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QUESTIONS: 2013; 1c The Periodic Table N 7 14 Nitrogen • The periodic table contains all of the known elements arranged in a specific way, according to their atomic structures • Each element is represented by a letter/letters corresponding to their name • Be aware that some letters do not correspond to the English name for that element (For example Pb is lead) • Each element will have two numbers written beside it. The smaller one corresponds to the atomic number whilst the larger one is the mass number. • Elements are arranged horizontally in ‘periods’. Each element in a specific period has the same number of electron shells • Elements are arranged vertically in ‘groups’. Each element in a specific group has the same number of electrons in its outer/valence shell © StudyTime 2015 Practice Question Use the position of Magnesium on the periodic table to justify how many electrons it has. Use this to explain the electron configuration of a Magnesium atom 12 24 d Mg v t Magnesium Magnesium is located three rows down and two columns across in the periodic table. This means that it is located in the third period and the second group. From this informa>on, we can tell that Magnesium has three electron shells, the last of which contains 2 electrons. We can assume that the first two electron shells are full with 2 electrons and 8 electrons. Adding these together, we get a total number of ( 2 + 8 + 2 = 12 electrons) and an electron configura>on of 2, 8, 2. This claim can be backed up by the atomic number of Magnesium, which is 12. © StudyTime 2015 QUESTIONS: 2014; 1b 2013; 1a • Atomic Structure All atoms consist of three types of subatomic particles. The relative numbers of these defines which element the atom is as well as its physical and chemical characteristics • Protons and Neutrons both exist in the dense central nucleus of the atom. Protons are positively charged whilst neutrons have no charge • Electrons circulate the outside of the nucleus and are negatively charged. They exist in shells/orbits which are constantly moving. • The outer electron shell of an atom defines most of its chemical properties. This shell is known as the ‘valence shell’ • The mass number of an atom tells us how many particles exist in the nucleus of an atom. It is therefore a sum of the number of protons and neutrons • The atomic number of an atom tells us how many protons there are in an atom • Atoms are neutrally charged and have equal numbers of protons and electrons © StudyTime 2015 Practice Question Describe the number of subatomic particles present in an atom of Carbon d 6 12 C v t Carbon Carbon has a mass number of 12. This means that there are 12 subatomic par>cles in the carbon nucleus. Carbon also has an atomic number of 6. This means it has 6 protons. Because the mass number is the sum of protons and neutrons, we know that Carbon has ( 12 – 6 = 6 neutrons). Because we are referring to an atom, we know that there is no overall charge. This means that there must be an equal number of protons and electrons present. Because of this, Carbon has 6 protons, 6 neutrons and 6 electrons. © StudyTime 2015 QUESTIONS: 2014; 1b 2013; 1a Electron Shells • Electrons are arranged in shells around the central nucleus. Each shell holds a maximum number of electrons • The outer electron shell of an atom defines most of its chemical properties. This shell is known as the ‘valence shell’ • The first shell is held very close to the central nucleus and can only hold two electrons • • The next two shells are much bigger and can hold 8 electrons each Electrons evenly arrange themselves in pairs across the shell. Repelling each other as they are all negatively charged. • The electron ‘arrangement’ or ‘configuration’ of an atom describes how many electrons it has in each shell. An example is Magnesium, which has the arrangement: 2, 8, 2. • The atom makes sure each electron shell is filled to its maximum before the next shell begins to be filled © StudyTime 2015 Practice Question For the following atoms, give the correct electron configuration Atom Atomic Number Electron Configura4on t Helium 2 2 Boron 5 2, 3 Oxygen 8 2, 6 Silicon 14 2, 8, 4 Phosphorus 15 2, 8, 5 © StudyTime 2015 Isotopes 7 14 N 7 15 Nitrogen • Isotopes are atoms of the same element with identical atomic numbers, but differing mass numbers • This means they have the same number of protons and electrons, but different numbers or neutrons N Nitrogen • Because neutrons have no charge and do not contribute to the chemical properties of an atom, different isotopes will behave the same in chemical reactions • Because neutrons contribute a small amount of mass to an atom, different isotopes of the same atom may have different physical properties (i.e boiling temperature) © StudyTime 2015 Practice Question Two isotopes of Carbon can be found in nature. Describe the similarities and differences between the two atoms. d 6 12 C v t Carbon 6 13 C Carbon Both atoms have the same atomic number. Because different elements are defined by their atomic number, we