the early periodic table
- Scientists didn't know about atomic structure so they based the first table on atomic weight.
- In 1863 Newland proposed a law of octaves, which stated that similar properties are repeated every eighth element.
- He put the 62 elements known at that time into seven groups according to atomic weight.
- After calcium their properties didn't match as well within the groups
- This meant other scientists rejected this theory
- In 1869 Mendeleev produced a better table, where he left gaps for undiscovered elements
- He then tried to predict the properties of undiscovered elements and was right
- After this many scientist accepted his idea.
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the modern periodic table
- Scientist found out about protons and electrons at the start of the 20th century.
- Soon after they developed models of the arrangements of electrons in atoms.
- The atomic number of an element determines its position in the periodic table.
- The number of electrons in the outer shell determines the properties
- The group number equals the number of electrons on the outer shell
- As the atom gets larger the less strongly attached to the nucleus
- when metals react they lose electrons, so the reactivity of the metals in a group increases going down a group
- when non metals react the gain electrons,so the reactivity of non-metals decreases down a group.
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group 1- alkali metals
- these metals react with air and water
- they are soft solids at room temperature
- they have a low melting point and a boiling point that decreases down the group
- the have low densities
- they react with water to produce hydrogen gas and a metal hydroxide that is an alkali
- they all have one electron in the outer shell they lose this electron in reactions to form an ionic compound in which they become positive -the react with halogens (group 7)
- they dissolve in water forming solutions that are colourless
- the reactivity increases as you go down
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- the transition elements are found in the period table between group 2 and 3
- except for mercury,they have a higher melting and than the alkali metals
- they are malleable and ductile and they are good conductor of heat and electricity
- they react only slowly or not at all, with oxygen and water.
- they form positive ions
- they can be used as industrial catalyst
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- the halogens are non-metallic in group 7 of the periodic table
- they exist as small molecules made up of pair of atoms. they have low melting and boling points that increases godown the group. fluorine is a pale yellow gas
- cholorine is green gas
- bromine is a red-brown liquid
- iodine is a grey solid
- all of the halogens have seven electrons in their outer shell
- the reactivity of halogens decreases going down the group
- a more reactivite halogenan displace a less reactive halogen from a solution of one of its salts.
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