Placing Elements in Order

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Placing Elements in Order

Scientists have managed to place all the elements in order using the following system:

They are placed in order of increasing proton number.

Hydrogen is first with a proton number of 1.

Next the list of elements are picked out and placed into groups. Groups are defined by the number of electrons in the outer shell of the atom.

Example: Lithium has one electron in its outer shell so is placed into Group 1. Atoms with two outer shell electrons are placed in Group 2. There are eight groups in total.

Finally, the groups are placed next to one another to finally complete the Periodic Table:

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The groups

As has already been stated there are eight groups in the Periodic Table plus, a block of elements called the Transition Metals.

Some of the groups have special names:

Group 1: the alkali metals.

Group 2: the alkaline earth metals.

Group 7: the halogens.

Group 0 or 8: the noble gases.

The zigzag line through the Periodic Table separates the Metals on the left with the non-metals to the right of the line.

The Periods

The horizontal rows are called Periods.

Period 3 contains Sodium(Na), Magnesium(Mg), Aluminium(Al), Silicon(Si), Phosphorus(P), Sulphur(S), Chlorine(Cl) and Argon(Ar).

The Periods represent the energy shell these atoms outer electrons are located within.

Period 3 elements all have their outer electrons in the third energy level/shell.

Period 2 elements have their outer electrons in the second energy shell, and so on.

These atoms have more complicated electronic configurations. They are found in the long block in the middle of the periodic table:

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Often used in industry as catalysts.

Useful in making alloys.

They form coloured compounds.

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