1. C4 Chemical Patterns OCR 21st Century W Richards The Weald School
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C4 Chemical Patterns
OCR 21st Century
W Richards
The Weald School

2. C4.1 What are the patterns in properties of elements?
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C4.1 What are the patterns in properties of elements?

3. Periodic Table Introduction
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How would you arrange these elements into groups?

4. Horizontal rows are called PERIODS
Periodic table
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Mendeleev
The periodic table arranges all the elements in groups according to their properties.
Vertical columns are called GROUPS
Horizontal rows are called PERIODS

5. Development of the Periodic Table
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1817: Johann Dobereiner developed the law of “triads” – he put elements together in groups of 3 according to their properties.
1864: John Newlands arranged the known elements in order of atomic mass and found out that every 8th element had similar properties: Li Be B C N O F Na Mg Al
1869: Dimitri Mendeleev arranged the known elements in order of mass but he also left in gaps and was able to predict the properties of unknown elements: Li Be B C N O F Na Mg Al
1913: Henry Moseley proposed the use of atomic number rather than atomic mass.

6. Most of the elements are metals:
The Periodic Table
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Most of the elements are metals:
These 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
These elements are non-metals
This line divides metals from non-metals

7. Predicting Properties – the Noble Gases
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8. Properties of the Noble Gases
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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?

9. Group 1 – The alkali metals
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Watch video of these metals reacting with water (from Sky One’s Brainiac)

10. Group 1 – The alkali metals
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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.
Potassium + water potassium hydroxide + hydrogen
2K(s) H2O(l) KOH(aq) H2(g)
Words – down, shiny, shell, hydrogen, nucleus, decreases

11. Properties of the Alkali Metals
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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 ??

12. Trends in Group 1 Consider a sodium atom: +
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Consider a sodium atom: +
Take away one of the electrons
Sodium ion
Now consider a potassium atom: +
Take away one of the electrons
Potassium ion
Potassium loses its electron more easily because its further away – potassium is MORE REACTIVE

13. Alkali Metals and Chlorine
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1) Sodium and chlorine: Na + Cl - Cl Na +
Sodium + chlorine sodium chloride
2) Potassium and chlorine: K K + Cl - Cl +
Potassium + chlorine potassium chloride

14. Hazard signs to learn… Acid Corrosive Toxic h i Harmful Irritant
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Acid
Corrosive
Toxic h i
Harmful
Irritant
Oxidising

15. Group 7 – The halogens F Cl Br I At
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Some of the halogens are poisonous gases so they need to be handled in a fume cupboard!!

16. The Halogens - Chlorine
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Each molecule has a strong force holding the atoms together (forming a “diatomic molecule”), but the forces between molecules are very weak so chlorine is a gas at room temperature and is pale yellow.

17. The Halogens - Bromine
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The forces between the diatomic molecules are slightly stronger so bromine is a liquid at room temperature. It is reddish-brown in colour.

18. The Halogens - Iodine
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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.

19. Properties Element Melting Point (OC) Boiling Point (OC)
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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 ??

20. Trends in Group 7 Consider a fluorine atom: - Add an electron
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Consider a fluorine atom: -
Add an electron
Flouride ion
Now consider a chlorine atom: -
Add an electron
Chloride ion
Chlorine doesn’t gain an electron as easily as fluorine so it is LESS REACTIVE

21. Displacement reactions
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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
Decreasing reactivity

22. Common Molecules Chemical Diagram Formula Hydrogen H2 Water H2O
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Chemical
Diagram
Formula
Hydrogen H2
Water
H2O
Chlorine
Sodium Chloride
Potassium Bromide
Cl-
Na+

23. Sodium + water sodium hydroxide + hydrogen
Balancing equations
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Consider the following reaction:
Sodium + water sodium hydroxide + hydrogen Na O H O H Na + H +
This equation doesn’t balance – there are 2 hydrogen atoms on the left hand side (the “reactants” and 3 on the right hand side (the “products”)

