02/03/2016 C4 Chemical Patterns M Barker Shirebrook Academy OCR 21 st Century

02/03/2016 C4.1 What are the patterns in properties of elements?

02/03/2016 Periodic Table Introduction How would you arrange these elements into groups?

02/03/2016 Mendeleev Periodic table The periodic table arranges all the elements in groups according to their properties. Horizontal rows are called PERIODS Vertical columns are called GROUPS

02/03/2016 Development of the Periodic Table LiBeBCNOFNaMgAl LiBeBCNOFNaMgAl 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: 1864: John Newlands arranged the known elements in order of atomic mass and found out that every 8th element had similar properties: 1817: Johann Dobereiner developed the law of “triads” – he put elements together in groups of 3 according to their properties. 1913: Henry Moseley proposed the use of atomic number rather than atomic mass.

02/03/2016 HHe LiBeBCNOFNe NaMgAlSiPSClAr KCaFeNiCuZnBrKr AgIXe PtAuHg The Periodic Table Most of the elements are metals: These elements are metals This line divides metals from non- metals These elements are non-metals

02/03/2016 Predicting Properties – the Noble Gases He Ne Ar Kr Xe Rn

02/03/2016 Properties of the Noble Gases ElementMelting Point ( O C)Boiling Point ( O C)Density (g/dm 3 ) Helium Neon Argon Krypton Xenon??? What numbers would you expect Xenon to have?

02/03/2016 Group 1 – The alkali metals Li Na K Rb Cs Fr Watch video of these metals reacting with water (from Sky One’s Brainiac)

02/03/2016 Group 1 – The alkali metals 1) These metals are _____ when freshly cut but quickly tarnish due to reacting with water vapour Some facts… 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 Potassium + water potassium hydroxide + hydrogen 2K (s) + 2H 2 O (l) 2KOH (aq) + H 2(g) 2) Density increases as you go down the group, while melting point ________

02/03/2016 Properties of the Alkali Metals ElementMelting Point ( O C)Boiling Point ( O C)Density (g/cm 3 ) Lithium Sodium Potassium Rubidium Caesium??

02/03/2016 Trends in Group 1 Consider a sodium atom: Take away one of the electrons + + Now consider a potassium atom: Sodium ion Potassium ion Take away one of the electrons Potassium loses its electron more easily because its further away – potassium is MORE REACTIVE

02/03/2016 Alkali Metals and Chlorine 1) Sodium and chlorine: K + Cl - Na Cl + 2) Potassium and chlorine: Cl + Sodium + chlorine sodium chloride Potassium + chlorine potassium chloride K Na + Cl -

02/03/2016 Hazard signs to learn… hi Acid HarmfulIrritant Corrosive Oxidising Toxic

02/03/2016 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!!

02/03/2016 The Halogens - Chlorine 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.

02/03/2016 The Halogens - Bromine The forces between the diatomic molecules are slightly stronger so bromine is a liquid at room temperature. It is reddish-brown in colour.

02/03/2016 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.

02/03/2016Properties ElementMelting Point ( O C)Boiling Point ( O C)Density (g/cm 3 ) Flourine Chlorine Bromine Iodine Astatine??

02/03/2016 Trends in Group 7 Consider a fluorine atom: Add an electron - - Now consider a chlorine atom: Flouride ion Chloride ion Add an electron Chlorine doesn’t gain an electron as easily as fluorine so it is LESS REACTIVE

02/03/2016 Displacement reactions To put it simply, a MORE reactive halogen will displace a LESS reactive halogen from a solution of its salt. F Cl Br I Decreasing reactivity Potassium chloride KCl (aq) Potassium bromide KBr (aq) Potassium iodide KI (aq) Chlorine Cl 2 Bromine Br 2 Iodine I 2

02/03/2016 Common Molecules ChemicalDiagramFormula HydrogenH2H2 WaterH2OH2O Chlorine Sodium Chloride Potassium Bromide Cl - Na + Cl - Na + Cl - Na + Cl - Na +

02/03/2016 Balancing equations Consider the following reaction: Na O HH HH O H Sodium + water sodium hydroxide + hydrogen + + 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”)

