First post, hello, I have a lot of questions.

[Jack777]

Hello, my name is Jack. I'm 65, live near Atlanta, and have never studied chemistry. I've been curious about chemistry but was never taught it in school as I went to a trade school. I have a ton of the most basic chemistry questions. 

Thanks.

[exchemist]

1 minute ago, Jack777 said:

Hello, my name is Jack. I'm 65, live near Atlanta, and have never studied chemistry. I've been curious about chemistry but was never taught it in school as I went to a trade school. I have a ton of the most basic chemistry questions. 

Thanks.

Welcome, and ask away! It may save time if you can read a bit on each issue, e.g. by scanning at least part of a Wikipedia article or something, first and then ask the questions about the parts you don't understand. (I say "part" because I realise these articles tend to plunge into a lot of detail, using possibly unfamiliar terms.)That way, people here don't have to recite a lot of stuff that is readily available on the internet. There are one or two other good sources  we can direct you to as well, if necessary. But we can see how it goes. 

[studiot]

Just now, Jack777 said:

Hello, my name is Jack. I'm 65, live near Atlanta, and have never studied chemistry. I've been curious about chemistry but was never taught it in school as I went to a trade school. I have a ton of the most basic chemistry questions. 

Thanks.

Yes welcome, here is some starter information that may be useful.

 

Originally Chemistry was divided into two categories  Organic Chemistry and Inorganic Chemistry.

The word organic meant that the 'chemicals' ( correct word substances )  derived from living things. Everything else was not organic or inorganic.

We now know that this distinction is not accurate but these two categories still remain although organic chemistry has been revised to the chemistry of carbon and its compounds.

So basically Chemistry is about all the varous types of substances and the interactions between both themselves and non material things such as light and magnetic fields.

Since those early days important sub classifications have been made such as

Analytical Chemistry  the Science of determining exactly which substances there are in a smaple and how much of each.

Physical Chemistry    The Science of the physical properties of substances such as density, colour, melting point, boiling point, refractive index, solubility etc

Structural Chemistry The study of the internal structure of each and every substance

Reachion Chemistry the study of rates and mechanisms if chemical reactions.

All of these apply to both Organic and Inorganic Chemistry.

 

Yet more subcategories apply to more specific areas such as biochemistry, mineralogy, crystal chemistry, rheology, molecular chemistry etc.

 

 

[Jack777]

3 hours ago, exchemist said:

Welcome, and ask away! It may save time if you can read a bit on each issue, e.g. by scanning at least part of a Wikipedia article or something, first and then ask the questions about the parts you don't understand. (I say "part" because I realise these articles tend to plunge into a lot of detail, using possibly unfamiliar terms.)That way, people here don't have to recite a lot of stuff that is readily available on the internet. There are one or two other good sources  we can direct you to as well, if necessary. But we can see how it goes. 

Thank you and much appreciated. 

Ok, I've been reading all the Apollo astronaut autobiographies and they mention the different fuels, for instance, hydrazine. Then it got me thinking about chemistry, I mean, how do they actually know it's hydrazine. I'm not really interested in the chemical composition of hydrazine, it just got me thinking.

I'm a complete and total neophyte to chemistry. I bought a periodic table of the elements clear plastic display from Amazon and it's fascinating.

Anyway, how do chemists actually know what a chemical really is? How can they look at a rock and say, ok, this rock has sulfur in it, or that rock has silver in it or whatever.

How do they know a pill has aspirin in it for example. How does anyone measure or test for these elements?

Who first discovered them? And I have read some articles but they assume a body of knowledge I don't have. I need something like a kindergarten level book. 

And the elements have a number like mg, 12. How do they actually know for certain it has what, 12 electrons?

This is the very basic stuff I'm talking about and I have even more dopey questions.

I spent my career in aviation but was never taught chemistry.

Take care. Jack.

[studiot]

Just now, Jack777 said:

I spent my career in aviation but was never taught chemistry.

Most traditional textbooks split upon the lines I have outlined.