24. Balancing equations We need to balance the equation:
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We need to balance the equation:
Sodium + water sodium hydroxide + hydrogen Na O H O H Na O H Na O H + H + Na
Now the equation is balanced, and we can write it as:
2Na(s) + 2H2O(l) NaOH(aq) + H2(g)

25. Some examples 2 2 3 2 3 Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2
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Mg O2
Zn HCl
Fe Cl2
NaOH HCl
CH O2
Ca H2O
NaOH H2SO4
CH3OH O2
MgO
ZnCl H2
FeCl3
NaCl H2O
CO H2O
Ca(OH) H2
Na2SO H2O 2

26. Balanced Equations for Alkali metals and halogens
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Na(s) + Cl2(g) NaCl(s) 2 2

27. C4.2 Explaining the Patterns in Properties
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C4.2 Explaining the Patterns in Properties

28. 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
ELECTRON – negative, mass nearly nothing
PROTON – positive, same mass as neutron (“1”)
NEUTRON – neutral, same mass as proton (“1”)

29. MASS NUMBER = number of protons + number of neutrons
Mass and atomic number
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Particle
Relative Mass
Relative Charge
Proton 1 +1
Neutron
Electron
Very small -1
MASS NUMBER = number of protons + number of neutrons He 2 4
SYMBOL
PROTON NUMBER = number of protons (same as the number of electrons) - this number stays the same for a given element

30. Periodic table
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Mendeleev
Notice that elements in the Periodic Table are arranged in order of proton number:
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

31. Flame tests
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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

32. Using this spectroscope I can see this:
Spectroscopy
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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.

33. How many protons, neutrons and electrons?
Mass and atomic number
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How many protons, neutrons and electrons? 1 11 16 H B O 1 5 8 23 35
238 Na Cl U 11 17 92

34. Electron structure 39 K 19 Consider an atom of Potassium:
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Consider an atom of Potassium:
Nucleus K 19 39
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 the remaining __ electron
Electron structure
= 2,8,8,1

35. Electron structure 14 24 40 N Mg Ca 7 12 20
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Draw the electronic structure of the following atoms: 14 24 40 N Mg Ca 7 12 20
Nucleus
Nucleus
Nucleus
Electron structure
= 2,5
Electron structure
= 2,8,2
Electron structure
= 2,8,8,2

36. 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 element’s electron structure:
For example, group 1 elements all have 1 electron in their outer shell
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

37. The Periodic Table
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The chemical properties of each element are determined by its electron arrangement, e.g:
Potassium is more reactive as it’s 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
Sodium has 11 electrons in the configuration 2,8,1
Potassium has 19 electrons in the configuration __,__,__,__
The halogens have 7 electrons in their outer shell so they have totally different properties!

38. C4.3 Explaining the Properties of Compounds
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C4.3 Explaining the Properties of Compounds

39. This is called an ion (in this case, a positive hydrogen ion).
Ions
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An ion is formed when an atom gains or loses electrons and becomes charged: + -
The electron is negatively charged
The proton is positively charged + +
If we “take away” the electron we’re left with just a positive charge:
This is called an ion (in this case, a positive hydrogen ion).

40. Dissolving Ionic Structures
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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+

41. Balancing ions Some common ions:
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Some common ions:
Sodium – Na+
Potassium – K+
Magnesium – Mg2+
Ammonium – NH4+
Chloride – Cl-
Bromide – Br-
Oxide – O2-
Sulphate – SO42-
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

42. Some examples of ionic salts
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Magnesium chloride: Cl Mg 2+ Mg + Cl - Cl
MgCl2
Calcium oxide: O Ca + 2+ 2-
CaO

43. Giant Ionic Structures
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Cl-
Na+
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 substance’s:
Melting point?
Boiling point?
State (solid, liquid or gas) at room temperature?

44. Alkali Metals and Chlorine revision
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Notice that these compounds are “ionic”
1) Sodium and chlorine: Na + Cl - Cl Na +
Sodium + chlorine sodium chloride
2) Potassium and chlorine: K K + Cl - Cl +
Potassium + chlorine potassium chloride