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2 Atomic Structure

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Title: 2 Atomic Structure


1
2 Atomic Structure
2
Properties of subatomic particles
Name Relative charge Relative mass(amu) Location
Proton 1 1 nucleus
Neutron 0 1 nucleus
Electron -1 0 Outside nucleus
3
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

4
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
5
  • 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
6
(No Transcript)
7
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-

8
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

9
  • 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
10
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)

11
Formation of Covalent BondsDrawing dot and cross
diagrams
  • Only outer shell electrons are shown
  • Dots and crosses used to distinguish electrons
    from different atoms

12
Formation of HCl
o
o
o
x
o
o
o
o
H
Cl
o
o
o
x
o
o
o
o
HCl
13
  • Draw dot and cross diagrams for methane (CH4),
    ammonia (NH3) and nitrogen N2 and carbon dioxide
    (CO2)

14
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-

15
o
o
x
o
  • Na Cl

o
o
o
o
Na Cl-
NaCl
16
x
x
o
o
  • Mg F

o
o
F
Mg2 2F-
MgF2
17
  • Draw diagrams to represent the ionic bonding for
    aluminium iodide and sodium oxide

18
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

19
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

20
  • 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

21
Diamond Structure
22
Properties of Simple Covalent Compounds
  • Low mp/bp
  • Non conducting
  • Soluble in non-polar solvents
  • Solids are soft

23
Properties of Giant Covalent Structures
  • High mp/bp
  • Non-conducting (except graphite and some
    semiconductors e.g. silicon dioxide)
  • Non-soluble
  • Hard (except graphite)
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