# 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)

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