JM 2 C ER H G I H HC l 1 2 3 4 5 6 7 8 CuSO 4 9 10 11 12 13
14 CH 4 Al2 O3 NaCl Atomic Structure An atoms nucleus contains protons and neutrons. Electrons orbit the nucleus in shells Same number of electrons and protons. Sub-atomic Particle Mass Charge Proton 1 + Electron Almost 0 - Neutron
1 0 Mass Number Atomic Number 12 6 C Electron Arrangement Maximum of 2 in the first shell, 8 in subsequent shell Electron arrangement in carbon: Electron configuration = [2, 4] Elements with a full outer shell are unreactive Horizontal rows periods: as we move one across the electron number increases by one. Vertical rows groups: elements in a vertical row have similar chemical Ionic Bonds Ionic Bonding between metals and non-metals Involves giving and receiving of electrons in order to fill up outer shells like noble gases example: Sodium 2,8,1 looses one electron (easier
to lose one electron than to gain seven) When an atom looses an electron they are left with one more proton in the nucleus than electrons orbiting the nucleus. This makes sodium have a plus charge (Na+). During chemical bonding ions are formed. There is a quick way to work out what the charge on an ion should be: the number of charges on an ion formed by a metal is equal to the group number of the metal the number of charges on an ion formed by a nonmetal is equal to the group number minus eight E.g. hydrogen forms H+ ions, magnesium forms Mg2+ ions Ionic bonding can be represented by dot and cross diagrams Covalent Covalent Bonds Bonding between non-metals and non-metals The atoms share electrons in order to complete their outer shells. The atoms all attain noble gas structure (complete outer shells). The new particles formed are neutral
Methanemolecules. Structures of Substances There are four main structures of substances: Simple Molecular Giant Ionic Giant Covalent Giant Metallic Simple Molecular Structures Small molecules containing few atoms (e.g. H2O, CO2) Contain strong covalent bonds Forces between atoms are super-strong Forces between molecules are fairly weak Typical Properties: Low melting point and boiling point Do not conduct electricity Tend to have little strength (soft) Giant Ionic Structures Ions held together by strong attraction Forces equal in all directions in lattice Tightly packed ions Strong forces between ions Structures of Substances Ionic substances conduct electricity when they are molten because the ions are free to move around
Many can also be dissolved in water, where they will also conduct electricity (e.g. NaCl) Giant Covalent Structures Large network of bonds giant covalent Substances such as: diamond, graphite and silicon dioxide Held together in many strong covalent bonds They are hard High melting and boiling points Unreactive chemically Graphite has free electrons delocalised electrons conduct electricity. Fullerenes: carbons ability to make large cage like structures. Important in nanoscience and industry Diamond Graphite Sand Carbon based Carbon based Carbon based Each C joins to 4 others Each C joins to 3 others Each silicon joins to 4oxygen VERY hard 1 free electron per carbon
Each oxygen joined to 2 silico No electrical conductivity Thus, conducts electricity Structures of Substances Giant Metallic Structures The atoms in metals are in layers which can slide over each other, this makes it possible to bend them or beat them into shape. The atoms in metals share their outer electrons with all the other metal atoms, so that a metal consists of positive ions held together by free electrons which can move throughout the structure. Like other giant structures, the forces (called metallic bonds) holding the atoms together are very strong. The main properties of metals are: 1) Metals are strong. 2) Most metals have high melting points. 3) Metals are malleable (they can be bent of beaten into different shapes) 4) Metals are good conductors of electricity & heat 5) Metals are lustrous (shiny) Masses and Moles Formula masses (Ar and Mr) The Ar is the relative atomic mass in the periodic table. The Ar values of the atoms in a formula are added to get the formula mass or Mr (sometimes called molecular mass) H2SO4 = 1x2 + 32 + 16x4 = 98 Mg(NO3)2 = 24 + (14 + 3x16)x2 = 148 Percentage Calculations If you need to find the percentage of an element in a compound, you use the formula:
Percentage = Ar x No of atoms x 100 Mr of compound e.g. Find the percentage of nitrogen in ammonium nitrate (NH4NO3) Mr of N = 15 No of N atoms = 2 Mr of ammonium nitrate = 14 + 4 x 1+ 14 + 3 x 16 = 80 Percentage of nitrogen = 2x14x 100 = 35% 80 Empirical Formulae This is the formula which shows the lowest whole number ratio of the atoms e.g. Molecular formula = C2H4, Empirical Formula = CH2 To calculate an empirical formula Find the mass (or %) of each element present Divide each of these masses by the relative mass of that element Divide each number obtained in stage 2 by the smallest of those numbers. This should give whole numbers which can be used in the empirical formula. Masses and Moles 20g of a compound of Silicon with hydrogen contains 17.5g of silicon. Find the empirical
