OCR B (Salters) Unit 2 Elements From The Sea

Notes made mainly using Chemical Ideas; have used the specification (included) to take relevant notes. Some bits are missing, either because I didn't want to revise them or they were too complex to type.

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Preview of OCR B (Salters) Unit 2 Elements From The Sea

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Chemistry Of Natural Resources-Elements From The Sea
Formulae, equations and amount of substance
Use the concept of amount of substance to perform calculations involving: molecular formulae,
percentage yield, masses of reagants, volumes of gases and concentrations of solutions; write and
interpret any balanced chemical equations required, including ionic equations*
A mole is 6.02x10^23 particles-known as Avogadro's constant. We compare the masses of
atoms with each other using carbon as standard. An elements' relative atomic mass is the average
mass of one atom of an element for a twelfth of the mass of one atom of carbon-12.
The reactions of an ionic substance often involve only one of the two types of ion. Because
the other two ions are on both sides of the equation, they are known as spectator ions and removed
from the equation. This new equation is now an ionic equation-it shows only the ions that take part in
the reaction.
Recall and explain the procedure for carrying out an acid-alkali solution, and be able to work out the
Atomic structure
Use conventions for representing the distribution of electrons in atomic orbitals
It is more appropriate to talk about certain electron shells, as opposed to energy levels, in
chemistry. The shells are labelled by giving each a principle quantum number, n; the higher the value
of n, the further the shell is from the nucleus, and the higher the energy associated with the shell.
Each shell has a limit to the number of electrons it can hold-a shell which contains its maximum number
of electrons is called a filled shell; electrons are arranged so that the lowest energy levels are filled
Chemists can explain many of the properties of atoms without needing to use a detailed
theory of atomic structure. Much chemistry is decided only by the outer shell electrons, and one very
useful model treats the atom as being composed of a core of the nucleus plus the inner electron
shells, surrounded by an outer shell (note: electron dot-cross diagrams)
Work out the electronic configuration of atoms from hydrogen to krypton, and the outer sub-shell
structures of other main group elements, in terms of main energy levels and s-, p- and d-atomic
orbitals and the elements' positions in the Periodic Table
When we come to look at elements other than hydrogen, we find their spectra are much
more complex-electron shells are not the whole story. The shells themselves are split up into
sub-shells. These are labelled s, p, d and f. The n=1 shell only has an s sub-shell; the n=2 shell has two
sub-shells, s and p; the n=3 shell has sub-shells s, p and d; and the n=4 shell has four sub-shells, s, p, d
and f.

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The sub-shells are themselves divided further into atomic orbitals: an s sub-shell always
contains one s atomic orbital; a p sub-shell always contains three p atomic orbitals; a d sub-shell
always contains five d atomic orbitals; an f sub-shell always contains seven f atomic orbitals.
The energy level of the 3d sub-shell lies just above that of the 4s sub-shell, but just below
the 4p sub-shell.…read more

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Metallic lattice-High melting point, insoluble in water, good conductor of electricity
Explain the term electronegativity; recall qualitatively the electronegativity trends in the Periodic
Table; use relative electronegativity values to predict bond polarity in a covalent bond; decide
where a molecule is polar or non-polar from its shape and the polarity of its bonds
Electronegativity is the ability of an atom to attract a covalently bonded electron pair-it's
`pulling' power.…read more

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Atoms in elements are in oxidation state zero; in simple ions, the oxidation state is the same
as the charge on the ion. Since compounds have no overall charge, the oxidation states of all the
constituent elements must add up to zero.…read more

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The group of an element refers to the number of outer shell electrons in an atom of
said element, which dictates how many electrons it will lose/gan when forming an
ion, and thus determining its charge
Recall the names and formulae of NO, SO², CO², OH, NH, HCO; write formulae for
compounds formed between these ions and other given anions and cations
Recall the meaning of the term ionisation enthalpy; write equations for the successive ionisations of
an element and explain periodic and group trends…read more

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With more electrons in each molecule, the strength of the intermolecular bonds increases, accounting
for the change in physical state of the halogens.
Use given information to compare different methods of manufacturing chemicals industrially, in terms
of atom economy, percentage yield, batch versus continuous process, siting the plant, cost of
process and raw materials, waste disposal, safety
In a batch process, the starting materials are put into a vessel and allowed to react together.…read more

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Bromine has a dense and choking vapour-the liquid produces painful sores if spilled on the
skin. Great care has to be taken when transporting bromine; most of it is carried in lead-lined steel
tanks, supported in strong metal frames-each tank holds several tonnes of the element. International
regulations control the design and construction of road and rail tanks.
Recall and describe some uses of halogen compounds which must be weighted against these risks
About 50 million tonnes of chlorine are produced worldwide annually.…read more

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See above
Organic reactions
Describe in outline the preparation of a chloroalkane from an alcohol using HCl
Reacting an alcohol with the appropriate hydrogen halide can make a monosubstituted
halogenoalkane. For example, chloromethane can be made by reacting methanol with hydrogen
chloride. This reaction is an example of a substitution reaction. Most of the chloromethane
manufactured industrially is made by this method.…read more

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Substitution reactions are typical of halogenoalkanes-for example, a substitution
reaction takes place between a halogenoalkane and hydroxide ions, in which the
halogenoalkane is hydrolysed to form an alcohol. For example, in bromobutane
(CH-CH-CH-CH-BR), the C-Br bond is polar, and the oxygen atom of the hydroxide
ion is negatively charged. The partial positive charge on the carbon atom attracts the
negatively charged oxygen of the hydroxide ion.…read more

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The great strength of the C-F bond makes it very difficult to break, so fluoro compounds are
very unreactive. As you go down the group, the C-Hal bond gets weaker, so the compound becomes
more reactive. Bromo and iodo compounds are fairly reactive, which makes them useful as
intermediates in synthesising other organic compounds.
You might imagine that a large bond polarity in a C-X bond would result in it breaking easily.…read more


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