What is the definition of a compound? Why do atoms take part in chemical bonding?

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1 Page 1 What is the definition of a compound? Why do atoms take part in chemical bonding? When an atom loses an electron, what charge does the remaining ion have? When an atom gains an electron, what charge does the remaining ion have? What can we say about the electronic structure of ions? What do we call the elements in Group 1 When Group 1 metals react with non-metal elements, what type of ion is formed? What do we call the elements in Group 7? When Group 7 elements react with alkali metals, what charge does the halide ion gain? What type of structure is formed by ionic compounds? What type of bonding happens when atoms share pairs of electrons? What do we call covalent molecules with only a small number of atoms e.g. H2, Cl2, O2, HCl, H20, NH3 and CH4?

2 Page 2 Atoms take part in chemical bonding in order to achieve the electronic structure of a noble gas (full outer energy level). Compounds are substances in which atoms of two or more elements are chemically combined. When an atom gains an electron, the remaining ion has a negative charge. When an atom loses an electron, the remaining ion has a positive charge. Elements in Group 1 are called the Alkali metals. Ions have the electronic structure of a noble gas (Group 0). The elements in Group 7 are called the Halogens. When Group 1 metals react with non-metal elements, the Group 1 element forms an ion with a single positive charge. Ionic compounds form giant structures. When Group 7 elements react with alkali metals, the halide ion has a negative charge. Covalent molecules with only a small number of atoms are called simple molecules. When atoms share pairs of electrons, this is called covalent bonding.

3 Page 3 What can we say about the melting and boiling points of simple molecules? Why do simple molecules have low melting and boiling points? Why do simple molecules not conduct electricity? Why do ionic compounds have high melting and boiling points? Why do solid ionic compounds not conduct electricity? Why do ionic compounds conduct electricity when they are melted or dissolved in water? What type of molecules are diamond, graphite and silicon dioxide? Why do giant covalent structures have very high melting points? Damond and graphite are formed from which element? What is this molecule? What is this molecule? Why is diamond very hard?

4 Page 4 Simple molecules have low melting and boiling points as they have weak forces between the molecules. (HIGHER TIER) Simple molecules have low melting and boiling points? Ionic compounds have high melting and boiling points because there are strong electrostatic forces between oppositely charged ions. Simple molecules do not conduct electricity because the molecules do not have an overall electric charge. Ionic compounds can conduct electricity when melted or dissolved in water because now the ions are free to move. Solid ionic compounds cannot conduct electricity because the ions are not free to move. Giant covalent structures have very high melting points as all the atoms are linked to other atoms by strong covalent bonds. Diamond, graphite and silicon dioxide are giant covalent lattices (macromolecules). This molecule is diamond. Each carbon atom is forming four covalent bonds. Diamond and graphite are formed from the element carbon. Diamond is very hard because each carbon atom forms four covalent bonds. This molecule is graphite. Each carbon atom is forming three covalent bonds.

5 Page 5 Why is graphite soft and slippery? Why is graphite a good conductor of heat and electricity? (HIGHER TIER) What is the structure of fullerenes? (HIGHER TIER) Why are metals good conductors of heat and electricity? (HIGHER TIER) Why can metals be bent and shaped? What are alloys? Why are alloys harder than pure metals? What are shape memory alloys? What conditions can we change to alter the properties of a polymer? What is meant by a thermosoftening polymer? What is meant by a thermosetting polymer? In terms of intermolecular forces, why can thermosoftening polymers melt when heated? (HIGHER TIER)

6 Page 6 In graphite, one electron from each carbon atom is delocalised (free to move). These allow graphite to conduct heat and electricity. Graphite is soft and slippery because it consists of layers. There are no covalent bonds BETWEEN the layers so they are free to slide. Metals are good conductors of heat and electricity because they have delocalised electrons which can move. Fullerenes consist of hexagonal rings of carbon atoms. They have uses such as lubricants and in nanotubes. Alloys are usually made from two or more different metals (however a metal plus a nonmetal such as carbon would also be an alloy). Metals can be bent and shaped because the layers of atoms in metals are able to slide over each other. Shape memory alloys can return to their original shape after being deformed (eg dental braces). Alloys are harder than pure metals because the different sized atoms distort the layers so it is difficult for them to slide over each other. Thermosoftening polymers consist of individual tangled polymer chains. When we heat them, these polymers melt and can be reshaped. To alter the properties of a polymer, we can change the reaction temperature or use a different catalyst. Thermosoftening polymers have weak intermolecular forces between the chains. These are easily broken, so the polymer can melt easily. Thermosetting polymers consist of polymer chains with cross-links between them. They do not melt when they are heated.