formula. Element Si H Mass of element present 17.5 20-17.5 = 2.5 Relative Mass (Ar) Mass Ar 28 17.528 = 0.625 1 2.51 = 2.5 Divide through by smallest. 0.625 0,625 = 1 2.5 0.625 = 4 Whole Number Ratio Empirical Formula 1
4 SiH4 Equation Calculations In these, you will always be given the mass of one substance and be asked to find the mass of another substance MOLES; MOLES; MASS !! Mass Moles of the one you know Moles of the one you dont Now work out the unknown massMr Moles Masses and Moles What mass of carbon dioxide is obtained by burning 3g of C2H6? 2C2H6 + 7O2 = 4CO2 + 6H2O Mass Mr: C2H6 = 30, CO2 = 44 Mr Moles of C2H6 = Mass = 3 = 0.1 Mr 30 Moles Moles of CO2 = Moles of C2H6 x 2 = 0.2 Mass of CO2 = Mr x Moles = 44 x 0.2 = 8.8g
Atom Economy This is given as Formula Mass of all molecules of Useful Product x 100 Formula Mass of all molecules of Reactants Eg. Atom economy for making iron from the equation Fe2O3 + 3CO = 2Fe + 3CO2 (Mr : Fe2O3 =160, CO = 28, Fe = 56, CO2 =44) Mass of useful product (iron atoms) = 2x56 =112 Mass of all reactants = 160 + (3x28) = 244 Atom economy = 112 x 100 244 = 45.9% Chromatography and GC-MS Paper chromatography is a form of separation that allows analysis of food additives or dyes in pens. Instrumental methods: Great for analysis of small amounts Gas Chromatography linked to Mass Rapid Sensitive Spectroscopy (GC-MS) is an example of an instrumental method
Accurate Gas chromatography allows the separation of a mixture of compounds The time taken for a substance to travel through the column helps to identify the substance The mass spectrometer attached to the gas chromatography column allows the mass of the substance to be observed as it leaves the column, which also helps to identify the substance The mass spectrometer can also give the relative molecular mass (Mr) of each substance separated this is seen at the molecular ion peak. Polymers The properties of polymers depend on what they are made of and by which method they are made. High and low densities of polymer are made using different reactions and catalysts. Low Density High Density There are two types of plastic: Thermosoftening Individual tangled polymer strands. Melt when heated. Thermosetting Polymer chains with cross links between them. Do not melt
when heated. Nano Science A nanometre (nm), is one billionth of a metre (or a millionth of a millimetre). Nanoparticles range in size from about 100nm down to about 1nm. Nanoparticles have a very large surface area compared with their volume, so they are often able to react very quickly. They can, for example, be used in self-cleaning ovens and windows. Nanoparticles also have different properties to the same substance in normal-sized pieces. For example, titanium dioxide is a white solid used in house paint and certain sweet-coated chocolates. BUT, titanium dioxide nanoparticles cannot be seen as they are too small to reflect visible light. They are used in sun screens to block harmful ultraviolet light without appearing white on the skin. Future developments in nanoscience might include: New catalysts New coatings New computers Stronger and lighter building materials Sensors that detect individual substances in tiny amounts Electrolysis Conductors
Metals and graphite are the only solids which conduct electricity, but no chemical change is involved. Liquid (melted) metals also conduct, but again there is no chemical change. Electrolytes These are liquids which conduct electricity, and are decomposed by it. They are ionic substances which are dissolved in water or have been melted. This includes all acids and metal compounds. Examples: Copper sulphate solution, iron chloride solution, molten sodium chloride, dilute sulphuric acid. Non-electrolytes are covalent substances, e.g. pure water, sugar solution, alcohol, petrol. Electrolysis This is when an electric current passes through an electrolyte. Electrons enter the solution through the negative electrode (cathode), cause a chemical change and leave by the positive electrode (anode). Molten electrolytes are split into their elements by electrolysis. The metal is produced at the cathode (-), while the nonmetal is produced at the anode (+) e.g. Lead Bromide (molten) = Lead (at the cathode) + Bromine (at the anode) PbBr2 PB (I) + BR2 (g) Electrolysis With aqueous electrolytes, the electrolyte is also split
up, but if the metal is reactive, then hydrogen from the water is produced at the cathode in place of the metal. e.g. Copper chloride (aq) = Copper (at the cathode) + Chlorine (at the anode) e.g. Sodium chloride (aq) = Hydrogen (at the cathode) + Chlorine (at the anode) Because positive ions go to the cathode, they are called Cations Because negative ions go to the anode, they are called Anions Anion Cation Electrolysis Change at the electrodes During electrolysis ions move towards the electrodes. When an ion reaches the electrode they either lose or gain an electron depending on their charge. Negatively charged ions lose electrons to become neutral atoms Positively charged ions form neutral atoms via gaining electrons. Gaining electrons is called reduction. Losing electrons is called oxidation. O xidation Is L oss R eduction Is