They often go through a long list of chemical substances and their properties.
Although very systematic and thorough this can be rather boring for many.

 

However

If you were in the aviation industry you can probably cope with high school maths so this book might be an appropriate overview

 

Feel free to ask about anything you read that needs amplification or explanation.

Edited Thursday at 04:03 PM by studiot

[Jack777]

13 minutes ago, studiot said:

Most traditional textbooks split upon the lines I have outlined.

They often go through a long list of chemical substances and their properties.
Although very systematic and thorough this can be rather boring for many.

 

However

If you were in the aviation industry you can probably cope with high school maths so this book might be an appropriate overview

 

Feel free to ask about anything you read that needs amplification or explanation.

Thanks. I need something on the 1st grade level.

[exchemist]

3 hours ago, Jack777 said:

Thank you and much appreciated. 

Ok, I've been reading all the Apollo astronaut autobiographies and they mention the different fuels, for instance, hydrazine. Then it got me thinking about chemistry, I mean, how do they actually know it's hydrazine. I'm not really interested in the chemical composition of hydrazine, it just got me thinking.

I'm a complete and total neophyte to chemistry. I bought a periodic table of the elements clear plastic display from Amazon and it's fascinating.

Anyway, how do chemists actually know what a chemical really is? How can they look at a rock and say, ok, this rock has sulfur in it, or that rock has silver in it or whatever.

How do they know a pill has aspirin in it for example. How does anyone measure or test for these elements?

Who first discovered them? And I have read some articles but they assume a body of knowledge I don't have. I need something like a kindergarten level book. 

And the elements have a number like mg, 12. How do they actually know for certain it has what, 12 electrons?

This is the very basic stuff I'm talking about and I have even more dopey questions.

I spent my career in aviation but was never taught chemistry.

Take care. Jack.

OK, hydrazine. This is N₂H₄, https://en.wikipedia.org/wiki/Hydrazine  so made of molecules each of which has 2 atoms of nitrogen, joined by a single chemical bond N-N and with each nitrogen atom also being to joined by a bond to 2 hydrogen atoms. The astronauts and rocket scientists know what it is because it is made for them in a chemical plant, but if your question is how can someone , in principle, test this stuff to confirm its identity, then I think one would probably have a look at its infra-red spectrum. Molecules like this absorb infra red radiation at particular frequencies, according to the atoms present  and how they are bonded. (The bonds are stretchy, so if the atoms are pulled apart or pushed together, the bond can be set into vibration, the frequency of which depends on the mass at either end and the strength of the bond. Infra red waves of the exact frequency required can pull or push them in this way and when they do the molecule absorbs some of the  radiation, which the spectrometer can detect.)

But your more general question is really about analytical chemistry as a whole. This is a big subject. The various forms of spectroscopy, one of which I have described above, play a big role in helping to identify chemical compounds. But  there are also other methods which often involve trying to carry out chemical reactions to see what results. Normally this only works when you already have some idea of what you are looking for. 

I think your last question, about Mg and the significance of the number 12, actually gets us to an excellent starting point for some understanding of chemistry, because it gets us to the Periodic Table of the elements. Here's a link to one I use for reference: https://ptable.com/#Properties

Mg is the chemical symbol for magnesium and it is the 12th element in the table. 12 is its "atomic number". And you are right, the atom has 12 electrons, to balance the 12 positively charged protons in its nucleus. Chemistry is all about the electrons in the atom: electrons are what form chemical bonds. The number of electrons in atoms of the various elements determines how each element will behave, chemically. 

Mendele'ev, who originally designed the Table in the c.19th, did so without knowing this (!). He just observed there were similarities in the chemical behaviour of certain elements and grouped those into columns.  So for example, the column at far left with lithium, sodium etc. are all very reactive, soft metals which react with, say chlorine to form white salts with one atom of chlorine per atom of metal. (Common salt NaCl is one example.) The next group, with Mg, Ca etc in it, also form white salts but with two atoms of chlorine per metal atom. So he realised there is something important in common between Li and Na, and between Mg and Ca. The rest of the table was built up in similar fashion, from knowledge of the reactions of elements and the compounds they tended to form.

