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Topic 1.4

PERIODICITY

The Periodic Table
Trends in Period 3
























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THE PERIODIC TABLE

The periodic table is a list of all known elements arranged in order of increasing atomic
number, from 1 to 106. In addition to this, the elements are arranged in such a way that
atom with the same number of shells is placed together, and atoms with…

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He is placed in group 0 on this basis, but hydrogen does not behave like any other
element and so is placed in a group of its own. Hydrogen is sometimes placed above
group 1 or group 7 that is why it has a +1 charge and -1 charge. However,…

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All elements belong to one of four main blocks: the s-block, the p-block, the d-block and
the f-block.

The s-block elements are all those with only s electrons in the outer shell.

The p-block elements are all those with at least one p-electron in the
outer shell.

The d-block elements…

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Elements coloured black are in the f-block

The physical and chemical properties of elements in the Periodic Table show clear
patterns related to the position of each element in the Periodic Table. Elements
in the same group show similar properties, and properties change gradually on
crossing a Period.
All these…

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TRENDS IN PERIOD 3

1. Properties of individual atoms

a) Atomic radii
Atomic radii is the half the distance between the centre of a pair of atoms.
It tells us about the size of atoms. We cannot measure the radius of an isolated
atom because there is no clear point…

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b) Ionization energies

Ionization energy generally increases across period 3 but decreases between
groups II and III and also between groups V and VI.
Ionization energy increases across period 3 because the nuclear charge
increases but the shielding remains the same, making the electrons harder to
remove. I
Ionization energy…

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2. Structure and Bonding

The structure and bonding of the elements in period 3 of the Periodic Table varies widely.
There is a gradual decrease in metallic character in crossing a period.

On crossing a period the ionisation energies increase so it becomes more
difficult to remove electrons and form…

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The trends in intramolecular bond type can be seen in the following table:

Na Mg Al Si P S Cl Ar
metallic metallic metallic covalent covalent covalent covalent -


The variation on bond type causes a number of differences in the structures of the
Period 3 elements which in turn…

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b) Silicon

Silicon is a giant covalent macromolecule. Silicon atoms form infinite lattices
in which all the atoms are held together by strong covalent bonds. Since the
structure cannot be broken up without breaking these strong covalent bonds, it
follows that silicon has a very high melting and boiling point.…

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