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- Content: A clear outline of the content covered by the delivery guide;
- Thinking Conceptually: Expert guidance on the key concepts involved, common difficulties students may have, approaches to teaching that can help students understand these concepts and how this topic links conceptually to other areas of the subject;
- Thinking Contextually: A range of 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.
Mathematical learning outcome:
CM2.2i estimate size and scale of atoms
CM2.2ii represent three-dimensional shapes in two dimensions and vice versa when looking at chemical structures e.g. allotropes of carbon
CM2.2iii translate information between diagrammatic and numerical forms
Assessable content statements:
C2.2a describe metals and non-metals and explain the differences between them on the basis of their characteristic physical and chemical properties
C2.2b explain how the atomic structure of metals and non-metals relates to their position in the Periodic Table
C2.2c explain how the position of an element in the Periodic Table is related to the arrangement of electrons in its atoms and hence to its atomic number
C2.2d explain how the reactions of elements are related to the arrangement of electrons in their atoms and hence to their atomic number
C2.2e explain in terms of atomic number how Mendeleev’s arrangement was refined into the modern Periodic Table
C2.2f describe and compare the nature and arrangement of chemical bonds in:
i. ionic compounds
ii. simple molecules
iii. giant covalent structures
C2.2g explain chemical bonding in terms of electrostatic forces and the transfer or sharing of electrons
C2.2h construct dot and cross diagrams for simple covalent and binary ionic substances
C2.2i describe the limitations of particular representations and models
A hands-on experience with a number of metals and non-metals, recording their physical differences and testing for electrical conductance, is a good start to a general discussion of the more detailed difference in properties and reactions (see 'Properties of elements' activity). Metals predominate in the Periodic Table and all lie to the left hand side, with non-metals to the right.
Learners should understand that chemical reactions are all governed by the movement of the outer shell electrons, whether they are lost or gained completely forming an ionic bond, or shared forming a covalent bond.
Learners should be familiar with demonstrations of electrostatic attraction from Key Stage 3 Physics; the use of balloons is an easy means of showing such attractions as a reminder. This should then be discussed by looking at the number of attractions involved in making an ionic compound to get a real idea of the strength of the bond.
Learners may already have met the idea that hydrocarbons come with different carbon chain lengths. This visualisation is quite useful in a general discussion of small and polymer molecules with the chain link being the shared pair(s) while each atom is the oval part of the chain.
Giant covalent structures require a form of three dimensional modelling, such as Molymods, to make their arrangements clear. Learners will need to appreciate that we are trying to visualise something so small that we are unable to see it. As a result, there must be a hint of caution in accepting simple models such as the ones used here. Differences between elements involved in compounds mean that reality is far more complex .
Learners should realise that the early Periodic Tables were arranged by atomic mass, as this was all the information they had. However, realised that there were some anomalies when the elements were arranged in this way, and so he actually exchanged a number of elements even though the atomic mass seemingly put them in the wrong place. It was only when scientists discovered protons, neutrons and electrons that enabled Mendeleev’s table to be developed into the modern Periodic Table.
Common misconceptions or difficulties learners may have
There is a difficulty for learners in understanding what is happening at the atomic level; the great number of models needed to explain atoms and bonding makes this idea even harder. Learners may not realise that the nucleus remains unchanged in the bonding process. They may also think that a chemical bond is a physical thing like the stick in ball and stick model. Ion pairs, such as Na+ and Cl ‾, are often described as molecules. Learners also lack an appreciation of the 3D dimensions of compounds which, since this is an AS topic, may not be explicitly taught.
Conceptual links to other areas of the specification – useful ways to approach this topic to set learners up for topics later in the course
The material covered in this section is the basis of all understanding of chemistry. Though the ideas are not taken to their fullest extent, they need to be clearly understood as they underpin everything that is to come in the future study of chemistry. Elements react according to their need to gain the stable octet. How they react produces a huge range of new materials, all with differing properties due to the nature of the bonding involved. This is to be dealt with in the next section.
Approaches to teaching the content
An element can be identified by means of its combined Group and Period numbers (for example, Ca is in the position defined by being in Group 2 and Period 4). This in turn defines the element in terms of electron configuration as being in :
- Period 4 which means that there are four electron shells, the first three of which are full (2,8,8,2)
- Group 2 which means that there are two electrons in its outer shell.
This can then be taken to indicate the Atomic Number of the element, as this is the number of protonsmatching the number of electrons (in this case, 20).
A tray containing a number of metallic and non-metallic elements to be examined and their characteristics noted. All to be tested for electrical conductance.
This is a brief look at elements and their physical properties.
Inspect each element and write a physical description, test each element with supplied circuit and record whether or not they conduct electricity.
Try heating some of the materials provided under suitable conditions to compare melting points (Higher level). Research melting points of elements as seen in the tray and compare non-metal versus metals.
This is a useful online version of ionic jigsaws complete with feedback.
Follow the on-screen instructions to learn how to put the common ions together to form ionic compound formulae.
An activity that enables students to build upon the use of the Bohr model for atoms, ions and compounds.
The worksheets are downloadable prior to the lesson. Some preparation may be necessary beforehand but would be better done by the learners.
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