Nowadays we know it is to do with the way electrons build up in layers ("shells") like an onion, as one moves from lighter to successively heavier atoms, so that repeating patterns come back over and over when the shells are similar. This is something we can discuss. Elements with higher atomic number have more mass, so as one reads the table starting at the top left, one gets a progression of successively heavier atoms. The table is divided nowadays into blocks, according to the types of properties one finds in the columns (known as periodic table Groups). Again, this is something we can discuss. 

If you click on an element in the version of the table I have linked, you will get on the left a rather technical summary of key data but also, probably more interesting to you, a blue link to a Wiki text article all about the element.I suggest having a look at magnesium, since you asked about it, and perhaps also nitrogen, since you asked about hydrazine.

  

Edited Thursday at 07:40 PM by exchemist

[studiot]

1 hour ago, Jack777 said:

Thanks. I need something on the 1st grade level.

OK to start see my reply to this thread

Any questions on this ?

[Jack777]

6 hours ago, exchemist said:

OK, hydrazine. This is N₂H₄, https://en.wikipedia.org/wiki/Hydrazine  so made of molecules each of which has 2 atoms of nitrogen, joined by a single chemical bond N-N and with each nitrogen atom also being to joined by a bond to 2 hydrogen atoms. The astronauts and rocket scientists know what it is because it is made for them in a chemical plant, but if your question is how can someone , in principle, test this stuff to confirm its identity, then I think one would probably have a look at its infra-red spectrum. Molecules like this absorb infra red radiation at particular frequencies, according to the atoms present  and how they are bonded. (The bonds are stretchy, so if the atoms are pulled apart or pushed together, the bond can be set into vibration, the frequency of which depends on the mass at either end and the strength of the bond. Infra red waves of the exact frequency required can pull or push them in this way and when they do the molecule absorbs some of the  radiation, which the spectrometer can detect.)

Excellent explanation. Hydrazine was just the vehicle to trigger my curiosity about chemistry. What I need is much more fundamental. Like, how do they know which atom is which?

What is N-N? How do they even get nitrogen molecules? I like the idea of infrared. 

What is a chemical reaction? Is this like oil and vinegar? Is that a chemical reaction?

Thanks for the link, I have a clear plastic one similar to this I bought on Amazon.

Ok, another good explanation but how did he know he had chlorine?

How do they measure mass of an element? If we can't even see atoms or electrons how were they sure of this? See, these are the most basic questions I have about chemistry.

Anyway, this is all very interesting and I very much appreciate what you wrote.

Thanks.

Jack.

But your more general question is really about analytical chemistry as a whole. This is a big subject. The various forms of spectroscopy, one of which I have described above, play a big role in helping to identify chemical compounds. But  there are also other methods which often involve trying to carry out chemical reactions to see what results. Normally this only works when you already have some idea of what you are looking for. 

I think your last question, about Mg and the significance of the number 12, actually gets us to an excellent starting point for some understanding of chemistry, because it gets us to the Periodic Table of the elements. Here's a link to one I use for reference: https://ptable.com/#Properties

Mg is the chemical symbol for magnesium and it is the 12th element in the table. 12 is its "atomic number". And you are right, the atom has 12 electrons, to balance the 12 positively charged protons in its nucleus. Chemistry is all about the electrons in the atom: electrons are what form chemical bonds. The number of electrons in atoms of the various elements determines how each element will behave, chemically. 

Mendele'ev, who originally designed the Table in the c.19th, did so without knowing this (!). He just observed there were similarities in the chemical behaviour of certain elements and grouped those into columns.  So for example, the column at far left with lithium, sodium etc. are all very reactive, soft metals which react with, say chlorine to form white salts with one atom of chlorine per atom of metal. (Common salt NaCl is one example.) The next group, with Mg, Ca etc in it, also form white salts but with two atoms of chlorine per metal atom. So he realised there is something important in common between Li and Na, and between Mg and Ca. The rest of the table was built up in similar fashion, from knowledge of the reactions of elements and the compounds they tended to form.

