C CGP G CGP P H e a d S t a r Start your A-Level Chemistry t t o A Head Start to - L prep now with CGP! e v e l C h e m A-Level Chemistry i This superb book will help you get the best head start you can for A‑Level Chemistry... s t r y • Helpful recaps of key GCSE topics... Oh yes, we won’t let you forget anything! • New A-Level concepts clearly explained... Definitely, to nail those big ideas early on • Signature CGP study notes and practice questions... Of course — it is a CGP book after all! • And a free Online Edition included too... Read on your phone, tablet or PC (the sky’s the limit!) On your marks, get set... go smash A‑Level Chemistry with CGP’s Head Start Book! ☻ P.S. Don’t stop at Chemistry — we’ve got A‑Level Biology, Physics and Maths sorted too! Bridge the gap between GCSE and A-Level CGP Definitions: Ketone — Sound a piano makes ISBN 978 1 78294 280 1 9 781782 942801 CBR72 £4.95 (Retail Price) www.cgpbooks.co.uk CCGGPP CGP CCGGPP CGP books — they might CGP is the only choice just save your life... for A-Level Chemistry! OK, maybe not your life. But when it comes to exam revision, CGP are the undisputed champions. You can order any of our books (with next-day delivery!) from us, online or by phone: Unbeatable books, cards and practice papers for A-Level Chemistry www.cgpbooks.co.uk • 0800 1712 712 — revision essentials for AQA, Edexcel and OCR cgpbooks.co.uk Or you’ll find our range in any good bookshop, including: 0521 - 22634 Head Start to A-Level Chemistry When it’s time to start preparing for A-Level Chemistry, this CGP book will make sure you get off on the right foot (though the left foot is also a good option!). It’s the perfect mix of crucial things you’ll need from GCSE, and important new A-Level concepts. Of course, everything is explained with superb study notes and heaps of practice questions! CGP — still the best! J Our sole aim here at CGP is to produce the highest quality books — carefully written, immaculately presented and dangerously close to being funny. Then we work our socks off to get them out to you — at the cheapest possible prices. Contents Section 1 — The Structure of the Atom Atomic Structure ................................................................................................................................................1 Atomic Number, Mass Number and Isotopes .....................................................................................................2 Relative Atomic Mass ........................................................................................................................................3 Electronic Structure ...........................................................................................................................................4 The Periodic Table .............................................................................................................................................5 Section 2 — Formation of Ions Ionisation Energy ...............................................................................................................................................6 Formation of Ions...............................................................................................................................................7 Oxidation Numbers ...........................................................................................................................................8 Section 3 — Intermolecular Bonding Intermolecular Bonding .....................................................................................................................................9 Polarity ............................................................................................................................................................10 Section 4 — Bonding and Properties Ionic Bonding ..................................................................................................................................................11 Ionic Compounds ............................................................................................................................................12 Covalent Bonding ............................................................................................................................................13 Small Covalent Molecules ...............................................................................................................................14 Giant Covalent Structures ................................................................................................................................15 Metallic Bonding .............................................................................................................................................16 Trends in Properties Across the Periodic Table ..................................................................................................17 Section 5 — Chemical Equations Writing and Balancing Equations .....................................................................................................................18 Section 6 — Inorganic Chemistry Group 2 ...........................................................................................................................................................20 Group 7 ...........................................................................................................................................................21 Acids and Bases ...............................................................................................................................................22 Section 7 — Organic Chemistry Organic Molecules ..........................................................................................................................................23 Alkanes ...........................................................................................................................................................24 Alkenes ...........................................................................................................................................................25 Polymerisation .................................................................................................................................................26 Alcohols ..........................................................................................................................................................27 Section 8 — Chemical Reactions Reaction Types ................................................................................................................................................28 