Chemistry Applications

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1st Diploma Applied Science

Unit 3 – Chemistry Applications

Assignment no. 1

  1. Know how atomic structure relates to the properties of the elements and compounds
  2. Understand the factors involved in chemical reactions.  

Task 1

1.a

  

Key:

p+ - proton

n0  - neutron

e-  - electron

The nucleus of every atom contains two types of particle – protons and neutrons. The number of protons gives the atomic number. Protons have a positive electronic charge, while neutrons have none. The electrons that spin around the nucleus, like planets orbiting the Sun, have a negative charge. But electrons are not ‘solid balls’, they are bundles of energy that move almost as fast as light. There are always the same numbers of electrons and protons in an atom.

number of  protons = atomic number of the atom

number of electrons = number of protons

number of protons + number of neutrons = mass number

number of neutrons = mass number – number of protons

Isotopes

All the atoms of an element have the same number of protons, but some have different numbers of neutrons. All of these are called isotopes, e.g.:

These different atoms are isotopes of carbon. The fact that they have varying numbers of neutrons makes no difference whatsoever to the chemical reactions of the carbon.

There are 3 kinds of oxygen atom 16O, 17O, 18O :

1. b & c

Group 1 Alkali Metals (Li, Na, K, Rb, Cs, Fr)

The Alkali Metals from group 1 of the periodic table, are called so because they from oxides and hydroxides that dissolve in water to give alkali solutions. They form the first element of a periodic, witch one outer electron, in any period from period 2 onwards. This outer electron similarly makes them behave in a chemically similar way. Some of their physical properties are typical of metals and some are not so typical of metals. Although they all have one outer electron and so similar physical and chemical properties, a characteristic of a periodic table group, but trends always go down the group. These elements are highly reactive metals. The reactivity increases on descending the Group form lithium to cesium. There is a closer similarity between the elements of this Group of the Periodic Table.

Alkali Metals are too reactive to be found free in nature. Sodium occurs mainly as NaCl (salt) in sea water and dried – up sea beds. Potassium is more widely distributed in minerals such as sulvite, KCl, but is also extracted from sea water. The alkali metals are so reactive they cannot be replaced by another element, so are isolated by electrolysis of their molten salts.

Typical metallic properties:

  • good conductors of heat and electricity
  • high boiling point
  • silvery grey surface (but rapidly tarnished by air oxidation)

When an alkali metal atoms react, it loses an electron (oxidation) to form a positively charged ion e.g. Na  Na+ + e-. In terms of electrons 2, 8, 1  2, 8 and so forming a stable ion with a noble gas electron arrangement.

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They tend react mainly with non-metals to form ionic compounds witch are usually soluble white solids.

Untypical metallic properties:

  • low melting points
  • low density (first three float on water)  
  • very soft (easily squashed, extremely malleable)
  • they have little material strength

Important trends down the group with increase in atomic number:

  • the melting point and boiling point generally decrease
  • Lithium melts at 180OC, Sodium at 98 OC, potassium at 64 OC, etc.
  • Lithium boils at 1347OC, Sodium at 883 OC, potassium at 774 OC, etc
  • The elements gets more reactive
  • … because the ...

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