Nowadays we know it is to do with the way electrons build up in layers ("shells") like an onion, as one moves from lighter to successively heavier atoms, so that repeating patterns come back over and over when the shells are similar. This is something we can discuss. Elements with higher atomic number have more mass, so as one reads the table starting at the top left, one gets a progression of successively heavier atoms. The table is divided nowadays into blocks, according to the types of properties one finds in the columns (known as periodic table Groups). Again, this is something we can discuss. 

If you click on an element in the version of the table I have linked, you will get on the left a rather technical summary of key data but also, probably more interesting to you, a blue link to a Wiki text article all about the element.I suggest having a look at magnesium, since you asked about it, and perhaps also nitrogen, since you asked about hydrazine.

  

 

2 hours ago, studiot said:

OK to start see my reply to this thread

Any questions on this ?

That was terrific! Many thanks.

6 hours ago, exchemist said:

OK, hydrazine. This is N₂H₄, https://en.wikipedia.org/wiki/Hydrazine

Gosh, I read this, light years over my head. I had no idea what they were talking about. All those letters with lines between them and all the names of other chemicals. I'm sure I'll understand this someday but for now it might as well be ancient Mesopotamian.  

Back in 1875 as they mentioned how did they identify what all the separate chemicals actually were?

I find this stuff interesting though.

[exchemist]

8 hours ago, Jack777 said:

 

 

Gosh, I read this, light years over my head. I had no idea what they were talking about. All those letters with lines between them and all the names of other chemicals. I'm sure I'll understand this someday but for now it might as well be ancient Mesopotamian.  

Back in 1875 as they mentioned how did they identify what all the separate chemicals actually were?

I find this stuff interesting though.

By 1875 they had a pretty good idea of how to characterise chemical compounds. Mendele'ev's periodic table came out in 1871. 

The basic way the c.19th chemists worked was by careful measurements of weight changes. They weighed the reactants and the products and from this were able, eventually, to work out the atomic weight of each element. Once they knew the atomic weights, they could use weight changes during reactions to establish the chemical formula for each substance.

It all started back in the time of Lavoiser, at the end of the c.18th (he lost his head in the French Revolution, in fact, poor fellow). He studied combustion, through which he  was able to find out things like the fact that when you burned something it absorbed only 20% of the volume of air available. So that told him there were 2 components in air, the 80% component being inert. He called it "azote", from the Greek for lifeless, which is French for nitrogen to this day. He also found the ash from burning phosphorus weighed more than the phosphorus before burning, and that this ash was acid when dissolved in water. So he realised the component of air that reacted had become part of the ash, along with the phosphorus - a chemical compound.  Because the ash was acid he called the reacting component of air "oxygene", from the Greek for acid-generating.  What he had made was phosphorus pentoxide P₂O₅, and when he dissolved it, he got a solution of phosphoric acid. 

(Lavoiser was subsequently shown to be wrong in associating oxygen with acidity, when hydrochloric acid was shown not to have any oxygen in it. In modern chemistry, acids are substances that release hydrogen ions, H⁺, in solution. So it was 2 steps forward, one step back.)   

It was by painstaking experiments like this, carefully weighting reactants and products, or carefully measuring volume changes in the case of gases, that by degrees the identities of chemical elements and compounds and their formulae came to be discovered, from the proportions in which they reacted.

 

[Jack777]

7 hours ago, exchemist said:

They weighed the reactants

Excellent explanation! Thanks.

Ok, so what is a reactant? 

And they weighed them? Were their scales that precise back then? And I still need to learn what atomic weight is. Phosphoric acid, how did he know it was phosphoric acid? Sorry for so many questions, I'm trying to learn and remember this stuff. Do you know of any good YT videos that explain this?