G ain Electrolysis of NaCl (l) Electrolysis of Sodium Chloride Solution The main ions present in sodium chloride solution are Na+ and Cl-, but there are also a few H+ and OH- ion present because water is very slightly ionised. The Na+ ions and H+ ions are attracted to the negative cathode. Here the H+ ions pick up electrons, since hydrogen is less reactive than sodium. The hydrogen ions gain electrons (reduction)to form hydrogen atoms, which then pair up to form hydrogen molecules. 2H+ + 2e- = H2 The Cl- ions are attracted to the positive anode. Here they lose electrons (oxidisation) to form chlorine atoms. These atoms pair up to form chlorine molecules. Chlorine gas is given off at the anode. 2Cl- = Cl2 + 2eThe products are hydrogen and chlorine, but Na+ and OH- ions are left in solution to make sodium hydroxide (NaOH) Uses of products: Chlorine: Purifying water, making PVC plastic. Hydrogen: Making margarine or ammonia. Purifying Copper The following ions are present in copper sulphate solution: Cu2+, SO42- (from CuSO4) H+, OH- (from water). The H+ ions and Cu2+ are attracted to the cathode but Cu gains electrons (reduction) more easily so that
copper is deposited Cu2+ + 2e- Cu At the anode, rather than the sulphate or hydroxide ions releasing their electrons, the atoms in the copper anode release their electrons (oxidisation) and form ions that then enter solution Cu Cu2+ + 2eTherefore, at the cathode, copper ions from solution are being deposited, and the cathode increases in mass. At the anode the copper atoms from the anode are going into solution as copper ions. The concentration of copper ions in solution remains unchanged. Other Uses of Electrolysis Reactive Metal Extraction Many of the more reactive metals (e.g. sodium, magnesium, calcium) can only be extracted from their ores by electrolysis. Electroplating Electroplating allows a thin layer of one metal to be deposited on another. e.g. Iron can be protected from rust by coating with chromium or nickel, or a cheap metal can be coated with silver or gold to make it look expensive. The object to be plated is placed as the cathode, while the metal to coat it is placed as the anode. The coating metal is also present in the solution. e.g. to nickel plate a piece of iron, the iron would be the cathode, the nickel would be the anode and the solution would be nickel sulphate. Electrolysis would cause Ni2+ ions in solution to be deposited on the iron cathode. Ni2+ + 2e- Ni These ions would then be replaced by Nickel metal slowly dissolving from the anode.
Ni Ni2+ + 2e- Extraction of Aluminium Aluminium is manufactured by the electrolysis of a molten mixture of aluminium oxide and cryolite. Cryolite is used to lower the melting point of aluminium oxide Graphite electrodes are used Aluminium forms at the negative electrode and oxygen at the positive electrode. The positive electrode is made of carbon, which reacts with the oxygen to produce carbon dioxide. CO2 Rates of Reactions The rate of reaction is how fast a reaction happens We can measure this by: the mass of a mixture, the volume of gas given off, measure the light transmitted. Important in chemical industry must make as much of a product as possible as cheaply as possible therefore to be made quickly Rate of reaction = amount of aneed reactant used
or amount of product formed and Time safely. Collision Theory Affected by the temperature, concentration, surface area, pressure and whether there is a catalyst. Reacting particles dont just bump into each other. They must collide with enough energy otherwise they will not react. Activation energy minimum energy needed for a chemical reaction to take place. Rates of Reactions Concentration Higher concentration = more collisions Dissolved particles are closer together therefore more collisions happen in an area of solution. Remember: increasing concentration or pressure does not increase the energy with which the particles collide. It does increase the frequency of the collisions, however. Surface Area Smaller pieces of materials have an increased surface area for a reaction to take place so quicker reaction time. Temperature At higher temperatures particles collide more often, which means that the energy transferred increases as the
