There could be problems for the public understanding of chemistry too. ‘When two experts in chemistry are discussing elements, they are able to distinguish the meaning from the context, but this is not so in the classroom,’ she says. Likewise if I say ‘Sulfur is the second element in group 16 of the periodic table.’ But these are two rather different things.Īccording to theoretical chemist Eugen Schwarz of the University of Siegen in Germany, the typical attitude is to say ‘I know how I speak about elements isn’t really correct, but everyone does it, and students will figure it out in the end.’ But ‘my personal feeling as a chemist is that one should not adopt this habit’, he adds.Įlena Ghibaudi of the University of Turin in Italy worries that this failure to define an element precisely raises problems of understanding, communication and trust in teaching. If I say ‘Sulfur is an element that forms a yellow solid with a pungent smell,’ I don’t expect objections. Some might say: who cares? We know what we mean in practice. We agree (right?) that hydrogen is an element – but what do we mean by that? Is molecular hydrogen gas an element? Or the isolated hydrogen atom? Or are we referring not to some actual substance but to a ‘transcendental’ notion of hydrogen of which actual atoms and molecules are just material representatives? The meaning of an ‘element’ is a favourite topic for argument among off-duty chemists. It seems reasonable to expect chemistry to provide an unambiguous definition ‘There’s a need for philosophical reflection on aspects of chemistry that we tend to teach in a rather mechanical way,’ says Eric Scerri of the University of California Los Angeles in the US, editor of the philosophy of science journal Foundations of Chemistry. It’s not just the definition of an element concepts such as molecules, bonds, and even the character of the periodic table itself, remain fuzzy: deceptively familiar from regular use by practitioners, but lacking any meaning that everyone agrees on. ‘Chemistry does not understand itself as a discipline,’ says philosopher Farzad Mahootian of New York University in the US. And some of the participants of the meeting implied that this might be for the best.įor others, it’s an indication that chemistry has some serious philosophical thinking to do. Some of chemistry’s finest minds, including Antoine Lavoisier, Mendeleev himself, and pioneer of nuclear chemistry Frederick Soddy, have grappled with it, yet still a concise and comprehensive definition remains elusive. The question was debated with much vigour and occasional passion during a meeting of the International Society for the Philosophy of Chemistry in Bristol in July 2018 – but still without producing any consensus. And yet no one can say quite what an element is. It’s one of the first ideas that the chemistry student encounters, often in the iconic tabulation of these basic ingredients of nature that Dmitri Mendeleev first described 150 years ago and which is being celebrated this year. Although most solutions we encounter are liquid, solutions can also be solid.As chemical concepts go, you don’t get much more fundamental than the element. The specific compositions of both of these solutions are not fixed, however, but depend on both source and location for example, the composition of tap water in Boise, Idaho, is not the same as the composition of tap water in Buffalo, New York. Thus air is a solution of nitrogen, oxygen, water vapor, carbon dioxide, and several other gases tap water is a solution of small amounts of several substances in water. Homogeneous mixtures are also called solutions. Examples of homogeneous mixtures are the air we breathe and the tap water we drink. If all portions of a material are in the same state, have no visible boundaries, and are uniform throughout, then the material is homogeneous. Air, tap water, milk, blue cheese, bread, and dirt are all mixtures. Very few samples of matter consist of pure substances instead, most are mixtures, which are combinations of two or more pure substances in variable proportions in which the individual substances retain their identity. Oxygen, for example, is a pure chemical substance that is a colorless, odorless gas at 25☌. Gases completely fill their containers, regardless of volume.Ī pure chemical substance is any matter that has a fixed chemical composition and characteristic properties. Liquids have a fixed volume but flow to assume the shape of their containers.
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