Section 9 — Rates of Reactions Reaction Rates .................................................................................................................................................31 Collision Theory ..............................................................................................................................................32 Reaction Rates and Catalysts ...........................................................................................................................33 Section 10 — Equilibria Reversible Reactions ........................................................................................................................................34 Le Chatelier’s Principle ....................................................................................................................................35 Equilibrium and Yield ......................................................................................................................................36 Section 11 — Calculations The Mole .........................................................................................................................................................37 Determination of Formulae from Experiments ..................................................................................................38 Calculation of Molecular Formulae..................................................................................................................39 Atom Economy ................................................................................................................................................40 Section 12 — Enthalpy Endothermic and Exothermic Reactions ...........................................................................................................41 Bond Energy ....................................................................................................................................................42 Section 13 — Investigating and Interpreting Planning Experiments ......................................................................................................................................43 Presenting and Interpreting Data ......................................................................................................................44 Conclusions and Error .....................................................................................................................................45 Answers ...........................................................................................................................................................46 Index ...............................................................................................................................................................51 The Periodic Table ...........................................................................................................................................52 Throughout the book, we’ve marked up content that you’re not likely to have come across at GCSE with stamps like this one. This is the CONNTEWEN T material you’ll be learning more about as part of A-Level Chemistry. Published by CGP Author: David Mason Editors: Emma Clayton, Mary Falkner, George Wright Typesetters: Callum Lamb, Kirsty Sweetman CBR72 ~ 0521 - 22634 With thanks to Karen Wells for the proofreading. With thanks to Emily Smith for the copyright research. Clipart from Corel® Illustrations by: Sandy Gardner Artist, email [email protected] Based on the classic CGP style created by Richard Parsons. Text, design, layout and original illustrations © Coordination Group Publications Ltd. (CGP) 2021 All rights reserved. 0800 1712 712 • www.cgpbooks.co.uk Section 1 — The Structure of the Atom 1 Atomic Structure Atoms contain Protons, Neutrons and Electrons 1) Atoms are made up of three types of subatomic particle: proton protons, neutrons and electrons. 2) In the centre of all atoms is a nucleus containing neutrons and protons. 3) Almost all of the mass of the atom is contained in the nucleus which has an overall positive charge. The positive charge arises because each of the protons in the nucleus have a +1 charge. 4) The neutrons in the nucleus have a very similar mass to the protons but they are uncharged. 5) Electrons are much smaller and lighter neutron than either the neutrons or protons. electron in a shell They have a negative charge (–1) and orbit the nucleus in shells (or energy levels). 6) There’s an attraction between the protons in the nucleus and the electrons in the shells. 7) The nucleus is tiny compared with the total volume occupied by the whole atom. 8) The volume occupied by the shells of the electrons determines the size of the atom. Here’s a round up of the properties of the subatomic particles: Particle Relative Mass Relative Charge Proton 1 +1 Neutron 1 0 1 Electron –1 2000 Atoms Have No Overall Charge The overall charge on an atom is zero. This is because each +1 charge from a proton in the nucleus is cancelled out by a –1 charge from an electron. If an atom loses or gains electrons it becomes charged. These charged particles are called ions. EXAMPLE How many electrons has an Al3+ ion lost or gained? The Al3+ ion has a charge of +3, so there must be 3 more protons than electrons. Ions are formed when electrons are lost or gained, so Al3+ must have lost 3 electrons. Neutrons are the perfect criminals — they never get charged... QPRUAECSTTIIOCNE S 1) Which subatomic particles are found in the nucleus? 2) What is the charge on an ion formed when an atom loses two electrons? 3) What is the charge on an ion formed when an atom gains two electrons? Section 1 — The Structure of the Atom 2 Atomic Number, Mass Number and Isotopes Atomic Number and Mass Number Describe an Atom 1) If you look at an element in the periodic table, you’ll see it’s given two numbers. These are the atomic number and the mass number. 2) The atomic number of an element is given the symbol Z. CONNTEWEN T mass numAberX 3) The atomic number is sometimes called the proton number element as it represents the number of protons in the nucleus of the element. Z symbol 4) For neutral atoms the number of protons equals the number of electrons, but you need to take care when considering ions as the number atomic number of electrons changes when an ion forms from an atom. 5) The mass number of an atom is given the symbol A. CONNTEWEN T 6) The mass number represents the total number of neutrons and protons in the nucleus. 