Atoms and equations
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Delivery guides are designed to represent a body of knowledge about teaching a particular topic and contain:
- Curriculum Content: A clear outline of the content covered by the delivery guide
- Thinking Conceptually: Expert guidance and activities on the key concepts involved, common difficulties learners may have, approaches to teaching that can help learners understand these concepts and how this topic links conceptually to other areas of the subject
- Thinking Contextually: A range of guidance and suggested teaching activities using a variety of themes so that different activities can be selected which best suit particular classes, learning styles or teaching approaches.
2.1.1 Atomic structure and isotopes
(a) isotopes as atoms of the same element with different numbers of neutrons and different masses
(b) atomic structure in terms of the numbers of protons, neutrons and electrons for atoms and ions, given the atomic number, mass number and any ionic charge
(c) explanation of the terms relative isotopic mass (mass compared with 1/12th mass of carbon-12) and relative atomic mass (weighted mean mass compared with 1/12th mass of carbon-12), based on the mass of a 12C atom, the standard for atomic masses
(d) use of mass spectrometry in:
(i) the determination of relative isotopic masses and relative abundances of the isotope,
(ii) calculation of the relative atomic mass of an element from the relative abundances of its isotopes
(e) use of the terms relative molecular mass, Mr, and relative formula mass and their calculation from relative atomic masses.
2.2.1 Electron structure
(a) the number of electrons that can fill the first four shells
(b) atomic orbitals, including:
(i) as a region around the nucleus that can hold up to two electrons, with opposite spins
(ii) the shapes of s- and p-orbitals
(iii) the number of orbitals making up s-, p- and d-sub-shells, and the number of electrons that can fill s-, p- and d-sub-shells
(c) filling of orbitals:
(i) for the first three shells and the 4s and 4p orbitals in order of increasing energy
(ii) for orbitals with the same energy, occupation singly before pairing
(d) deduction of the electron configurations of:
(i) atoms, given the atomic number, up to Z = 36
(ii) ions, given the atomic number and ionic charge, limited to s- and p-blocks up to Z = 36.
2.1.2 Compounds, formulae and equations
(a) the writing of formulae of ionic compounds from ionic charges, including:
(i) prediction of ionic charge from the position of an element in the periodic table
(ii) recall of the names and formulae for the following ions: NO32–, CO32–, SO42– , OH–, NH4+, Zn2+ and Ag+
(b) construction of balanced chemical equations, including state symbols, for reactions studied and for unfamiliar reactions given appropriate information.
(a) the periodic table as the arrangement of elements:
(i) by increasing atomic (proton) number
(ii) in periods showing repeating trends in physical and chemical properties (periodicity)
(iii) in groups having similar chemical properties
(i) the periodic trend in electron configurations across Periods 2 and 3 (see also 2.2.1 d)
(ii) classification of elements into s-, p- and d-blocks
(c) first ionisation energy (removal of 1 mol of electrons from 1 mol of gaseous atoms) and successive ionisation energy, and:
(i) explanation of the trend in first ionisation energies across Periods 2 and 3, and down a group, in terms of attraction, nuclear charge and atomic radius
(ii) prediction from successive ionisation energies of the number of electrons in each shell of an atom and the group of an element.
Approaches to teaching the content
When commencing an A Level Chemistry course students will arrive at the first lesson to hear that they will be studying, in the first few weeks, atomic structure, the periodic table and equations. They will feel some confidence in their understanding shortly before their legs are knocked out from underneath them and they are told that what they think they know isn’t the reality. This approach to the teaching of basic chemical concepts as half truths which support the passing of examination at GCSE level can lead to students having to unlearn their understanding when they reach the A Level classroom and can lead to a rocky start (and sometimes even failure), on an A Level Chemistry pathway.
This guide looks at ways of helping students to bridge the gap between the student or school made misconceptions of these ‘basic’ concepts which have been introduced at GCSE level.
The specification contains two main areas which are broached at GCSE and then developed at A Level:
- Compounds, Formulae and Equations
- The structure of the Periodic Table and its links to atomic structure (including electron structure).
The course will often commence with revisiting atomic structure and its links with Relative masses and the mole. However the activities suggested here commence with the humble equation and its importance to the understanding of what is happening within the chemical environment. This then allows the idea of formula to be introduced linking to atomic (and electron structure) before giving consideration to the structure of the periodic table.
Common misconceptions or difficulties students may have
Students may have varying degrees of confidence in dealing with balanced symbol equations and using them to recognise what is happening within a reaction.
They will have familiarity with the current view of the periodic structure and the link between properties and electron structure however they are unlikely to have given consideration to the idea that this is a ‘best fit’ model and like many other forms of classification may only deal with generalities e.g. misconception of Hydrogen as a typical atom.
Students may have a fixed view of the model of the atom failing to appreciate that it is the development of scientific understanding that has allowed us to reach this view and that continuing investigation such as that in CERN may lead us to further change our view.
Within this one model of the atom viewpoint students may also have developed school based misconceptions of the positioning of electrons within that structure based on the simplified model taught at GCSE this will include ideas such as the solar system perception of electron structure. This understanding of electron structure then pervades their view of chemical bonding favouring the ‘octet rule’ over ‘minimum energy’ explanations.