can say that both isotopes are the element Carbon. This means they have the same number of protons and electrons as each other and will hence behave the same in chemical reac>ons. However, Carbon-‐13 has one more neutron than Carbon-‐12. This means that Carbon-‐13 will have a slightly heavier atomic mass. Because of this, Carbon-‐13 may behave slightly differently in physical reac>ons such as mel>ng and boiling. © StudyTime 2015 QUESTIONS: 2013; 1b Ions Na + • While atoms on the periodic table have no charge, most of them are not stable • In order for an atom to be stable, it must have a full valence electron shell. In the case of atoms, this only covers the noble gases (last group of the periodic table) • Atoms can become ‘stable’ by losing or gaining electrons in order to have a full outer electron shell • Because they are losing/gaining negative electrons while maintaining the same amount of positive protons, they gain a positive or negative charge and are no longer neutral. An atom that is no longer neutral is called an ion. • Metals typically lose electrons to form positive ions, whilst non-metals tend to gain electrons to form negative ions © StudyTime 2015 Practice Question Describe the new electron configuration and charges on the following atoms Atom Atomic Number Atomic Electron Configura4on Ionic charge Ionic Electron Configura4on Helium 2 2 0 2 Boron 5 2, 3 3+ 2 Oxygen 8 2, 6 2-‐ 2, 8 Phosphorus 15 2, 8, 5 3-‐ 2, 8, 8 t © StudyTime 2015 Ionic Bonding Na + Cl + • -‐ In order for an atom to lose or gain electrons to form an ion, it must have a place to leave/gain the electrons from • Ionic bonds are a very strong form of bond as they involve the donation and acceptance of electrons • These places are found in other atoms through an ionic bond • • An ionic bond is a bond between a metal and a nonmetal, where the metal donates electrons and the non-metal picks them up Ionic compounds therefore have high melting and boiling points, and are unlikely to dissociate easily in water © StudyTime 2015 Practice Question Neither oxygen nor magnesium are stable atoms. However, they each form ions with different charges. Explain how this difference means they can form an ionic bond. 8 d O v t Oxygen 12 Mg Magnesium Neither Oxygen nor Magnesium have full valence electron shells. Because of this, they must each lose or gain electrons in order to become stable. Oxygen has 8 electrons and hence an electron arrangement of 2, 6. This means it has 6 electrons in its valence shell. It must hence gain 2 electrons to have an outer shell of 8 electrons. Magnesium has 12 electrons and an electron arrangement of 2, 8, 2. It must hence lose 2 electrons to have a full valence shell of 8 electrons. During an ionic bond, Magnesium donates these two electrons to Oxygen, sa>sfying both atoms and forming a strong bond. © StudyTime 2015 QUESTIONS: 2014; 1a, c Using an ion table +1 • • • Ion tables give the ionic charge formed on the ions of all of the atoms you will come across in your exam They are arranged in columns depending on the charges they form. All of the ions in each column originate as atoms from the same group of the periodic table. Ion tables refer to each ion by its chemical symbol, not by the name of the ion. This means you must be familiar with the symbol for each atom, as well as its name for the exam. • Ionic bonds must have an even number of electrons being donated an accepted. This means that an ion donating 2 electrons must interact with two ions accepting 1 electron. • The process of making sure the same amount of electrons are donated and accepted is known as balancing equations © StudyTime 2015 Practice Question How many Chloride ions will each of the following ions need to interact with to form an Ionic bond? (The Chloride ion has a charge of -1) Atom Atomic Number Atomic Electron Configura4on Ionic charge Number of Chloride ions Magnesium 12 2, 8, 2 2+ 2 Boron 5 2, 3 3+ 3 Beryllium 4 2, 2 2+ 2 Potassium 19 2, 8, 5 1+ 1 t © StudyTime 2015 QUESTIONS: 2014; 3c Acids H2SO4 • Acids are characterised by having excess Hydrogen atoms attached to them. These Hydrogen atoms are used to donate protons during chemical reactions. • Common acids you may come across include sulfuric acid, nitric acid and hydrochloric acid. • Acids have a pH of below 7. The lower the pH, the stronger the acid is. • Acids commonly react with bases to form a salt and water. • Acids can also react with metals to form a salt and hydrogen, and carbonates to form carbon dioxide, water and a salt © StudyTime 2015 Practice Question Write the products formed in the following acid reactions Acid Second Reactant Product(s) t Sulfuric Acid Zinc Zinc Sulfate, Hydrogen Nitric Acid Sodium Hydroxide Sodium Nitrate, Water Hydrochloric Acid Potassium Carbonate Carbon Dioxide, Water, Potassium Chloride © StudyTime 2015 QUESTIONS: 2014; 3a, b 2012; 3b, c Indicators 1 • There are two main indicators used in level 1 that tell how acidic a compound is • Litmus paper can tell whether a solution is acidic, basic or neutral but not how strong an acid or base it is • An acid will turn blue litmus paper red, whilst a base will turn red litmus paper blue 7 14 • Universal indicator can be used to tell roughly how acidic or basic a compound is • A few drops of universal indicator will turn a solution somewhere on the spectrum from red to blue/purple. The more red a solution is, the more acidic it is. The more blue a solution is, the more basic. • A solution that appears green when universal indicator is added is considered neutral © StudyTime 2015 Practice Question State whether the following observations correlate to an acidic, basic or neutral solution Observa4on Red litmus paper remained red, blue litmus paper turned red Conclusion t Acidic solu>on Red litmus paper remained red, blue litmus paper remained blue Neutral solu>on Universal indicator turned solu>on pink Weak acid Universal indicator turned solu>on dark purple Strong base © StudyTime 2015 QUESTIONS: 2013; 3b Collision Theory • Collision Theory describes the process of two or more molecules colliding together in order to make a chemical reaction proceed • In order for any chemical reaction to occur, these collisions must be happening • The more collisions there are happening per second, the faster the reaction will occur • Not all molecular collisions are successful. In order for a collision to contribute towards a chemical reaction, the molecules must hit each other at the correct orientation and must have the correct amount of energy • The minimum amount of energy required to make a successful collision occur is known as the ‘activation energy’ © StudyTime 2015 Practice Question Chemical reactions do not tend to continue for infinite periods of time – observations tend to level off once the reaction reaches a certain point. With reference to collision theory, explain why this is the case. d v In order for chemical reac>ons to occur, molecules must collide with each other at the correct orienta>on and with the minimum amount of necessary energy, known as the ‘ac>va>on energy’. Eventually, every reac>on will reach a point where all of the available molecules have performed collisions with each other. At this point, all of the reactants have been used up and hence no more product can be formed. Once the reac>on has ended, some collisions may occur. However, these collisions will not possess the ac>va>on energy required to help the reac>on proceed any further. © StudyTime 2015 QUESTIONS: 2014; 2a, b 2013; 2a Rates of Reaction Fast • • While all reactions require successful collisions in order to occur, there are a number of variables which dictate how many of these collisions happen. These variables give the rate of the reaction The concentration of the reactants effects the rate of reaction. This is because the higher the concentration of reactants, the more molecules are available to collide. This increases the likelihood of successful collisions occurring Slow • The temperature the reaction is occurring in effects the rate of reaction. This is because added heat gives the molecules more energy. This energy can be used to overcome the minimum activation energy barrier. • The surface area also has an effect on reaction rate. This is because the greater the surface area available, the more molecules are exposed to collide and the more successful collisions can occur • Catalysts can increase the rate of reaction by lowering the activation energy needed for collisions to be successful © StudyTime 2015 Practice Question Describe how the following changes to a system effect the colliding molecules, and use this to state how it effects the rate of reaction Change Effect on molecules Increase in temperature Molecules gain energy Occurs faster Decrease in concentra>on of one of the reactants Less molecules available to collide Occurs slower Catalyst added Molecules not directly effected. Ac>va>on energy required becomes less Occurs faster t Large chips of one reactant Increase in surface area broken into smaller pieces leaves more molecules exposed to collide Effect on reac4on rate Occurs faster © StudyTime 2015 QUESTIONS: 2014; 2c 2013; 4c 2012; 2c, 3a Balancing Equations 2NaCl + MgCO3 Na2CO3 + MgCl2 Coefficient Subscript • In order to gain full marks for any equation, you must make sure it is correctly balanced • Coefficients multiply the number of every atom in that compound by that value. • This includes making sure there are an even number of each atom on each side of the arrow • It is easiest to begin by balancing the Hydrogen and Oxygen atoms on each side of the arrow first • When balancing an equation, you are not allowed to change any of the subscript/small numbers written beside each individual atom. Instead, you must add coefficients to each compound • If you think an equation is correctly balanced, make sure to go back and double check each individual atom. Don’t be afraid to make a list of the atoms and keep a written track of how many appear on each side. © StudyTime 2015 Practice Question Balance the following equations: FeBr3 + H2SO4 d C4H6O3 + H2O Fe2(SO4)3 + HBr C2H4O2 Fe + Cl2 v FeCl3 2FeBr3 + 3H2SO4 Fe2(SO4)3 + 6HBr C4H6O3 + H2O 2C2H4O2 Fe +3 Cl2 2FeCl3 © StudyTime 2015 QUESTIONS: 2012; 2b Bases NaOH • Acids are characterised by having excess Hydroxide (OH-) groups attached to them. These hydroxide groups can be used to accept protons and form water (H2O) • Common bases you may come across often end with the word ‘hydroxide’, ‘oxide’ or ‘carbonate’ • Bases have a pH of above 7. The higher the pH, the stronger the base is. • Bases are able to ‘neutralise’ acids. This takes away their chemical properties and can make them a lot safer • Bases commonly react with acids to form a salt and water. • Bases that do not dissolve when placed in water are known as ‘Alkalis’. Most bases you will come across are akalis. © StudyTime 2015 Practice Question Hydrochloric acid is a very dangerous acid that can cause burns and corrode solids. Explain, using the equation below how a base can remove these dangerous properties. d OH-‐ + vH+ H2O The equa>on above describes the neutralisa>on reac>on between an acid and a base. During this reac>on, an acid such as Hydrochloric Acid dissociates to release a proton in the form of an H+ ion. As this is occurring, an added base such as NaOH is also dissocia>ng to form the OH-‐ compound ion. The OH-‐ ion acts as an ‘acceptor’ and is able to bond to the acidic H+ ion in the solu>on. The combina>on of these two ions forms water (H2O). As water is a neutral compound, it possesses no dangerous proper>es such as those present in Hydrochloric Acid. © StudyTime 2015 QUESTIONS: 2014; 2a Gas Tests + H or CO • • • All chemical reactions result in the formation of products from reactants. Sometimes, these products can be hard to identify as they have no distinctive color or texture • In order to run a test for Hydrogen, collect some of the unidentified gas in a test tube and trap with a bung or your finger. Hold a lit match over the test tube and release the bung. If you hear a ‘pop’ or ‘squeak’ sound, the gas created is Hydrogen • To test for carbon dioxide, bubble the unidentified gas through lime water. If the lime water turns a murky/cloudy colour, the gas is carbon dioxide. An example of this difficulty appears with distinguishing colorless gases from each other You may be tested on how to decide whether a gas produced is Hydrogen or Carbon Dioxide ? 2 © StudyTime 2015 Practice Question Part of an experiment in class requires you to react calcium carbonate with Hydrochloric acid. Write a method to determine the gas produced by this reaction, and explain what you would expect to observe d HCl+ CaCO3 ?? 1. 2. 3. 4. 5. Collect a small amount of the gas created by the reac>on in a clean test tube Immediately place a bung over the test tube Light a match over the test tube and quickly remove the bung If you hear a ‘pop’ or ‘squeak’ sound, iden>fy the gas produced as Hydrogen gas If no sound is heard, replace the bung with a tube and place the other end of the tube in a beaker of lime water 6. If the lime water turns murky/cloudy, iden>fy the gas produced as carbon dioxide As the reac>on involves a carbonate and an acid, I would expect to see carbon dioxide formed. This means that no ‘pop’ sound would be heard, but the limewater would turn cloudy © StudyTime 2015 Measuring Rates of Reactions Reaction Progress QUESTIONS: 2013; 3a, 4d 2012; 4a Time • • The rate of a reaction can be measured by tracking either the rate of product formation or the rate of loss of reactant. These measurements are made by taking readings of the product or reactant at regular intervals The rate of reaction can also be roughly measured by monitoring observations such as color changes. The faster these observations appear, the quicker the rate of reaction • The reaction progress is often graphed against time. The shape of this graph can give information on the rate of reaction • Reaction graphs tend to have a steep section where the reaction is occurring the fastest. This levels off and eventually reaches a plateau once all of the reactants have been used up • The steeper the initial section of the graph and the earlier the graph reaches its plateau, the greater the rate of reaction is © StudyTime 2015 Practice Question A reaction between calcium carbonate and hydrochloric acid is performed twice. Once with crushed calcium carbonate and once with large chunks. Use collision theory to decide which reaction used the crushed calcium carbonate. Reaction Progress d Reaction 1 Reaction 2 v Time Reac>on 1 was performed with the crushed calcium carbonate. This is because collision theory states that the greater the surface area available, the faster the reac>on will occur. This is due to the fact that the more surface area there is exposed, the more molecules are available to react to form products. As crushed calcium carbonate has more surface area, this reac>on will occur faster. In the graph above, reac>on 1 has a steeper gradient. It also reaches a plateau faster than reac>on 2. This indicates that reac>on 1 reaches comple>on first and is hence the faster reac>on. Reac>on 1 therefore involves the crushed calcium carbonate. © StudyTime 2015