7 Page 7 What is meant by nanoparticles? Why are nanoparticles useful? (a role may be described in the exam). What is shown by the atomic number of an element? What is shown by the mass number of an element? How do we calculate the number of neutrons in the nucleus of an atom? What do we call atoms of the same element with different numbers of neutrons? What is meant by the relative atomic mass (Ar) of an element? (HIGHER TIER) What is meant by the relative formula mass (Mr) of a compound? What is one mole of a substance? Elements and compounds can be detected and identified by instrumental methods. What does this mean and give an example. What are the advantages of analysing a substance using an instrumental method? How can we identify artificial colours in foods?

8 Page 8 Nanoparticles are useful because they have a high surface area to volume ratio. Nanoparticles are between 1-100nm in size (very small). They consist of a few hundred atoms. The mass number tells us the total number of protons and neutrons in the nucleus of an atom. The atomic number of an element tells us the number of protons in the nucleus of an atom. Atoms of the same element with different numbers of neutrons are called isotopes. To calculate the number of neutrons in the nucleus of an atom, subtract the atomic number from the mass number. The relative formula mass (Mr) of a compound is the sum of the relative atomic masses of the atoms in the numbers shown in the formula. The relative atomic mass (Ar) of an element is an average mass of the atoms of the isotopes compared with the 12 C isotope. An instrumental method involves using a machine. An example is gas chromatography. One mole of a substance is the relative formula mass in grams. Artificial colours in foods can be identified using paper chromatography. Instrumental methods are accurate, sensitive and rapid. They are useful when the amount of a sample of very small.

9 Page 9 Describe how gas chromatography works. How can we tell from a gas chromatograph how many different compounds are present? How can we work out the retention time from a gas chromatograph? How can we work out the relative molecular mass of a substance from a massspectrum? (HIGHER TIER) Suggest why the yield of a reaction is often less than the maximum calculated amount. How do we calculate the percentage yield for a reaction. What does this symbol mean? How can we calculate the rate of a reaction? What is meant by the activation energy? How does increasing the temperature of a reaction increase the rate of that reaction? How does increasing the pressure of reacting gases increase the rate of a reaction? How does increasing the concentration of reactants in solution increase the rate of reaction?

10 Page 10 The number of peaks on a gas chromatograph shows the number of compounds. In gas chromatography, different substances carried by gas, travel through a column packed with solid material. Each substance travel through the column at different speeds so they are separated. The rightmost peak on a mass spectrum is called the molecular ion peak. This tells us the relative molecular mass of the substance. The position of the peak indicates the retention time. percentage yield = (mass of product / theoretical maximum mass) x 100 The yield of a reaction is often less than the maximum calculated amount because some of the compound may be lost when it is separated from the reaction mixture There may be unexpected side-reactions The reaction may not go to completion because it is irreversible The rate of the reaction is calculated by either dividing the amount of product formed by the time taken. dividing the amount of reactant used by the time taken. This symbol shows that the reaction is reversible If we increase the temperature of a reaction, the particles collide more frequently and with more energy. This increases the rate of reaction. Activation energy is the minimum energy particles must collide with to react. Increasing the concentration of reactants in solution makes the particles collide more frequently which increases the rate of the reaction. Increasing the pressure of reacting gases makes the particles collide more frequently which increases the rate of the reaction.

11 Page 11 How does increasing the surface area of solid reactants increase the rate of reaction? What is the effect of a catalyst on a chemical reaction? How can using a catalyst save money when carrying out a chemical reaction? What is meant by an exothermic reaction? What is meant by an endothermic reaction? How can we use anhydrous copper sulfate to test for the presence of water? What are the state symbols for solid liquid gas dissolved in water Describe how we can make a soluble salt by reacting a metal with an acid. Describe how we can make a soluble salt by reacting an insoluble base with an acid. Describe how we can make a soluble salt by reacting an alkali with an acid. When we mix two solutions together and produce a solid, what name do we give to the solid? What is an alkali?