Useful further reading material:
Conceptual links to other areas of the specification – useful ways to approach this topic to set students up for topics later in the course
It is important that students are encouraged not only to learn new information relating to these concepts but to assimilate and apply it in appropriate contexts in order to overcome their retention of existing models from GCSE.
Balanced equations are fundamental to all chemistry and the ability to recognise the different types of reactions by identifying reactants and products will form the basis of most further study within the specification (e.g. Enthalpy calculations; atom economy). Understanding periodicity will make links to other aspects such as electronegativity whilst understanding atomic and more specifically electron structure will give the building blocks for the work on bonding and reactivity.
A range of activities about electronic configuration including:
- a simple PowerPoint which can be used to introduce the electron configurations
- a very straightforward electron configuration worksheet
- an online electron configuration video worksheet.
Using Alternative Science Theories (from Thinking Skills Through Science (12 Mar 2004) by Sue Duncan (Author), Don McNiven (Author), Chris Savory (Author) and David Leat (Author)).
Publisher: Chris Kington Publishing (12 Mar 2004)
Students are asked to consider how tenable alternative scientific theories are, providing evidence for or against the proposed theory.
Students could watch the Friends episode The One Where Heckles Dies in which Ross and Phoebe argue about evolution. This serves as a reminder that scientific ideas are constantly in development and that an open mind is required to study science.
The PPARC resource explores the historic development of the atomic model through to more recent developments in CERN.
To develop student understanding of the current structure of the Periodic Table and potential issues with its structure.
Students use the Gateway Contemporary Science issue lesson 12 property cards to develop their own periodic table and link properties to electron structure (as they currently understand it).
They then research key scientists involved in the development of the Periodic Table identifying their contribution to the development and present this to the group. (Students could be challenged to find an interesting way of conveying this information to students which may include recreating in model form some of the activities/investigations associated with these scientists).
Scientists to be included: Lavoisier; Newlands; Doberiener; Mendeleev; Rutherford; Seaborg
Students should then read Trouble in the Periodic Table by Eric Scerri and produce a critique of the current structure.
(Also useful is the Periodic Debate link).
These short worksheets can be used as a starter to test knowledge learned in a previous lesson, or alternatively can be used as a plenary activity.
The first two are on the history of atomic structure and isoelectronic species and can be used at either GCSE or AS Level.
Two PowerPoint files are of particular use – ‘Electronic Configurations’ and ‘Ionisation Energies’ (both found under the Physical Chemistry section).
The slides are designed for either classroom use or independent study and are extremely clear and comprehensive.
N.B. If you download the files directly from the website they will be saved as PowerPoint Show (.pps) files that cannot be edited. To edit the files, open them with PowerPoint and choose the ‘save as’ option to change to a .ppt file.
This activity is quite challenging and is designed to elucidate common student misconceptions and to prompt discussion. It is best to allow students to discuss the answers in small groups as this will make them challenge each other rather than simply guessing.
The answers provided with the worksheet include explanations and discussion points. In particular the resource challenges the ideas held by students about some atoms ‘wanting’ to lose electrons and also challenges their use of terminology when discussing the forces of attraction that exist within atoms.
At the beginning of AS Level, many students seriously underestimate the rate at which they need to assimilate new terminology into their scientific vocabulary.
This crossword is designed to be used at the end of the topic as a consolidation exercise. Once completed, students could be asked to make their own glossary or flashcards, choosing ten of the most important words.
Although not designed as an activity specifically directed at Gifted and Talented students, this activity is ideal for those students who find the work on electronic structure straightforward and do not require as much consolidation time.
The activity is very open ended and encourages students to examine how commonly used chemical words are defined and to identify any flaws or misleading terminology within these definitions. This is particularly useful for those students who excel at the more quantitative and ‘logical’ aspects of chemistry but who often fall down when it comes to producing written explanations.
This resource is designed to engage and challenge very able students and to inspire them by introducing the questions raised by cutting edge research into the behaviour of atomic ‘clusters’ or ‘superatoms’. The questions included in the article are subjective and challenge those students who may think that chemistry (when compared with biology and physics) is a rather ‘static’ science in which no real developments have been made in the last century.
The resource can be used as an individual or group activity, either in class or as a homework extension. An internet search of ‘superatoms’ will provide more related articles for particularly enthusiastic students.
This is a series of screencasts which will help to satisfy the curiosity of students who want deeper explanations for the principles of electronic orbital theory. In particular the sections on Quantisation of Energy Levels and The Shroedinger Atom provide more detail on the wave-particle duality of electrons and on the links between the observed evidence (atomic absorption and emission spectra) and the move towards a more quantum mechanical view of electrons in atoms.
Students should be encouraged to make notes as they watch the screencasts and identify areas that they want to research further, thus developing their ability to learn independently.
The premise of this guide is to develop students’ thinking skills through a range of individual and group activities involving Assessment for Learning.
Activities such as reproducing a diagram of a complex process can be a powerful aid to developing students’ understanding, problem solving skills can also be encouraged through collaborating in order to transmit information to the group. Specific activities are also identified to target Gifted and Talented (or the more able) students.
The first of these resources is a 14-16 AFL activity aimed at developing students’ understanding of the different types of chemical reaction. It is a useful starting point for eliciting students’ recall of common chemical reactions. This activity could be extended beyond the metal reactions on which it is based to include a wider variety of the six basic chemical reactions.
The second website gives information on these and has a quick quiz to check understanding.
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