C4 Chemical Patterns OCR 21st Century W Richards The Weald School 18/09/2018 18/09/2018 C4 Chemical Patterns OCR 21st Century W Richards The Weald School

C4.1 What are the patterns in properties of elements? 18/09/2018 C4.1 What are the patterns in properties of elements?

Periodic Table Introduction 18/09/2018 18/09/2018 How would you arrange these elements into groups?

Horizontal rows are called PERIODS Periodic table 18/09/2018 18/09/2018 Mendeleev The periodic table arranges all the elements in groups according to their properties. Vertical columns are called GROUPS Horizontal rows are called PERIODS

Development of the Periodic Table 18/09/2018 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.

Most of the elements are metals: The Periodic Table 18/09/2018 18/09/2018 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

Predicting Properties – the Noble Gases 18/09/2018 18/09/2018 He Ne Ar Kr Xe Rn

Properties of the Noble Gases 18/09/2018 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?

Group 1 – The alkali metals 18/09/2018 18/09/2018 Li Na K Rb Cs Fr Watch video of these metals reacting with water (from Sky One’s Brainiac)

Group 1 – The alkali metals 18/09/2018 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) + 2H2O(l) 2KOH(aq) + H2(g) Words – down, shiny, shell, hydrogen, nucleus, decreases

Properties of the Alkali Metals 18/09/2018 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 ??

Trends in Group 1 Consider a sodium atom: + 18/09/2018 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

Alkali Metals and Chlorine 18/09/2018 18/09/2018 1) Sodium and chlorine: Na + Cl - Cl Na + Sodium + chlorine sodium chloride 2) Potassium and chlorine: K K + Cl - Cl + Potassium + chlorine potassium chloride

Hazard signs to learn… Acid Corrosive Toxic h i Harmful Irritant 18/09/2018 18/09/2018 Acid Corrosive Toxic h i Harmful Irritant Oxidising

Group 7 – The halogens F Cl Br I At 18/09/2018 F Cl Br I At Some of the halogens are poisonous gases so they need to be handled in a fume cupboard!!

The Halogens - Chlorine 18/09/2018 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.

The Halogens - Bromine 18/09/2018 The forces between the diatomic molecules are slightly stronger so bromine is a liquid at room temperature. It is reddish-brown in colour.

The Halogens - Iodine 18/09/2018 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.

Properties Element Melting Point (OC) Boiling Point (OC) 18/09/2018 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 ??

Trends in Group 7 Consider a fluorine atom: - Add an electron 18/09/2018 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

Displacement reactions 18/09/2018 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

Common Molecules Chemical Diagram Formula Hydrogen H2 Water H2O 18/09/2018 Chemical Diagram Formula Hydrogen H2 Water H2O Chlorine Sodium Chloride Potassium Bromide Cl- Na+

Sodium + water sodium hydroxide + hydrogen Balancing equations 18/09/2018 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”)

Balancing equations We need to balance the equation: 18/09/2018 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) 2NaOH(aq) + H2(g)

Some examples 2 2 3 2 3 Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2 18/09/2018 2 2 3 2 3 Mg + O2 Zn + HCl Fe + Cl2 NaOH + HCl CH4 + O2 Ca + H2O NaOH + H2SO4 CH3OH + O2 MgO ZnCl2 + H2 FeCl3 NaCl + H2O CO2 + H2O Ca(OH)2 + H2 Na2SO4 + H2O 2 2 4

Balanced Equations for Alkali metals and halogens 18/09/2018 18/09/2018 Na + Cl - Cl Na + Na(s) + Cl2(g) NaCl(s) 2 2

C4.2 Explaining the Patterns in Properties 18/09/2018 C4.2 Explaining the Patterns in Properties

The structure of the atom 18/09/2018 18/09/2018 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”)

MASS NUMBER = number of protons + number of neutrons Mass and atomic number 18/09/2018 18/09/2018 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

Periodic table 18/09/2018 18/09/2018 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

Flame tests 18/09/2018 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

Using this spectroscope I can see this: Spectroscopy 18/09/2018 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.

How many protons, neutrons and electrons? Mass and atomic number 18/09/2018 18/09/2018 How many protons, neutrons and electrons? 1 11 16 H B O 1 5 8 23 35 238 Na Cl U 11 17 92

Electron structure 39 K 19 Consider an atom of Potassium: 18/09/2018 18/09/2018 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

Electron structure 14 24 40 N Mg Ca 7 12 20 18/09/2018 18/09/2018 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

Electron Structure and The Periodic Table 18/09/2018 18/09/2018 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

The Periodic Table 18/09/2018 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!

C4.3 Explaining the Properties of Compounds 18/09/2018 C4.3 Explaining the Properties of Compounds

This is called an ion (in this case, a positive hydrogen ion). Ions 18/09/2018 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).

Dissolving Ionic Structures 18/09/2018 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+

Balancing ions Some common ions: 18/09/2018 18/09/2018 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

Some examples of ionic salts 18/09/2018 Cl - Magnesium chloride: Cl Mg 2+ Mg + Cl - Cl MgCl2 Calcium oxide: O Ca + 2+ 2- CaO

Giant Ionic Structures 18/09/2018 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?

Alkali Metals and Chlorine revision 18/09/2018 18/09/2018 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