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
In1869 Mendeleevproduced 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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transition element
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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halogens
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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