12 Page 12 Catalysts increase the rate of a chemical reaction. Increasing the surface area of solid reactants increases the frequency of collisions. This increases the rate of the reaction. An exothermic reaction releases energy to the surroundings. Generally exothermic reactions get hot. Catalysts increase the rate of a reaction so we can use a lower temperature and save energy costs. Anhydrous copper sulfate is copper sulphate without water. It is white. If we add water, we get hydrated copper sulfate which is blue. Hydrated means contains water. An endothermic reaction takes in energy from the surroundings. Generally endothermic reactions get cold. Add metal to the acid. Some metals are too unreactive (eg gold) and some metals are too reactive (eg group 1). The metal will effervesce (fizz) as the reaction releases hydrogen. When the metal stops reacting, all the acid has reacted. Now filter off the unreacted metal. Crystallise the salt produced by evaporation. Solid = s Liquid = l Gas = g Dissolved in water = aq Add the alkali to the acid until the ph is 7 (neutral). This can be determined using indicator paper. Now crystallise the salt produced by evaporation (note: you do not need to filter). Add the insoluble base to the acid. Keep adding until the insoluble base stops reacting (as the acid has all reacted). Now filter off the unreacted base. Crystallise the salt produced by evaporation. An alkali is a soluble metal hydroxide (eg sodium hydroxide). Alkalis have a ph value of A solid produced by mixing two solutions together is called a precipitate. This is a precipitation reaction.

13 Page 13 Suggest a ph value for an acid. What ph is a neutral solution? Which ion makes solutions acidic? Which ion makes solutions alkaline? What is the equation for neutralisation? Which salts are produced from: hydrochloric acid sulfuric acid nitric acid How is ammonium nitrate produced and what is it used for? What is meant by electrolysis? In electrolysis, what is meant by the electrolyte. During electrolysis, which ion moves to the negative electrode and why? Suggest a reason why we electroplate a metal with a different metal. During electrolysis, what takes place at the negative electrode?

14 Page 14 A neutral solution has a ph of 7. Acids have a ph between 1 and 6. The hydroxide ion (OH - ) makes solutions alkaline. The hydrogen ion (H + ) makes solutions acidic. hydrochloric acid = chloride sulfuric acid = sulfate nitric acid = nitrate The equation for neutralisation is H + (aq) + OH - (aq) H2O(aq) Passing an electric current through an ionic substance which is melted or dissolved in water, causing the substance to break down into elements. Ammonium nitrate is produced by reacting ammonia solution with nitric acid. Ammonium nitrate is used as a fertiliser. During electrolysis, the positive ion moves to the negative electrode. This is because opposite charges attract. In electrolysis, the electrolyte is the ionic compound which is broken down to its elements as electric current is passed. At the negative electrode, positive ions gain electrons. Gaining electrons is called reduction. Electroplating can be used to prevent corrosion. It can also be carried out to make a metal more attractive.

15 Page 15 During electrolysis, what takes place at the positive electrode? When electrolysing an ionic compound in solution, how do we work out what is produced at the negative electrode? Write the half equation for the oxidation of chloride at the positive electrode. (HIGHER TIER) What is the role of cryolite during electrolysis of molten aluminium oxide? During the electrolysis of molten aluminium oxide, what is produced at the negative electrode and what is produced at the positive electrode? During electrolysis of molten aluminium oxide, why does the positive electrode need to be replaced regularly? During electrolysis of sodium chloride solution, what is produced at the negative electrode? During electrolysis of sodium chloride solution, what is produced at the positive electrode? During electrolysis of sodium chloride, what solution remains at the end?

16 Page 16 If the metal is more reactive than hydrogen, then hydrogen is produced at the negative electrode. If the metal is less reactive than hydrogen, the metal is produced at the negative electrode. At the positive electrode, negative ions lose electrons. Losing electrons is called oxidation. Cryolite lowers the melting point which reduces the energy needed, saving money. 2Cl - Cl2 + 2e - or 2Cl - - 2e - Cl2 During electrolysis of molten aluminium oxide, graphite electrodes are used. Oxygen is produced at the positive electrode. The oxygen reacts with the carbon graphite, producing carbon dioxide. The positive electrode therefore needs replacing regularly. During electrolysis of aluminium oxide, aluminium is produced at the negative electrode and oxygen is produced at the positive electrode. During electrolysis of sodium chloride solution, chlorine gas is produced at the positive electrode. This is used to make bleach and plastic. During electrolysis of sodium chloride solution, hydrogen gas is produced at the negative electrode. During electrolysis of sodium chloride solution, sodium hydroxide solution remains at the end. This is used to make soap.