Structures and Bonding

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22/06/2016
C4 Chemical Patterns
OCR 21st Century
W Richards The Weald School
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C4.1 What are the patterns in properties of
elements?
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Periodic Table Introduction
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How would you arrange these elements into groups?
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Periodic table
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Horizontal rows are called PERIODS
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Development of the Periodic Table
Li Be B C N O F Na Mg Al
Li Be B C N O F Na Mg Al
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The Periodic Table
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Most of the elements are metals
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Fe Ni Cu Zn Br Kr
Ag I Xe
Pt Au Hg

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Predicting Properties the Noble Gases
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He
Ne
Ar
Kr
Xe
Rn







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Properties of the Noble Gases
Element Melting Point (OC) Boiling Point (OC) Density (g/dm3)
Helium -272 -269 0.1786
Neon -249 -246 0.9002
Argon -189 -186 1.784
Krypton -157 -153 3.749
Xenon ? ? ?
What numbers would you expect Xenon to have?
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Group 1 The alkali metals
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Li
Na
K
Rb
Cs
Fr







Watch video of these metals reacting with water
(from Sky Ones Brainiac)
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Group 1 The alkali metals
Some facts







1) These metals are _____ when freshly cut but
quickly tarnish due to reacting with water vapour
2) Density increases as you go down the group,
while melting point ________
3) Reactivity increases as you go _______ the
group. This is because the electrons are further
away from the _______ every time a _____ is
added, so they are given up more easily.
4) They all react with water to form an alkali
(hence their name) and __________. This means
they need to be stored under oil.
Words down, shiny, shell, hydrogen, nucleus,
decreases
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Properties of the Alkali Metals
Element Melting Point (OC) Boiling Point (OC) Density (g/cm3)
Lithium 180 1340 0.53
Sodium 98 883 0.97
Potassium 64 760 0.86
Rubidium 39 688 1.53
Caesium ?? ?? ??
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Trends in Group 1
Consider a sodium atom
Sodium ion
Now consider a potassium atom
Potassium ion
Potassium loses its electron more easily because
its further away potassium is MORE REACTIVE
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Alkali Metals and Chlorine
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1) Sodium and chlorine

2) Potassium and chlorine

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Hazard signs to learn
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Acid
Corrosive
Toxic
Harmful
Irritant
Oxidising
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Group 7 The halogens
F
Cl
Br
I
At








Some of the halogens are poisonous gases so they
need to be handled in a fume cupboard!!
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The Halogens - Chlorine
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The Halogens - Bromine
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The Halogens - Iodine
Iodine is a solid at room temperature but with
gentle heating it will melt. The atoms will
remain in pairs. In solid form iodine is grey
like metal but gaseous iodine is purple.
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Properties
Element Melting Point (OC) Boiling Point (OC) Density (g/cm3)
Flourine -220 -188 0.0016
Chlorine -101 -34 0.003
Bromine -7 59 3.12
Iodine 114 184 4.95
Astatine ?? ?? ??
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Trends in Group 7
Consider a fluorine atom
Flouride ion
Now consider a chlorine atom
Chloride ion
Chlorine doesnt gain an electron as easily as
fluorine so it is LESS REACTIVE
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Displacement reactions
To put it simply, a MORE reactive halogen will
displace a LESS reactive halogen from a solution
of its salt.
Potassium chloride KCl(aq) Potassium bromide KBr(aq) Potassium iodide KI (aq)
Chlorine Cl2
Bromine Br2
Iodine I2
F
Cl
Br
I
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Common Molecules
Chemical Diagram Formula
Hydrogen H2
Water H2O
Chlorine
Sodium Chloride
Potassium Bromide
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Balancing equations
Consider the following reaction


This equation doesnt balance there are 2
hydrogen atoms on the left hand side (the
reactants and 3 on the right hand side (the
products)
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Balancing equations
We need to balance the equation