particles move faster, moving faster means more collisions. At higher temperatures particles collide with more energy, and more energy means more energetic collisions. An increase of 10C roughly doubles the rate of a reaction. Rates of Reactions Catalysts Sometimes we need to change the rate of a reaction; we can speed up the rate of a reaction by adding a catalyst. A catalyst is something which increases the rate of a reaction but it is not affected chemically itself at the end of a reaction. Catalysts are not used up in the reaction so they can be used over and over again. Catalysts are often very expensive as they are made of precious metals. But, it is usually cheaper to pay for a catalyst for all the energy needed for the high temperature or high pressure. Some catalysts work by providing a surface for the reacting particles to come together. They lower the activation energy for the particles to react. Catalysts often come in the form of powders, pellets or fine gauzes, this provides the largest possible surface area for them to work. Endo- and Exo-thermic When a reaction takes place energy is involved, as energy is transferred as chemical bonds are broken and/or formed. Transferring energy from the reacting chemicals to the surroundings is called exothermic reactions. This means they heat up the surroundings, cause an
increase in temperature. Transferring energy from the surroundings to the reacting chemicals is called endothermic reactions. These mean they take in heat from surroundings, causing a decrease in temperature. Neutralisation between acids and alkalis is exothermic. Thermal decomposition and photosynthesis are endothermic. Acids and Alkalis Pure water is neutral on the pH scale When we dissolve a substance we make an aqueous substance The (aq) symbol shows that the ions are in an aqueous solution. This solution could be acidic, alkaline or neutral depending on what chemical has been dissolved. Bases can neutralise acids. Alkalis are bases which dissolve in water. (i.e. they are soluble bases) All acids form H+ ions when we add them to water it is the hydrogen which makes solutions acidic. Bases are the opposite of acids, in the way they react. All bases form hydroxide ions (OH-) when we add them to water. It is the hydroxide ions which make a solution alkaline Indicators change colour when we add them to a solution, we then use the pH scale to measure the acidity or alkaline (see above) A H+ ion is hydrogen which has lost an electron (proton) so we can call an acid a proton donor. Acids and Alkalis Some examples of acids, alkalis and neutral substances
Acid Sulphuric Acid Water Alkali Sodium Hydroxide Citric Acid Alcohol Potassium Hydroxide Hydrochloric Acid Nitric Acid Carbonic Acid Neutral Ammonia Making Salts From metal and acid We can make salts by reacting acids with metals This only works if the metal is above hydrogen in the reactivity series When the acid reacts with a more reactive metal, hydrogen gas is produced along with a salt. Metal + Acid
Salt + Hydrogen When we react an acid with a base we produce a From acid and bases solution which consists of a salt and water. This type of salt is soluble. Acid + Alkali Salt + Water When an acid reacts with an alkali neutralisation takes place During neutralisation H+ ions react with OH- ions to form water When we react acids and alkalis we need to know theyve completely reacted indicator paper, pH probe Making Salts From solutions precipitate reaction two We can sometimes make salts by combining solutions. This makes an insoluble salt, which is called a precipitation reaction because the insoluble solid is
called a precipitate. Silver nitrate and sodium chloride are both soluble. When you mix their solutions together, you make soluble sodium nitrate and insoluble silver chloride: silver nitrate + sodium chloride sodium nitrate + silver chloride AgNO3(aq) + NaCl(aq) NaNO3(aq) + AgCl(s) The silver chloride appears as tiny particles suspended in the reaction mixture - it forms a precipitate. The precipitate can be filtered, washed with water on the filter paper, and then dried in Man ethodoven. f 1. So or acid + in soluble me acid , b is mea ette ip p w a a li sured ase r med. alka sing
ded u + d in t a 2 d to a be u i . is c o The ba aker an d for a asured gh acid f se (or d Metho alkali is me , and enou he colour o c a li r tt b le o t e
ed 3. Th at a time un nate or meta 1. Th ator is add just change e soluti ti l) to indic on is fi l no more w is added a are urette ration) b d u e n il a lt s l r e e u dissolv m g r acted m ed li it in fro
e. ator (T cid and alka epeated us aterial, to remove ic e d v a in p r o any a and th rate, le the s of nt is e e e m a r. im v fi r lu ing the lt e vo expe dicato
pure s rate is left to 2. Th ed, and the s, but no in ave the salt a lt . le t e o m no e volu vaporated t m a s e e th tion is e solu Method for acid + insoluble base h T . 3 1. We find solutions which contain the two halves of the salt. 2. These solutions are mixed and form a precipitate, which can then be filtered off. 3. The precipitate is washed and dried e.g. to make silver chloride, we mix solutions of silver nitrate and sodium chloride.
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