The Greek Philosophers were the first people to propose that all matter was composed of tiny particles

They proposed all matter was composed of tiny indivisible pieces

an Element is a substance that cannot be split up into simpler substances by chemical means

Humphrey David discovered the elements potassium, sodium, barium, strontium and magnesium

Johann Dobreiner arranged elements in groups called triads. A triad is a group of 3 Elements with similar chemical properties in which the atomic weight of the middle element is approximately equal to the average of the other two.

John Newland arranged elements in order of increasing atomic weight in groups called octaves. The first and eighth elements had similar properties. They didn’t always work as many elements weren’t discovered at the time.

Newlands Octaves are groups of elements arranged in order of increasing atomic weight in which the first and the eighth element of each group had similar properties.

Dmitri Mendeleev

• Mendeleev arranged elements in order of increasing atomic weight

• Mendeleev’s Periodic Law; When elements are ordered by increasing atomic weight ( Relative atomic Mass) the properties of the elements vary periodically

• He placed elements with similar properties in vertical columns called groups.

• He left gaps in his table to make elements fit into the proper columns. These gaps were for undiscovered Elements

• In a few cases, he had to reverse the order of elements to make them fall into groups of elements with similar properties. (i.e Te + I )

Henry Mosely used XRays to determine the atomic number of elements. By arranging the elements in order of increasing atomic number there was no need to reverse the order as Mendeleev did.

The modern periodic table is an arrangement of all known elements in order of increasing atomic numbers

• Determining the atomic number of an element

• Determining the mass number of an element

• Determining the chemical symbol of an element

• Grouping together the elements with similar physical and chemical properties

• Try to demonstrate trends in the physical and chemical properties of elements

• Distinguishing between metals and non-metals

Relative Atomic Mass is defined as

• The average of the mass numbers of the isotopes of the element

• As they occur naturally

• Taking their abundance into account

• Expressed on a scale in which the atoms of the carbon 12 isotope will have a mass of exactly 12 units

Group 1 Alkali Metals

H, Li, Na, K,Rb , Cs ,Fr

• Stored under oil to prevent them from reacting with oxygen and water

• Soft Shiny Highly reactive metals

• Reactivity increases down the group

• One electron on the outer shell

• They react with oxygen to form oxides

• They react with water to form hydroxides

Group 2 Alkaline Earth Metals

Be, Mg, Ca, Sr, Ba, Ra

• Harder metals than Alkali metals

• Reactivity increases down the group

• 2 electrons on the outer shell

Readily form divalent cathons

Group 7 The Halogens

F, Cl, B, I, At

• Fluorine + Chlorine are gases, Bromine is a liquid, and Iodine and Astatine are gases

• 7 electrons on the outer shell

• Very reactive

• Reactivity decreases down the group

• Oxidising agents

Group 8 Noble Gases

He, Ne, Ar, Kr, Xe, Rn

• Very unreactive

• Full outer shell

• Do not form compounds

• Boiling points increase down the group

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