go. 5. deflection(need the ions to be separated into separate isotopes) the beam then moves into a magnetic field at right angles to its direction of travel. The magnetic field bends the beam of ions into an arc of a circle. ...read more.

Conclusion

The arrangement of the sub-atomic particles > The protons and neutrons are in the centre of the atom held together by a force called the strong nuclear force. This is much stronger than the electrostatic forces that hold electrons and protons together in the atom, but it only acts over very short distances ie. Within the nucleus. > Electrons surround the nucleus. Electrons are found in a series of orbits or shells which get further and further away from the nucleus. The scale of the atom A typical atom has a nucleus that is about 1x10-15 m across, while the atom itself is about 1x10-10m across. This makes the nucleus about 10 000 times smaller than the atom itself. The shells of the electrons are relatively a huge distance from the nucleus and an atom is mostly empty space. The arrangement of the electrons The electron shells can hold different numbers of electrons. The first shell, which is closer to the nucleus, fills first, then the second and so on: > The first shell holds up to 2 electrons > Second-8 electrons > Third- 8 electrons with reserve space for 10 more. Electron diagrams If we known the atomic number of an atom, we know the number of electrons it has. We can therefore draw an electron diagram in the same style for any element. We can write electron diagrams in shorthand: > Write the number of electrons in each shell, starting with the inner shell and working outwards. Separate each number by a comma. For magnesium we would write 2,8,2 ...read more.

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The student has not specified the question that was set to them, but based on the piece of work, it may be presumed that it was about atomic structure. In relation to this, the student has given a detailed description ...

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Response to the question

The student has not specified the question that was set to them, but based on the piece of work, it may be presumed that it was about atomic structure. In relation to this, the student has given a detailed description of the atomic structure and has consequently answered the question well. The layout of the work is very clear (despite some rather large gaps between different sections in the work) which helps the examiner identify the relevant sections immediately. Clarity of a piece of work is key to high marks as the information is clear and easy to find so no doubts may be raised over a point the student has made in their work. This all works to the student’s advantage. However, I would strongly recommend using the superscript for ‘powers’ rather than simply making the font smaller.

Level of analysis

The student clearly shows an understanding of the topic and gives detailed and relevant examples to support this. This has worked to their advantage as it furthers the fact that they have understood the course. At times, the student develops the points made further by explaining why a process is necessary. This was particularly evident in their section explaining about the mass spectrometer. Further explanations made make the piece of work stand out from others and will score the student a higher mark. No evaluation or conclusion was required. The content in the work is good.

Quality of writing

There was an irregular usage of full stops are the end of bullet points. Whilst perhaps being slightly ‘picky’, even such little things may be picked up by examiners despite it, alone, not having a significant effect on the final mark. One problem with this piece of work was the failure of capitalising letters where necessary, but more surprisingly, the failure to have acknowledged words being misspelt! Especially when word processing programs pick up on such words, it is unacceptable for the words to remain misspelt.
The appropriate technical terms were used where necessary. This was expected of the student and they have applied it accordingly to their work with the appropriate definitions given for clarity.
The student presents the written work at a level that is expected of them. Bullet points are a conventional way of presenting the information at GCSE level and the student has used them well in laying out their work.


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