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Chemistry Form 4: Chapter 4 - Periodic Table

  Elements in the periodic table are arranged in periods (row) and groups(column). 

  Groups include having the same electron arrangement in their outermost

shell, which results in group elements sharing similar chemical properties.   The electrons in the outermost shell is termed valence electrons.   Valence electrons determine the chemical properties of the element and

participate in chemical bonding. 

Chemistry Form 4: Chapter 4 - Dmitri Mendeleev ( Father of Periodic

Table)

Dmitri Mendeleev was born at Tobolsk, Siberia in 1834 and died in 1907. Mendeleev studiedscience at St. Petersburg and graduated in 1856. In 1863 Mendeleev was appointed to aprofessorship and in 1866 he succeeded to the Chair in the University.

Mendeleev is best known for his work on the periodic table; arranging the 63 known elements intoa Periodic Table based on atomic mass, which he published in Princ ip les of Chemistry  in 1869.

His first Periodic Table was compiled on the basis of arranging the elements in ascendingorder of atomic weight and grouping them by similarity of properties. 

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 Mendeleev provided for variance from strict atomic weight order, left space for new elements,and predicted three yet-to-be-discovered elements including eke-silicon and eke-boron. Histable did not include any of the Noble Gases, however, which had not yet been discovered.  

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The original table has been modified and corrected several times, notably by Moseley, but it hadaccommodated the discovery of isotopes, rare gases, etc.  

Chemistry Form 4: Chapter 4 - Physical Properties of Group 1 Elements

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  Group 1 elements are soft metal and can be cut with a knife 

  Silvery grey surface

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  Low density compared to other metals 

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  Lower melting and boiling points than most other metals 

As the atomic radius increases, the charges are further apart and the electrical attractive force is

reduced. This results a weaker metallic bond and little heat energy is needed to overcome the bond. Thus, the melting/boiling point decreases as we go down the group. 

Chemistry Form 4: Chapter 4 - Reactivity of Group 1

Reactivity of Group 1 increases when go down the group. 

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 WHY? 

  When an alkali metal atom reacts, it loses an electron to form a singlypositively charged ion which is a stable noble gases electron arrangement.  

  When go down the group, the atomic radius gets bigger due to an extrafilled electron shell and the outer electron is further and further away fromthe nucleus. 

  Therefore the outer electron is less strongly held by the positive nucleusas the attractive force is decreased.

   As a result, the outer electron is more easily lost and react more

vigorously. 

Chemistry Form 4: Chapter 4 - Physical Properties of Halogen

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  The melting and boiling points increases down the group as the atomic radius

increase.

  The van der Waals become stronger and thus more heat energy is needed to

overcome these forces between the molecules.

  The physical state of halogens change gradually from gas to liquid to solid due toan increase in melting and boiling point.

Chemistry Form 4: Chapter 4 - Reactivity of Group 17

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  When a halogen atom reacts, it gains an electron to form a singly charged

negative ion which has a stable noble gas electron arrangement.

  As you go down the group of 17, the atomic radius gets bigger due to an extra

filled electron shell.

  The valence electron is further and further away from the nucleus.

  The forces of attraction between the nucleus and the valence electrons becomeweaker, making it more difficult to gain electrons.

  Therefore, the halogen is less reactive down the group.

Chemistry Form 4: Chapter 4 - Special Characteristics of Transition

Elements

1. Transition elements can form coloured compounds 

2. Transition elements have varying oxidation number 

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  Iron has two common oxidation states (+2 and +3) in, for example, Fe 2+ and Fe3+. It also has a less common +6 oxidation state in the ferrate(VI)ion, FeO4

2-.   Manganese has a very wide range of oxidation states in its compounds.

For example:

+2  in Mn2+ 

+3  in Mn2O3 

+4  in MnO2 

+6  in MnO4- 

+7  in MnO4

-

 

3. Transition elements can form complex ions 

  A complex ion has a metal ion at its centre with a number of othermolecules or ions surrounding it.

  Some examples of complex ions formed by transition metals

[Fe(H2O)6]2+, [Co(NH3)6]

2+, [Cr(OH)6]3- , [CuCl4]

2- 

4. Transition elements can act as catalysts 

  Iron in the Haber Process  The Haber Process combines hydrogen and nitrogen to make ammoniausing an iron catalyst. 

  Vanadium(V) oxide in the Contact Proc ess  

At the heart of the Contact Process is a reaction which converts sulphur

dioxide into sulphur trioxide. Sulphur dioxide gas is passed together withair (as a source of oxygen) over a solid vanadium(V) oxide catalyst. 

  Nickel in the hyd rogenat ion of C=C bonds  This reaction is at the heart of the manufacture of margarine from

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vegetable oils. However, the simplest example is the reaction between ethene andhydrogen in the presence of a nickel catalyst.