Transcript unit 1

STUDY AREA 1 – The Periodic
Table
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This area of study investigates the structure and
behaviour of atoms, they way they are arranged
in and trends across the periodic table and
introduces the concept of calculations involving
atoms.
THE KINETIC THEORY OF
MATTER
This theory explains the behaviour of atoms
whether they are in a solid, liquid or gaseous
state.
But what is the theory?
Kinetic theory states that:
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All matter is made up of tiny, invisible moving particles
Particles of different substances have different sizes
Lighter particles move faster than heavier ones at a given
temperature
As the temperature increases, the particles move faster
In a solid state, the particles are close together and vibrate in
fixed positions
In a liquid state, the particles are further apart, have more energy
and can move around each other
In a gaseous state, the particles are far apart, move rapidly and
randomly with greater energy and take up available space around
them
Atomic theory timeline
400BC: Democritus
1808: John Dalton
1897: Sir J.J Thompson
1911: Ernest Rutherford
1913: Niels Bohr
1932: Sir James Chadwick
2007: ?
Atomic structure
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What are atoms made of ?
Where do we find information about each atom
or element?
What do the numbers and symbols mean?
How are the elements arranged on the periodic
table?
electron
neutron
proton
The periodic table
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Who developed the periodic table?
What patterns exist?
Electron configuration
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Electrons are found in energy shells that
surround the nucleus (like layers around an
onion)
The shells are numbered 1 – 7 HOWEVER,
within each shell there are sub-shells which fill
up in a specific order and are lettered s, p, d & f.
To make matters more complicated, each sub
shell consists of smaller orbitals, each of which
can only hold 2 electrons.
Electron configuration
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Each shell can hold a total of 2n2 electrons
(n = shell No.)
What is the order for filling each of the sub shells?
□ 1s
□ 2s
□□□ 2p
□ 3s
□□□3p
□ 4s
□□□□□3d
□□□4p
□ 5s
Electron configuration
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Eg. Sodium (Na). Z=11 Therefore there are 11
electrons to place in energy shells. How.
Na is in period 3, therefore must occupy 3 shells.
Shell 1 = 2e, shell 2 = 8e and shell 3 = 1e
(group 1)
Written as 1s², 2s², 2p6, 3s1
Trends in the periodic table
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As you move across a period, the atomic
number increases and more electrons are being
added to the outer shell.
What trends does this produce?
What about as you move down each group.
What trends are observed?
Isotopes
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Why is the mass number for each element on
the periodic table not an even number like the
atomic number is?
Because for each atom, there are often more
than 1 isotope. An isotope is an element with
the same number of protons, but different
numbers of neutrons
Eg. O16 O17 O18
Quantities in chemistry
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Atoms are very, very, very etc. small. So how do
we calculate how much of a substance to use in
a reaction if we can’t count out a certain number
of atoms to be used.
We use the ‘mass’ instead and something called
‘a mole’
Quantities in chemistry
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When substances react, they do so in exact and
reproducible amounts.
Consider this reaction C(s) + O2(g)  CO2(g)
One atom of carbon (C) is reacting with one
molecule of oxygen (O2) to produce one
molecule of carbon dioxide (CO2).
If we knew the mass of the atoms and
molecules involved, we could predict the
quantities of reactants and products.
The ‘Mole’
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The mole is one of the most important concepts in
chemistry.
The mole is an amount of substance containing a
specified number of particles. This “specified” number
is called Avogadro's Number and is equal to
6.02 x 1023.
A mole of pure substance:-contains 6.02 x 1023
elementary particles (atoms, molecules, ions) and has a
mass (in grams) equal to its relative atomic (Ar) or
molar mass (M)
The ‘Mole’
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Calculations involving moles.
The amount of substance (in mole) can be
calculated from the mass of a pure substance
using the formula: n = m/M
Where: n is the number of moles
m is the mass in grams
M is the molar mass in g Mol-1
STUDY AREA 2 - MATERIALS
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This study area examines the different types of
bonding that can occur between substances and
how this bonding can effect the chemistry of
the substance.
Bonding
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Strong types of bonding that form molecules
include:
ionic, covalent and metallic
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Weaker forms of bonding between molecules
include:
polar, hydrogen and dispersion forces
Metallic bonding
About 80% of the known elements are metals
 Properties of Metals:
Why?
Good conductors of electricity
Good conductors of heat
Shiny (lustrous) when cleaned
Malleable
Ductile
Generally high density (all solids except mercury)
Generally high melting point
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Metallic bonding model
Metal atoms form
positive charged cations
by losing their outer shell
electrons. These
electrons hang around to
become delocalised
electrons.
Delocalised electrons can
flow throughout a metal
structure but are always
surrounding the positive
cations to keep them
balanced.
MODIFYING METALS TO MAKE
THEM MORE USEFUL
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Few metals are used in their pure form. Most
metals have been modified to improve their
performance in a particular use.
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Metals can be modified by:
alloying them
changing their crystal structure
IONIC BONDING
Ionic compounds (or salts) are usually products
of the combination of metals and non-metals.
 Properties of Ionic Compounds:
High melting temperatures (all solids at room
temperature)
Hard, but brittle
Do not conduct electricity in the solid state
Do conduct electricity when molten (or dissolved)
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THE IONIC BONDING MODEL
Na + Cl → NaCl
The Na+ and Cl- ‘ions’
arrange themselves
into a 3D crystal lattice
structure (like metals)
FORMULAE AND NAMING OF
IONIC COMPOUNDS
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What is the formula for sodium chloride?
What is the name of MgO?
What are the rules for finding the formula or
name of ionic substances?
COVALENT BONDING
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Occurs between NON METALS only
Although non metals account for only about
20% of the 100 or so elements, they combine to
form over 90% of the compounds we’ve named
to date.
There are 2 types of non metal substances:
Molecular substances
Covalent lattice substances
MOLECULAR SUBSTANCES
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Properties of Molecular Substances
Low melting and boiling points (gases or liquids
at room temperature)
Non conductors of electricity
Generally poor solubility in water
Covalent bonding model
Two fluorine atoms
can bond by
sharing their
‘unpared’ outershell
electron
Can atoms share more than
ONE electron?
Ionic V’s Covalent Bonding
Representing covalent bonds
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Covalent molecules can be drawn as either electron dot diagrams or structural
diagram
H• + H• → H:H
H + H → H-H
H
H C H
H