02/03/2016 Balancing equations We need to balance the equation: Na O HH HH O H Sodium + water sodium hydroxide + hydrogen + + Na O HH O H Now the equation is balanced, and we can write it as: 2Na (s) + 2H 2 O (l) 2NaOH (aq) + H 2(g)

02/03/2016 Some examples Mg + O 2 Zn + HCl Fe + Cl 2 NaOH + HCl CH 4 + O 2 Ca + H 2 O NaOH + H 2 SO 4 CH 3 OH + O 2 MgO ZnCl 2 + H 2 FeCl 3 NaCl + H 2 O CO 2 + H 2 O Ca(OH) 2 + H 2 Na 2 SO 4 + H 2 O CO 2 + H 2 O

02/03/2016 Balanced Equations for Alkali metals and halogens Na Cl + Na (s) + Cl 2(g) NaCl (s) Na + Cl - 22

02/03/2016 C4.2 Explaining the Patterns in Properties

02/03/2016 The structure of the atom ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron ( “ 1 ” ) NEUTRON – neutral, same mass as proton ( “ 1 ” ) 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

02/03/2016 Mass and atomic number ParticleRelative MassRelative Charge Proton1+1 Neutron10 ElectronVery small MASS NUMBER = number of protons + number of neutrons SYMBOL PROTON NUMBER = number of protons (same as the number of electrons) - this number stays the same for a given element

02/03/2016 Mendeleev Periodic table etc Notice that elements in the Periodic Table are arranged in order of proton number: Proton number

02/03/2016 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

02/03/2016Spectroscopy 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.

02/03/2016 Mass and atomic number How many protons, neutrons and electrons?

02/03/2016 Electron structure Consider an atom of Potassium: Potassium has 19 electrons. These electrons occupy specific energy levels “ shells ” … Nucleus The inner shell has __ electrons The next shell has __ electrons The next shell has the remaining __ electron Electron structure = 2,8,8,1

02/03/2016 Electron structure Draw the electronic structure of the following atoms: Electron structure = 2,8,8,2 Nucleus Electron structure = 2,8,2 Nucleus Electron structure = 2,5 Nucleus

02/03/2016 HHe LiBeBCNOFNe NaMgAlSiPSClAr KCaFeNiCuZnBrKr AgIXe PtAuHg Electron Structure and The Periodic Table 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?

02/03/2016 HHe LiBeBCNOFNe NaMgAlSiPSClAr KCaFeNiCuZnBrKr AgIXe PtAuHg The Periodic Table The chemical properties of each element are determined by its electron arrangement, e.g: Potassium has 19 electrons in the configuration __,__,__,__ Sodium has 11 electrons in the configuration 2,8,1 Potassium is more reactive as it’s outer electron is further away from the nucleus. The halogens have 7 electrons in their outer shell so they have totally different properties!

02/03/2016 C4.3 Explaining the Properties of Compounds

02/03/2016Ions An ion is formed when an atom gains or loses electrons and becomes 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) The electron is negatively charged The proton is positively charged +

02/03/2016 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 +

02/03/2016 Balancing ions Determine the formula of these compounds: 1)Sodium chloride 2)Magnesium oxide 3)Magnesium chloride 4)Ammonium chloride 5)Sodium sulphate 6)Sodium oxide Some common ions: Sodium – Na + Potassium – K + Magnesium – Mg 2+ Ammonium – NH 4 + Chloride – Cl - Bromide – Br - Oxide – O 2- Sulphate – SO 4 2- Answers: 1)NaCl 2)MgO 3)MgCl 2 4)NH 4 Cl 5)Na 2 SO 4 6)NaO

02/03/2016 Some examples of ionic salts Mg Magnesium chloride: MgCl 2 Cl + Mg 2+ Cl - - Calcium oxide: CaO O Ca + 2+ O 2-

02/03/2016 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). Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - Na + Cl - If these ions are strongly held together what affect would this have on the substance’s: 1)Melting point? 2)Boiling point? 3)State (solid, liquid or gas) at room temperature?

02/03/2016 Alkali Metals and Chlorine revision 1) Sodium and chlorine: K + Cl - Na Cl + 2) Potassium and chlorine: Cl + Sodium + chlorine sodium chloride Potassium + chlorine potassium chloride K Na + Cl - Notice that these compounds are “ionic”