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To understand the characteristics of the elements that are in different groups in the periodic table.
Group I - the alkali metals
Group I - the alkali metals
The ALKALI METALS are the most reactive metals that occur. They are know as the alkali metals because they react vigorously with water to produced hydrogen and an alkali solution.
COMMON PROPERTIES:
They are soft solids
Low melting point and density
Highly reactive --> they are stored under oil to prevent them react with oxygen and water vapor
Have a light- grey, silver surface
Reactivity increase down the group
Physical properties change as we go down the group
The melting point becomes lower down the group
Density increases down the group
All react with water to form hydroxide and an alkali solution of the metal hydroxide.
Group VII - the halogens
Group VII - the halogens
They are the most reactive non-metals
Reactivity decrease down the group
Melting and boiling point increase down the group
The lowest element is radioactive
The intensity of colour increase down the gropu (from pale to dark)
COMMON PROPERTIES:
They all are non-metals
They are all poisonous and have a similar strong smell
They all form diatomic molecules (ex. Cl2, Br2, I2)
They all have a valency of 1 and form compound with similar formulae (ex. HCl, HBr, HI)
Their compounds with hydrogen are usually strong acids when dissolved in water.
They each produce a series of compounds with other elements: chlorides, bromides and iodides. Together these are known as HALIDES
The halogens themselves can react directly with metals to form metal halides or SALTS
They all form negative ions carrying a single charge (ex. (Cl-), (Br-), (I-))
CHLORINE:
dense pale-green gas
smelly and poisonous
occurs as chlorides, especially sodium chloride in the sea
BROMINE:
deep-red liquid with red-brown vapour
smelly and poisonous
occurs as bromides, especially magnesium bromide in the sea
IODINE:
grey solid with purple vapour
smelly and poisonous+occurs as iodides and iodates in some rocks and in seaweed
The chemical reactivity of the halogens
The chemical reactivity of the halogens
Fluorine and chlorine are very reactive.
ex: Chlorine dissolves in water to give an acidic solution. This mixture is called CHLORINE WATER and it reacts as:
an oxidating agent.
a bleah --> some coloured substances lose their colour when they are oxidized.
Cl2 + H2O --> HCl + HClO
This reaction is used as the chemical test for chlorine gas.
Damp litmus or the Universal Indicator paper is bleached when held in the gas.
The DISPLACEMENT REACTION demonstrates the order of reactivity.
ex: Cl2 + 2KBr --> 2KCl + Br2 // Chlorine displace bromide because it's more reactive.
Cl2 + 2KI --> 2KCl + I2 // Chlorine displace iodine because it's more reactive.
Br2 + 2KI --> 2KBr + I2 // Bromide displace iodine because it's more reactive.
Group VIII/ 0 - The noble gas
Group VIII/ 0 - The noble gas
The electron arrangements of the atoms of the noble gas are very stable. This means that they do not react readily with other atoms. In fact, in many situations where atoms of other elements bond or react chemically, they are trying to achieve that stable arrangement of electrons found in the noble gas.
COMMON PROPERTIES:
All of the are present in the Earth's atmosphere (make up 1%)
They all are very unreactive (inert gas)
They do not combine with each other
Have a melting and boiling point extremely low (Helium has the lowest melting point of any elements)
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