Tag: atoms

04-30 – Discovery of the electron

Today in chemistry history: J. J. Thomson and the discovery of the electron

04-30 – Discovery of the electron

On this day (30 April) in 1897, Joseph J Thomson announced the discovery of the electron. It was the first time a subatomic particle had been discovered. This graphic takes a quick look at his discovery; for a more detailed explanation, check out this Institute of Physics article. For more on different models of the atom over the years, there’s this graphic highlighting key theories and models.

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The History of the Atom – Theories and Models

An infographic history of the atom. Dalton identified that atoms of a particular element differ from those of other elements. Thomson discovered the electron and described the 'plum pudding' model of the atom: electrons scattered throughout a cloud of positive charge. Rutherford identified that the positive charge was concentrated in the nucleus of the atom. Bohr modified Rutherford's model by stating that electrons move in orbits of fixed sizes and energies. Schrödinger stated that electrons do not move in paths around the nucleus but in waves.
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All matter is made up of atoms. This is something we now take as a given and one of the things you learn right back at the beginning of high school or secondary school chemistry classes. Despite this, our ideas about what an atom is are surprisingly recent: as little as one hundred years ago, scientists were still debating what exactly an atom looked like. This graphic takes a look at the key models proposed for the atom, and how they changed over time.

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Mole Day – What is a mole in chemistry?

Infographic on the mole. One mole is the amount of substance that contains exactly 6.022 x 10^23 atoms, molecules or ions. This number is also known as Avogadro's number. Using moles makes it easier to talk about amounts of substances involved in reactions by relating the mass of a substance to its atomic or molecular mass. Amount of substance (moles) = mass (grams) divided by the mass of 1 mole (grams per mole). One mole contains a different mass for different substances.
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Today, 23rd October is Mole Day – which might put you in mind of small, furry, burrowing animals. However, they don’t even seem to have a commemorative day of any kind; we’re actually talking about the mole in chemistry, a concept that makes it easier to talk about the amounts of substances involved in chemical reactions. This is a fundamental concept and one that all chemists utilise.

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