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)