OCR Chemistry C4

Notes about C4 in GCSE Chemistry. (Not complete topic).

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  • Created on: 31-05-16 17:39
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Chemistry C4 Book Notes
The structure of an atom
Electrons () mass is nearly nothing
Protons (+) mass is 1
Neutron (no charge) mass is 1
Mass and atomic number
Mass Number (number of protons and neutrons)
Proton number
In the periodic table the elements are ordered by their proton number. The number of protons is
equal to the number of electrons.
1st shell ­ 2 electrons
2 shell ­ 8 electrons
3rd shell 8 electrons
4th shell ­ remainder 1
The development of the periodic table
Johan Döbereiner noticed that some elements could be grouped together because they had the
same physical or chemical properties. He tried to organise the elements into triads where the
middle element of each triad had a relative atomic mass that was the average of the other two.
This did not work.
John Newlands investigated the properties of known elements. He built his ideas of the work of
earlier scientists and he built a table of elements, which were ordered by increasing atomic weight.
He detected a pattern where elements with similar properties appeared in the same columns. He
noticed that every eighth element had similar properties. These sets of eights were called
Newland's octaves. However, this idea did not work.
Dmitri Mendeleev tried to spot patterns with elements and their chemical properties. He had an
insightful dream and laid out the cards of the elements. He put them in order of atomic mass, like
Newlands did, but he left gaps to keep elements with similar properties in the same vertical
groups. The gaps were for undiscovered elements.
The quality or character of being periodic the tendency to recur at intervals.
Group 7 (Halogens)
They have 7 electrons in outer shell.
Reactivity decreases as you go down the group.
This is because the electrons are further away from the nucleus
so extra electrons aren't attracted as much.

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The ions formed are held with enormously strong forces of attraction between the oppositely
charged ions. This electrostatic force of attraction, which acts in all directions, is called an Ionic
An ion is a charged atom or molecule. It is charged because the number of electrons does not
equal the number of protons in the atom.
The ionic bonds between the charged particles results in an arrangement of ions we call a giant
structure.…read more

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As you move down the periods an extra shell is added.
Elements in the same group have the same number of electrons in their outer shell.
Properties of Group 1 and Group 7 Ionic Compounds
They have high melting points due to the high number of ionic bonds that need to be broken down.
They are crystalline solids and they are colourless solids.
When they are solid they do not conduct electricity, but if they are melted or dissolved in water,
they conduct electricity.…read more

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Line spectra
Each spectrum consists of a series of lines. You can view a spectrum through a
spectroscope. A spectroscope is where light enter through one telescope, at an
angle, and is then split into a spectrum by a glass prism. This is viewed with a
second telescope, also at an angle.
Bunsen and Kirchhoff built a spectroscope. They used the light from a flame to split
into a spectrum.…read more


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