AS and a Level Geology Learner Resource 2 Global Tectonics

Learner resource 2–Goldschmidt Classification of the Elements

Introduction

Victor Goldschmidt was a Swiss Norwegian whose research in the early twentieth century covered both physical chemistry and geology. Chemists know him for his work on the lanthanide elements and geologists for the Goldschmidt classification of the elements. Goldschmidt classification is empirical which means that it is based on experiments he carried out on the residues from smelting copper sulfide ores and the composition of meteorites. He observed the same associations of elements into four groups in both meteorites and smelting products. Goldschmidt classification gives us principles that help geologists understand the distribution of elements in the Earth.

Activity

The foundation in Chemistry learners have gained from their studies at GCSE is developed and entwined through many aspects of the Geology course. Most significant sections which depend on prior chemical studies include 2.1.1 Minerals where learners are required to express compositions of minerals using chemical formula and when considering the crystalline structures of rock - forming silicate minerals. This thread continues into 3.1.1 Theorigin of the Earths structure where learners will be able to apply and develop their understanding of the trends and patterns in chemical behaviour by introducing the Goldschmidt classification of elements. In module 5.3.1 Igneous Petrology learners can build on their understanding of particle theory in particular what happens during changes of state, these skills will help learners understand the processes represented by phase diagrams. A final strong thread learners can develop is their understanding of redox reaction which is developed through module 5.5.1 Sedimentary processes and resources where learners consider the occurrence of banded iron formations in the Paleoproterozoic produced in a differing chemical environment to the present day. Other areas which have strong roots in chemical understanding are diagenesis, metamorphism, contaminated soils and clays and isotope geochemistry.

The aim of the lesson element is to maintain and refresh learners chemical knowledge and understanding using the context of the A level Geology course. Not only will this help their understanding at this level but by continuing to use and apply the fundamental concepts of chemistry they will feel more confident and prepared when studying a range of Earth Science degree courses in their future career paths. The most relevant parts of the GCSE chemistry course that learners come with an understanding of include atomic structure and the periodic table, changing state and chemical bonding, the chemistry of carbon based structure, redox reactions, separating chemical mixtures and the reactivity series.

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Global Tectonics

Learners are aware of how to calculate the number of sub atomic particles of an atom from atomic number and mass number and can link this information to their position on the periodic table. Using the elements location on the periodic table learners are able to make predictions on how the element will behave chemically and physically. Although they understand the make-up of the periodic table they often don’t make as much use of it as a resource when asked to predict patterns and behaviour as they could, relying on trying to memorise the chemical behaviour of many elements. From studying GCSE Chemistry learners understand how the type of bonding in a chemical species relates to its physical properties. They are aware that giant covalent structures have high melting points and can be very hard, whilst simple molecular structures have low boiling points and that it is the intermolecular forces that are significant. Learners understand that metals and non-metals bond using ionic bonding arranged in giant ionic structures which explains their high melting points and crystalline structure.

The origin of the Earths structure 3.1.1d and 3.1.1e (Goldschmidt classification and relationship to differentiation of the earth into layers of distinct composition makes use of skills learners have from their knowledge and understanding of the periodic table of elements. An elements position in the periodic table indicates the type of bonding it will form. This feature will also determine the Goldschmidt group that the element is assigned to.

Before providing any new information on Goldschmidt learners can be given the keywords associated with the topic. They should use four different coloured pens/pencils to make connections between terms that are related and if possible annotate the links to explain their decisions. Words to include shown in table below, they are grouped into four columns and include new words used by Goldschmidt and words learners are already able to use. Words need to be randomly arranged when given to learners with plenty of space between them to allow arrows and labels to be drawn.

Atmophile / Lithophile / Chalcophile / Siderophile
Atmosphere / Crust / Mantle / Core
Gas Phase / Oxides / Sulfides / Metallic bonding
Noble gases / Halogens / Copper / Transition Metals
Simple molecules / Alkali metals / Zinc / Iron
Hydrogen / Alkaline Earth metals / Transition metals / Nickel
Helium / Ionic bonding
Silicates
Sodium
Chlorine

The grouping of the keywords will be reviewed as a plenary.

Following this introduction learners need to be provided with a copy of the periodic table of elements. Within the classroom four stations should be set up, each providing information about one of Goldschmidts groups. The chemeurope.com site provides well written information about each groups, the information is well differentiated to provide some stretch and challenge and challenging language but also some basic content. The list of elements within each group would need to be removed from the beginning of the section.

Learners visit each of the four areas with their periodic table and use the information to decide which elements fall into each category and then colour their periodic table in the four colours to match.
After completing this learners can self-assess their periodic table with one showing the Goldschmidt classification, for example select 10 features to check against.
Now learners can use their annotated periodic table to predict the likely type of bonding found in each of the four groups using their existing knowledge of the behaviour of chemicals, for example noble gases, simple covalent or transition metals, metallic bonding and therefore predict physical properties.

Finally they can return to their keyword scramble and make adjustments in light of what they have found out about Goldschmidts groupings, the answers could be displayed for them to check against, allowing time to discuss evaluate differences. For example compare with the Geologist’s Underground Map of the Elements, are there elements which could be assigned to more than one grouping.

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Global Tectonics

Goldschmidt Classification of the Elements

Group the words overleaf into four categories using a different colour for each Goldschmidt category.Annotate arrows to explain your decisions.
Take the blank periodic table provided and visit the four information points.Choose one colour for each group, assign chemical elements to each of the four Goldschmidt categories.
Self-assess your annotated periodic table, make a note of any major differences and suggest why this may have occurred.
Consider the four Goldschmidt categories and their distribution in the periodic table and using what you know about chemical bonding suggest the type of bonding each of the groups will demonstrate.Use your suggestions to predict physical and chemical properties which will arise due to the type of bonding.
Return to the keyword scramble to review your earlier grouping, make any improvements or additions based on what you have found out about the Goldschmidt classification.

Global Tectonics