Periodic table

• The periodic table


  The elements in the periodic table are arranged in order of atomic (proton) number and so that elements with similar properties are in columns, known as groups.

  The table is called a periodic table because similar properties occur at regular intervals.

  Elements in the same group in the periodic table have the same number of electrons in their outer shell (outer electrons) and this gives them similar chemical properties.
• Development of the periodic table

  Before the discovery of protons, neutrons and electrons, scientists attempted to classify the elements by arranging them in order of their atomic weights.

  The early periodic tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed.
• Development of the periodic table (2)

  Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights. Elements with properties predicted by Mendeleev were discovered and filled the gaps. Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always correct
• Metals and non metals

  Elements that react to form positive ions are metals. Elements that do not form positive ions are non-metals. The majority of elements are metals. Metals are found to the left and towards the bottom of the periodic table. Non-metals are found towards the right and top of the periodic table
• Metals

  When metals react they lose electrons to achieve a full outer energy level

  This gives them the stable electronic structure of Group 0 noble gases

  Metals always form positive ions
• Group 0

  The elements in Group 0 of the periodic table are called the noble gases.

  They are very unreactive and do not easily form molecules because their atoms have stable arrangements of electrons - full outer shell

  The noble gases have eight electrons in their outer shell, except for helium, which has only two electrons.

  The boiling points of the noble gases increase with increasing relative atomic mass (going down the group)
• Group 1

  The elements in Group 1 of the periodic table are known as the alkali metals and have characteristic properties because of the single electron in their outer shell.

  Students should be able to describe the reactions of the first three alkali metals with oxygen, chlorine and water.

  In Group 1, the reactivity of the elements increases going down the group.

  Very soft, react with oxygen in the air
• Group 1

  Lithium / sodium + water turns universal indicator purple, producing hydrogen gas, it is a vigorous reaction

  Potassium and water produce a lilac flame

  Sodium and water may produce a yellow flame
• Group 7

  The elements in Group 7 of the periodic table are known as the halogens and have similar reactions because they all have seven electrons in their outer shell.

  The halogens are non-metals and consist of molecules made of pairs of atoms. Students should be able to describe the nature of the compounds formed when chlorine, bromine and iodine react with metals and non-metals.

  In Group 7, the further down the group an element is the higher its relative molecular mass, melting point and boiling point.
• Group 7


  In Group 7, the reactivity of the elements decreases going down the group.

  A more reactive halogen can displace a less reactive halogen from an aqueous solution of its salt

  Halogens react with each other and covalent bond to make eachother stable

  All non metals

  They displace each other from solutions depending on reactivity
• Transition metals

  The transition elements are metals with similar properties which are different from those of the elements in Group 1.

  Students should be able to describe the difference compared with Group 1 in melting points, densities, strength, hardness and reactivity with oxygen, water and halogens.

  Students should be able to exemplify these general properties by reference to Cr, Mn, Fe, Co, Ni, Cu.
• Properties of transition metals


  Hard and strong metals

  High melting points other than mercury

  All have a high density

  Much less reactive than Group 1

  Can form ions with different charges

  Form coloured compounds

  Can be used as catalysts

  Many transition elements have ions with different charges, form coloured compounds and are useful as catalysts.

  Students should be able to exemplify these general properties by reference to compounds of Cr, Mn, Fe, Co, Ni, Cu