how were the first atomic elements isolated and how did we know they could not be broken down further?
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Sir Humphrey Davy discovered 1/3 of all elements known in his time by using electrolysis, which a process which passes an electric current through a suitable solution.
The positive metal ions are attracted to the negative electrode, where they gain electrons and form metal atoms., while negative non-metal ions are attracted to the positive electrode, where they lose electrons and form non-metal atoms.
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He also invented the Davy lamp which saved thousands of lives in coal mines, but when asked about his greatest discovery he replied “My assistant, Michael Faraday”.
Late 18th and 19th century chemist discovered that the mass of a chemical reaction is always the same. The products (things that are left after) are equal to the reactants that you put in.
They also discovered that some compounds that can’t be broken down into other compounds, when reacted with other compounds that can’t be broken down into other compounds, produce things with predictable proportions. Water is always 8 parts oxygen and 2 parts hydrogen, Hemaitie is always 7 parts iron, 3 parts oxygen, ect.
This allowed elements to be isolated and identified and useful predictions to be made.
As to how they knew things could not be divided more; they’d figured out lots of ways to reduce compounds, and couldn’t find a way to break some of them them down more. Once you ‘crack’ water, you can’t chemically reduce the hydrogen gas, though it took a while to understand that ‘normal’ oxygen gas could be broken down to a different kind of oxygen gas.
Dalton only hypothesized the existence of atoms in 1804. Before that, no one knew about them (the Ancient Greek idea was slightly different.)
After Dalton figured out that they existed, it was just a matter of time before people were able to isolate them.
Although in 1661 Boyle proposed that some materials should be sort of base materials that cannot be further reduced, scientists didn’t always know which ones were such. Many elements were discovered at this time as “new substance”, so basically they knew they found a new thing but didn’t know whether this is an element.
How the materials were investigated at these times was like:
– reaction with acids and bases
– reaction with some known solutions, such as salt solutions (for precipitation)
– burning
– heating to high temperatures for decomposing.
Hydrogen was discovered as metals reacting with acids and the new kind of gas was then burned and turns out to burn into water.
Until 1789 when Lavoisier listed 33 materials as certainly elements, there was not a full list of things that were considered as elements. Out of the 33, some were not elements (he listed barium sulfate for example under the name baryte).
So as you see, what element is, wasn’t really clear at the time of their discovery, and scientists organized them much later.
A few elements are found in nature (they’re said to be native elements) – such as sulfur, silver, gold and mercury, but the modern definition is really quite recent. Even as late as 1789, Antoine Lavoisier, perhaps the greatest chemist of his time, only listed 33 – and 10 of those were wrong.
I believe that the earliest work involved breaking down of compounds into the elements, and identifying that a constant mass ratio (weight ratio) was seen in the products, and the reverse, that when reacting two different substances, the mass of reactants that were lost and the mass of the product also conformed to the mass ratio rules. Part of this work involved the production of “pure” materials which would not break down further.
Working with these observations led to the tabulation of elements by mass. Playing around with density relationships (mostly in gases) led to a refinement (correction) of the raw ratios to unit ratios. That is, when water was broken apart, you got 2 mass units of hydrogen (H) (which wasn’t called H at first) and 16 mass units of oxygen (O) (“phlogiston” in early work), but that 16 mass units would only give half the pressure that hydrogen (antiphlogiston) would in the same volume. This was taken to indicate that there was half as many “atoms” (the thing they decided must be the smallest unbreakable unit, just to have a marker, a base line, to work from; did not prove it at first, they assumed it) of oxygen as hydrogen in water.
So, this starts the thinking along the lines of what we now call “stoichiometry”, which is that elements combine in integer ratios that reflect the number of each “atom” in a specific compound.
Seeing that H was the “lightest” (least dense) “element”, they assigned that a mass value of 1, and worked up the scale from that.
And then the fun really started as they started to fill in the periodic table and noticed how certain patterns in chemical behavior arose in regular ways.
I tried to keep this short and simple, so it is not exact, just a rough summary.
The idea of the unit size of atoms only really came about once the atom model was combined with charge and electricity. That is, once the charge behavior of an atom was identified (like H would act like H+), and measurements of current used to quantities of product were correlated, the unit charge value and number of charged units was figured out (different experiments produced results that made lines, rough lines, when plotted in terms of mass and current, revealing unit charge from the slope, and unit charge leads to a way to calculate number of units per quantity of electricity. The size of the atom turned out to be extremely small.
By experimentation. People have always been trying to turn things into other things and coming across some things that they couldn’t break apart. Those things we’re determined to be “elements” until someone else found a way to break them.
The first good definition and method for determining something to be an element came from Antione-Laurent de Lavoisier, a French nobleman at the time of the Revolution. He formalized the theory of “conservation of mass” which states that matter (atoms) are not created or destroyed in chemical processes, they just recombine in different ways.
This theory meant there was now a method for evaluating if something was an element. You would weigh all the substances before and after a reaction. If a substance weighed less afterwards, it meant that it could not be an element. Some part of it had been broken away therefor it had been composed of multiple parts.
Lavoisier followed this method and tested everything he could get his hands on. He ended up producing the first modern list of elements, 33 in total including light and caloric, and discovered oxygen and several other gasses.
An example experiment to discover oxygen: When limestone (CaCO3) is heated in a furnace it produces quicklime (CaO). It was already known that this reaction also produced a gas, if you heat limestone in a sealed container it will inflate an attached bladder/balloon. This gas was called “fixed air” because it was air that was somehow originally attached to the limestone rock.
Lavoisier took this fixed air (CO2) and tested on a bunch of stuff. Some of the stuff he tested it one was burning phosphorus and burning wood. He found that these things would extinguish in the presence of “fixed air” and most importantly that the resultant substances would weigh exactly as much as the original substance PLUS the weight of the fixed air. He kept experimenting by adding fixed air to metals (calcination) to see if it combined and heating them to see if they produced their own types of air.
Others had done this sort of thing before, but what set Lavoisier apart was that he quantified and measured everything before and after which allowed him to track the movement of atoms across multiple reactions.
In practice, a lot of ‘stuff’ was discovered long before it was established that it were elements.
What do you mean by ‘atomic’ elements? Do molecules of a single element count? Metals? Carbon?
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