Chemistry C4, C5, C6 OCR 21st Century

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Preview of Chemistry C4, C5, C6 OCR 21st Century

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C4 ­ Chemical patterns
C4.1 What are the patterns in the properties of elements
Elements are the `building blocks' of all materials ­ the atoms of each element have a different
proton number. The elements are arranged in order of ascending atomic (or proton) number, this is
the number of positive protons in each atom.
Putting elements in this order gives a repeating pattern of their properties.
Knowledge of chemical facts began to grow in the 18th and 19th centuries ­ as a result scientists
tried to find patterns in order to stop themselves being overwhelmed by the mass of information
and to provide a basis for understanding the facts. Many of the early attempts of classification were
dismissed by the scientific community as more information emerged.
Three of the most significant developments were made by Döbereiner, Newlands and Mendeleev.
Döbereiner (1829) Newlands (1864) Mendeleev (1869)
Döbereiner arranged elements Newlands only knew of the He put the known elements
in groups of three existence of 63 elements ; in order of relative atomic
The elements in each triad had may were still undiscovered mass
similar chemical properties and He arranged the known Mendeleev realised that
the relative atomic mass of the elements in order of relative some elements had yet to be
middle element was close to the atomic mass and found similar discovered, so he left gaps to
average of the other two properties amongst every accommodate their eventual
elements eighth element in the series discovery
For example: This makes sense since the He also predicted what the
Li ­ 7 Na ­ 23 K ­ 39 noble gases (Group 0) weren't properties of these
discovered until 1894 undiscovered elements might
be
Doesn't work for all elements Didn't work for all elements He used his periodic table
IGNORED Not all elements were to predict the existence of
discovered ­ caused problems other elements
REJECTED SUCCESSFUL

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During, the period of the 18th century actual masses could not be measured so they were compared
against the mass of hydrogen (the lightest) ­ this is called relative atomic mass. It is now measured
1 the mass of a carbon atom.
relative to 12
The periodic table gives us a great deal of information about each of the elements.…read more

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Because there are patterns in the way the elements are arranged in the periodic table, it can be used
to predict their properties and interpret data
Group 1 ­ Alkali metals
There are six metals in Group 1
As we go down the group, the alkali
metals become more reactive.
The alkali metals have low melting
and boiling points compared to most
other metals.…read more

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Some chemicals can harm us if they are not handled carefully ­ hazard symbols are used to identify
the danger posed by each chemical and what care should be taken
Hazard Symbol Meaning
These substances attack living tissues, including eyes and skin
and can damage materials
Corrosive
These substances can kill when swallowed, breathed in or
absorbed through skin
Toxic
These substances are similar to toxic substances, but they are
less dangerous
Harmful
These substances provide oxygen, which allows other
substances to burn more fiercely…read more

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The following hazard symbols are found on alkali metals and their compounds:
Chemical Hazard symbol
Lithium
Lithium chloride
Sodium
Sodium
hydroxide
Potassium
Therefore when working with Group 1 metals, the following precautions should be taken:
Use small amounts of very dilute concentrations
Wear safety glasses and use safety screens
Avoid working near naked flames
Group 7 ­ The halogens…read more

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There are five non-metals in group 7
The halogens have low melting points
and boiling points ­ this is a typical
property of non-metals. Fluorine has the
lowest melting point and boiling point ­
the melting points and boiling points
then increase as you go down the group.
The halogens become less reactive as
you go down the group ­ Fluorine at the
top of the group is the most reactive
halogen.…read more

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Chlorine,
Cl
Bromine, Br
Iodine, I
Therefore working with halogens, the following precautions should be taken:
Wear safety goggles
Work in a fume cupboard
Make sure the room is well ventilated
Use small amounts of very dilute concentrations
Avoid working near naked flames
Need to know
Hydrogen, H2
Water, H2O
Chlorine, Cl2
Bromine, Br2
Iodine, I2
Halide ­ a binary (dual) compound of a halogen with another element or group
Each of the group 1 halides has a formula with one symbol for the metal…read more

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An atom has the same number of protons (positive) as electrons (negative), so the atom as a
whole is neutral (i.e.…read more

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The electron configuration is written as a series of numbers, e.g., oxygen is 2.6; aluminium is
2.8.3 and potassium is 2.8.8.1
The chemical properties of an element are determined by its electron arrangement
C4.3 How do chemists explain the properties of compounds of Group 1 and Group 7 elements
Chemists use their observations to develop theories to explain the properties of different
compounds.
For example, experiments show that molten compounds of metals and non-metals such as lithium
chloride, conduct electricity.…read more

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Most non-metal elements are molecular and most of these consist of molecules with just two atoms
joined together. Most compounds, between non-metal elements are also molecular.
Intermolecular forces ­ all of these substances have very strong covalent bonds between the
atoms, but much weaker forces holding the molecules together. When one of these substance melts
or boils it is these weak `intermolecular forces' that break, not the strong covalent bonds.…read more

Comments

Ashvarya

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Dave

Can you please post C1 C2 C3 Notes as well as that we be helpful your are very good at making clear and easy to read notes 

Shakeebah

the download always fails???

mariyyah

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eminkinza

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