notes on entire chemistry unit 3, higher tier

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Chemistry C3
Development of the Periodic Table
The Early Periodic Table
Early periodic table based on atomic masses
Newlands law of octaves was the properties of elements repeated every eighth element
This failed because:
o He didn't allow for undiscovered elements
o Properties of the elements didn't match very well
Arranged elements in order of atomic mass but swapped some elements around so that they
follow a pattern
Left gaps for undiscovered elements
Also predicted their properties & when they were discovered, they were very accurate
Ideas were accepted
Modern table based on his ideas
The Modern Periodic Table
Elements arranged in order of atomic (proton) number
Elements with similar properties are in the same group
Atoms in same group have same number of electrons in their outer energy level (shell)
Group 1
Reactivity increases down the group
This is because atoms get bigger down the group so the single electron in the outer shell is less
strongly attracted to the positive nucleus of the atom
This is because the inner energy levels screen the outer electron from the nucleus
This is called shielding
Because of shielding, the outer electron is easier to lose and so the reactivity increases as the
size increases.
Group 7
Reactivity decreases down the group
As atoms get bigger, the electron which needs to be added to the outer shell is less strongly
attracted to the positive nucleus
This is because the inner energy levels shield the electrons on the outer shell form the positive
Therefore reactivity decreases down the group

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The Transition Elements
All metals with typical metal properties:
Good conductors
Strong & Dense
Higher melting and boiling points than metals in groups 1 & 2 (except mercury)
Used as building materials
Only react slowly with water and air
Often coloured
Can act as catalysts
Form positive ions with various charges
Summary Development of the Periodic Table
In the 19th century scientists tried to classify elements. They arranged them in order of atomic
mass and produced the first periodic tables.…read more

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More about Acids and Bases
Strong & Weak Acids
Acids dissolve in water to form hydrogen ions which are also protons
Therefore acids are proton donors
In solution the protons are surrounded by water molecules and are hydrated, they are denoted
by H+ (aq)
A strong acid ionises fully in water
Weak acids only partly ionise in water
Strong acid solutions have a higher pH and react faster than a weak acid solution with the same
Alkalis are soluble bases and they produce OH…read more

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Strong acid + Strong alkali ­Any indicator
W eak acid + Strong alkali ­P henolthalein
Strong acid + W eak alkali ­Menthyl Orange
Weak acid + Weak alkali can't be titrated because there is no endpoint
Adding an acid to an alkali produces a neutralisation reaction. The point at which enough acid has been
added to completely react with the alkali is called the end point. This can be shown using a chemical
called an indicator.…read more

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Water & Solubility
The Water Cycle
Water in the rivers, lakes and oceans of the Earth evaporates as the Sun supplies it with energy
The water vapour formed rises into the atmosphere where it cools and condenses into tiny
water droplets that form clouds
As the clouds rise, they become cooler and the droplets get bigger and eventually fall as rain
This replenishes the water in the rivers, lakes and oceans
This is called the water cycle
What Dissolves?
Most gases and ionic compounds…read more

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Water evaporates from large masses of water on the earth's surface and forms vapour. As this rises water droplets
condense and eventually fall to the surface as rain. This circulation of water is called the water cycle. When as much
solute as possible is dissolved in a solution at a particular temperature, we say that the solution is saturated.…read more

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Hard water contains calcium and/or magnesium salts. These react with soap to form scum. The salts
also produce scale when the water is heated. This is a poor conductor of heat, and makes kettles and
water heaters less efficient. Hard water may be better for human health than soft water.…read more

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