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Atomic Structure 2 Atomic

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					2 Atomic Structure
  Properties of subatomic particles
Name       Relative   Relative    Location
           charge     mass(amu)
Proton     +1         1           nucleus


Neutron    0          1           nucleus


Electron   -1         0           Outside
                                  nucleus
      Terminology for the Atom
• Atomic no (Z): no of protons
• Mass No (A): no of protons + no of neutrons
• Isoptopes: atoms of the same number of protons (the
  same element) but different numbers of neutrons
• Atomic mass unit: 1/12 the mass of a carbon-12 atom.
  The mass of a carbon-12 atom is defined as exactly 12
  atomic mass units
• Atomic mass: the average of the masses of an elements
  naturally occurring isotopes weighted to their
  abundances
         Isotope Calculations
• Boron has 2 isotopes 10B and 11B. They
  are present in naturally occurring boron
  respectively at 18.7% and 81.3%.
  Calculate the relative atomic mass of
  boron.
   Ar = (18.7 x 10) + (81.3 x 11)
                  100

        = 10.8
• The element copper has relative atomic
  mass 63.55 and contains atoms with mass
  numbers 63 and 65. What is the
  percentage composition of a normal
  isotope of copper?
 65x + ((100-x) x 63) = 63.55
         100

 65x + 6300 – 63x = 6355

 2x = 6355-6300
 x = 27.5%
 100 – x = 72.5%
 % composition = 27.5% 65Cu 72.5% 63Cu
          Bonding Terminology
• Ionic compounds: form when an atom of one element
  transfers electrons to an atom of another element
• Covalent compounds: form when two atoms share
  electrons
• Ion: a charged particle
• Cation: a positively charged particle
• Anion: a negatively charged particle
• Monoatomic ion: an ion composed of a single aton
• Polyatomic ion: two or more atoms bonded covalently
  and having net positive or negative charge e.g. NH4+,
  SO42-
     Electronic Configuration
• Electrons are present in shells around the
  nucleus
• The first shell can hold 2 electrons, the
  second 8 and the third 18
• The no of outer shell electrons is the same
  as the group no
Find the electronic configuration of sodium
  Na atomic no = 11  there are 11 protons and 11
  electrons
  Electronic Configuration is 2,8,1



Find the electronic configuration of chlorine

 Cl atomic no = 17  there are 17 protons and 17
 electrons
 Electronic configuration is 2,8,7
            Compounds
• Ionic compounds are formed between a
  metal and a non metal e.g. magnesium
  chloride
• Covalent compounds are formed between
  two or more non-metals e.g ammonia
  (NH3)
       Formation of Covalent Bonds
      Drawing dot and cross diagrams


• Only outer shell electrons are shown
• Dots and crosses used to distinguish
  electrons from different atoms
    Formation of HCl
                             o o

                                   o
     x                 o           o


                             o o
H                            Cl

                       o o

               x             o
               o             o


                       o o
              HCl
• Draw dot and cross diagrams for methane
  (CH4), ammonia (NH3) and nitrogen N2 and
  carbon dioxide (CO2)
     Formation of ionic bonds
• Elements    in Group 1 form unipositive cations
  e.g. Na+
• Elements    in Group 2 form dipositive cations e.g.
  Mg2+
• Elements    in Group 3 form tripositive cations e.g.
  Al 3+
• Elements    in Group 7 form uninegative anions
  e.g. Cl-1
• Elements    in Group 6 form dinegative anions e.g.
  O2-
                       oo
     x                       o
Na                    o Cl   o
                        oo




         Na+    +     Cl-



               NaCl
 xx             oo
Mg              Fo
               o o
                oo

                oo
                     o
               oF    o
                oo




      Mg2+ +   2F-       MgF2
• Draw diagrams to represent the ionic
  bonding for aluminium iodide and sodium
  oxide
Properties of Ionic Compounds
• High mp/bp
• Conduct electricity when molten or in
  aqueous solution
• Dissolve in polar solvents (eg water)
• Hard and brittle
• React readily with each other in solution
         Covalent Compounds
             & Structures
• Covalent compounds may be classed as
  simple e.g water, ammonia, chlorine,
  sulphur dioxide, carbon dioxide

• or as giant e.g. silicon dioxide (sand)
  diamond, graphite
• Simple covalent compounds are small
  molecules held together by Van der Waals
  forces only



• Giant covalent structures are giant lattices
  where every atom is covalently bonded to
  many atoms
Diamond Structure
     Properties of Simple Covalent
              Compounds
•   Low mp/bp
•   Non conducting
•   Soluble in non-polar solvents
•   Solids are soft
    Properties of Giant Covalent
             Structures
• High mp/bp
• Non-conducting (except graphite and
  some semiconductors e.g. silicon dioxide)
• Non-soluble
• Hard (except graphite)