7) Subtracting Z from A allows you to calculate the number of neutrons in the nucleus. EXAMPLE Use the periodic table to complete the following information about sodium. Element Symbol Z A No. Protons No. Neutrons No. Electrons Sodium 23 The periodic table tells you that the symbol for sodium is Na and Z is 11. The number of protons in sodium is the same as the atomic number, which is 11. You work out the number of neutrons by subtracting Z from A: 23 – 11 = 12. The number of electrons is the same as the number of protons, which is 11. Isotopes Have Different Numbers of Neutrons 1) Atoms of the same element always have the same number of protons, so they’ll always have the same atomic number, but their mass numbers can vary slightly. 2) Atoms of the same element with different mass numbers are called isotopes. 3) Isotopes have the same number of protons but different numbers of neutrons in their nuclei. EXAMPLE Copper has an atomic number of 29. Its two main isotopes have mass numbers of 63 and 65. How many neutrons does each of the isotopes have? The 63Cu isotope has 63 – 29 = 34 neutrons. The 65Cu isotope has 65 – 29 = 36 neutrons. Finding the number of neutrons — it’s as easy as knowing your A – Z... QPRUAECSTTIIOCNE S 1) Use the periodic table to work out how many neutrons are in a neutral phosphorus atom. 2) In terms of the numbers of subatomic particles, state two similarities and one difference between two isotopes of the same element. 3) Three neutral isotopes of carbon have mass numbers 12, 13 and 14. State the numbers of protons, neutrons and electrons in each. Section 1 — The Structure of the Atom 3 Relative Atomic Mass Calculating the Relative Atomic Mass 1) The average mass of an element is called its relative atomic mass, or A. r 2) When you look up the relative atomic mass of an element on a detailed copy of the periodic table, you’ll see that it isn’t always a whole number. This is because the value given is the average mass number of two or more isotopes. 3) The value of the relative atomic mass is further complicated by the fact that some isotopes are more abundant than others. It’s a weighted average of all the element’s different isotopes. 4) You can use the relative abundances and relative isotopic masses (the mass number of a single, specific isotope) of each isotope to work out the relative atomic mass of an element. 5) Relative abundances of isotopes are often given as percentages. To work out the relative atomic mass of an element, all you need to do is multiply each isotopic mass by its relative abundance, add all the values together and divide by 100. EXAMPLE What is the relative atomic mass of chlorine given that 75% of atoms have an atomic mass of 35 and 25% of atoms have an atomic mass of 37? Average mass = (abundance of 35Cl × 35 + abundance of 37Cl × 37) ÷ 100 = [(75 × 35) + (25 × 37)] ÷ 100 = (2625 + 925) ÷ 100 = 3550 ÷ 100 = 35.5 (You can check your answer against a periodic table to see if it’s right.) Calculating the Relative Formula Mass If you add up the relative atomic masses of all the atoms in a chemical formula, you get the relative formula mass, or M, of that compound. r (If the compound is molecular, you might hear the term relative molecular mass used instead, but it means pretty much the same.) CONNTEWEN T EXAMPLE Calculate the relative formula mass of CaCl . 2 Ca has an atomic mass of 40.1 and Cl has an atomic mass of 35.5. M = (1 × 40.1) + (2 × 35.5) r = 111 Together, my brother and I weigh 143 kg — it’s our relative mass... QPRUAECSTTIIOCNE S 1) Find the relative atomic mass of lithium if its composition is 8% 6Li and 92% 7Li. 2) Find the relative atomic mass of carbon if its composition is 99% 12C and 1% 13C. 3) Find the relative atomic mass of silver if its composition is 52% 107Ag and 48% 109Ag. 4) Find the relative formula mass of sodium fluoride, NaF. 5) Find the relative formula mass of chloromethane, CH Cl. 3 Section 1 — The Structure of the Atom 4 Electronic Structure Electrons are Arranged in Energy Shells 4th 1) Electrons orbit the nucleus in shells (also called energy levels). 3rd 2) You can draw concentric circles to represent the different shells. 2nd Then add crosses to represent the electrons at each level. 1st 3) For example, this diagram shows the energy levels, for an atom with 20 electrons, filling up with electrons. It has two electrons in the first shell, eight in the second shell, eight in the third shell and two in the fourth shell. (Remember you should always start filling the innermost levels first.) Here’s another way to show electron arrangements using simple notation: Hermit crabs: also arranged in shells. An atom with 6 electrons: 2, 4 The first number tells you how many electrons are in the first shell, the second An atom with 11 electrons: 2, 8, 1 number tells you how many electrons An atom with 20 electrons: 2, 8, 8, 2 are in the second shell, and so on. Energy Levels are Split into Subshells CONNTEWEN T Maximum Subshell electrons 1) Energy levels can be split into sub-levels called subshells. s 2 The first three subshells are called ‘s’, ‘p’ and ‘d’. They can each hold a different number of electrons. p 6 2) The first energy level has one subshell — an ‘s’ level. d 10 So the first energy level can contain up to 2 electrons. 3) At GCSE you learnt that the second energy level can contain up to 8 electrons. It’s actually split into 2 sub-levels. Two of the electrons are in an ’s’ level and the remaining six are in a ‘p’ level. If you combine the 2 ‘s’ electrons with the 6 ‘p’ electrons you get a total of 8. 4) Electrons generally start by filling the energy level with the lowest energy. So the first energy level will be completely filled before any electrons go into the second energy level. Within an energy level, electrons will fill the subshells in the order s, then p, then d. 5) As well as telling you how many electrons are in each shell, the electron configuration of an atom also tells you what subshells the electrons are in. For an atom with 10 electrons: 1s2 2s2 2p6 The little number tells The big number tells you how many electrons you the energy level. are in that subshell. The letter tells you the subshell. I’m trying to be calm, but my energy level is too high... QPRUAECSTTIIOCNE S 1) Draw diagrams to show the electron arrangements of the following elements: carbon, fluorine, magnesium, sulfur. 2) Use the simple notation shown above to write the electron arrangements of these elements: lithium, sodium, potassium, beryllium, magnesium, calcium. 3) Give the electron configurations of oxygen and chlorine. Section 1 — The Structure of the Atom