C3

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  • Created on: 17-04-11 14:08
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C3
Development of the periodic table:
The early periodic table:
The periodic table of elements developed as an attempt to classify the
elements. It arranges them in a pattern according to their properties.
Early versions of the periodic table failed to take account of the fact that
not all the other elements were known at that time.
Mendeleev's table took account of unknown elements, and so provided
the basis for the modern periodic table.
The modern periodic table:
The group that an element is in is determined by its atomic/proton
number.
The number of electrons in the highest energy level of an atom
determines its chemical properties.
We can explain trends in reactivity as we go down a group in terms of
the number of energy levels in the atoms.
Group 1 ­ the alkali metals:
The elements in Group 1 of the periodic table are called the alkali
metals.
The metals all react with water to produce hydrogen and an alkaline
solution containing the metal hydroxide.
The reactivity of the alkali metals increases as we go down the group.
Group 7 ­ the halogens:
The halogens exist as diatomic molecules
The halogens all form ions with a single negative charge.
The halogens form covalent compounds by sharing electrons with other
non-metals.
The reactivity of the halogens decreases going down the group
The transition elements:
Nearly all the transition elements have high melting points and high
densities.
The transition metals are strong and hard, and are good conductors of
electricity and heat.
The transition metals do not react vigorously with oxygen or water.

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More about acids and bases:
Strong and weak acids/alkalis:
Acids in aqueous solutions produce H+ ions.
Alkalis in aqueous solutions produce OH- ions.
A strong acid or base in 100% ionised in water
A weak acid or alkali is only partially ionised in water.…read more

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Water
Water and solubility:
Water evaporates from rivers, lakes and oceans and condenses to form
clouds, returning to the surface as rain.
Most ionic substances are soluble in water, but many covalent
compounds are not.
A saturated solution contains the maximum amount of solute that will
dissolve at that temperature.
Solubility curves:
The solubility of most solid solutes increases with temperature.…read more

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Energy calculations:
Comparing the energy produced by fuels:
When fuels and food react with oxygen, energy is released ­ this
reaction is exothermic.
A simple calorimeter can be used to compare the energy released by
different foods in a school chemistry lab
Energy changes in reactions:
In chemical reactions, energy must be supplied to break the bonds
between atoms in the reactants.
When bonds are formed between atoms in a chemical reaction, energy
is released.…read more

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Analysis:
Test for positive ions:
Group 1 and 2 metals can be identified in their compounds using flame
tests.
Sodium hydroxide solutions can be used to identify different metal ions,
depending on the precipitate that is formed
Ammonium ions produce ammonia when sodium hydroxide is added,
and the solution is (gently) heated.
Tests for negative ions:
We identify carbonates by adding dilute acid, which produces carbon
dioxide gas.…read more

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