Now the equation is balanced, and we can write it
as
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Some examples
2 2 2 3
2 2 2 2 3
2 2 2 2 2 4
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Balanced Equations for Alkali metals and halogens
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2
2
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C4.2 Explaining the Patterns in Properties
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The structure of the atom
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I did some experiments in 1808 that proved this
and called these particles ATOMS. Most of an
atom is empty space and the nucleus is actually
very small so this diagram is wrong
Dalton
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Mass and atomic number
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Particle Relative Mass Relative Charge
Proton 1 1
Neutron 1 0
Electron Very small -1
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Periodic table
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Notice that elements in the Periodic Table are
arranged in order of proton number
1 2
3 4 5 6 7 8 9 10
11 12 13 14 15 16 17 18
19 20 21 22 etc



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Flame tests
Compounds containing lithium, sodium, potassium,
calcium and barium ions can be recognised by
burning the compound and observing the colours
produced
Lithium Red
Sodium Yellow
Potassium Lilac
Calcium Brick red
Barium Green
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Spectroscopy
Spectroscopy is kind of like a flame test but
using a spectroscope to see the results
Using this spectroscope I can see this
Each different element has a different
signature when viewed through a spectroscope.
This analysis enables us to the discovery of new
elements including rubidium and caesium and these
discoveries depended on these new techniques.
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Mass and atomic number
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How many protons, neutrons and electrons?
1
11
16
H
B
O
1
5
8
23
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238
Na
Cl
U
11
17
92
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Electron structure
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Consider an atom of Potassium
Potassium has 19 electrons. These electrons
occupy specific energy levels shells
The inner shell has __ electrons The next shell
has __ electrons The next shell has __
electrons The next shell has the remaining __
electron
Electron structure 2,8,8,1
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Electron structure
22/06/2016
Draw the electronic structure of the following
atoms
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24
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Ca
Mg
N
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20
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Electron structure 2,8,8,2
Electron structure 2,8,2
Electron structure 2,5
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Electron Structure and The Periodic Table
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Looking at their position in the Periodic Table
gives us the key to work out an elements
electron structure
How many electrons do the noble gases and
halogens have in their outer shell?
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Fe Ni Cu Zn Br Kr
Ag I Xe
Pt Au Hg

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The Periodic Table
The chemical properties of each element are
determined by its electron arrangement, e.g
Potassium is more reactive as its outer electron
is further away from the nucleus.
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Fe Ni Cu Zn Br Kr
Ag I Xe
Pt Au Hg

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C4.3 Explaining the Properties of Compounds
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Ions
An ion is formed when an atom gains or loses
electrons and becomes charged
If we take away the electron were left with
just a positive charge
This is called an ion (in this case, a positive
hydrogen ion).
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Dissolving Ionic Structures
When an ionic structure like sodium chloride is
dissolved it enables the water to conduct
electricity this gives evidence of the
existence of ions
Cl-
Na
Cl-
Na
Cl-
Na
Cl-
Na
Cl-
Na
Cl-
Na
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Balancing ions
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• Determine the formula of these compounds
• Sodium chloride
• Magnesium oxide
• Magnesium chloride
• Ammonium chloride
• Sodium sulphate
• Sodium oxide

• Answers
• NaCl
• MgO
• MgCl2
• NH4Cl
• Na2SO4
• NaO

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Some examples of ionic salts
Magnesium chloride

MgCl2
Calcium oxide
CaO
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Giant Ionic Structures
When many positive and negative ions are joined
they form a giant ionic lattice where each ion
is held to the other by strong electrostatic
forces of attraction (ionic bonds).

• If these ions are strongly held together what
  affect would this have on the substances
• Melting point?
• Boiling point?
• State (solid, liquid or gas) at room temperature?

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Alkali Metals and Chlorine revision
22/06/2016
Notice that these compounds are ionic
1) Sodium and chlorine

2) Potassium and chlorine