The Sub-atomic particles

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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

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) (the molecular mass is found by adding together the relative atomic masses of all the atoms of the molecule)

MASS NUMBER, A=NUMBER OF PROTONS+NEUTRONS

NUMBER OF NEUTRONS=MASS NUMBER-ATOMIC NUMBER

Relative Formula Mass, Mr

The relative formula mass is the relative mass of one formula unit of an ionic 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).

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Ions

These are atoms which have lost or gained electrons, and are no longer neutral. The number of electrons is no longer the same as the number of protons.

e.g. a lithium atom loses an electron to form a positive lithium. A lithium ion has the following number of sub-atomic particles:

Protons=3

Electrons=2

Number of neutrons= 7-3=4

ISOTOPES AND THE CARBON-12 SCALE OF ATOMIC MASS

ISOTOPES-atoms with the same number of protons but different numbers of neutrons.

  • It is the number of protons, the atomic number z, which defines the ...

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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.

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.

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.