And what is an ion? How do they know it's an ion?

Anyway, these explanations are much appreciated. 

[TheVat]

I know this is more a memoir of growing up than a book about chemistry, but Oliver Sach's book, "Uncle Tungsten", does introduce the reader to chemistry in a way that conveys the fun and fascination.  And you pick up some concepts along the way, in a fairly painless way.   

Kate  Biberdorf's "It's Elemental," is also a good beginner's intro.  

[Jack777]

Just now, TheVat said:

I know this is more a memoir of growing up than a book about chemistry, but Oliver Sach's book, "Uncle Tungsten", does introduce the reader to chemistry in a way that conveys the fun and fascination.  And you pick up some concepts along the way, in a fairly painless way.   

Kate  Biberdorf's "It's Elemental," is also a good beginner's intro.  

Thank you kindly!

[exchemist]

1 hour ago, Jack777 said:

Excellent explanation! Thanks.

Ok, so what is a reactant? 

And they weighed them? Were their scales that precise back then? And I still need to learn what atomic weight is. Phosphoric acid, how did he know it was phosphoric acid? Sorry for so many questions, I'm trying to learn and remember this stuff. Do you know of any good YT videos that explain this?

And what is an ion? How do they know it's an ion?

Anyway, these explanations are much appreciated. 

I like these questions. When one is familiar with an area of science it is easy to ignore the original basis of the concepts one uses all the time. Some of these questions force me to go back and review the history of it all, which is informative. 🙂

OK, a reactant is something that takes part in a chemical reaction. For instance if you burn hydrogen, it reacts with oxygen and produces water: 2H₂ + O₂ -> 2H₂O. Hydrogen and oxygen molecules, shown on the left hand side of the chemical equation are the reactants and water, shown on the right, is the product of the reaction. So one quite commonly speaks of reactants and products.   

Yes good balances were available, as they were needed by gold and silversmiths for assay purposes. Joseph Black seems to have been the first to use one for chemical purposes at the end of the c.18th. He had one that was accurate to 0.1g, apparently.  So by the mid c.19th I expect they had them good for 0.01g or so, which is fine for the sort of thing they were doing.   

Re phosphoric acid, Lavoisier would obviously have known he had made an acid derived from phosphorus. But the modern term phosphoric acid probably would not have been applied to it until later.  

Regarding atomic weight, you will see that shown for each element on the periodic table, along with atomic number. It works like this: Atomic number denotes the number of protons in the nucleus. In a neutral atom this is the same as the number of electrons. When it comes to atomic weight,  electrons are so light their mass is negligible, at least in chemistry. What counts for atomic weight is the numbers of protons and neutrons in the atomic nucleus. Protons and neutrons weigh almost the same and the number of neutrons in a typical nucleus is normally about the same as the number of protons, though with some variation. So the atomic weight is generally about double the atomic number. Atomic weight is quoted in units of protons or neutrons. For example the atomic number of oxygen is 8. The atomic weight, on the table I linked to in my earlier post, is given as 15.999, so almost 16 but not quite. The reason why it is not exactly 16 is because although almost all oxygen atoms have 8 neutrons, a very small proportion have a different number. The number shown in the table is an average.

(These nuclei with different numbers of neutrons are different  "isotopes" of oxygen, from the Greek for "same place", i.e. they have different masses but occupy the same place in the periodic table. That is because, so long they all have 8 protons, and therefore 8 electrons, they have identical chemical behaviour - which is what defines them as the element "oxygen". )

This post is getting long, so I'll start a new one about ions.   

1 hour ago, Jack777 said:

Excellent explanation! Thanks.

Ok, so what is a reactant? 

And they weighed them? Were their scales that precise back then? And I still need to learn what atomic weight is. Phosphoric acid, how did he know it was phosphoric acid? Sorry for so many questions, I'm trying to learn and remember this stuff. Do you know of any good YT videos that explain this?

And what is an ion? How do they know it's an ion?

Anyway, these explanations are much appreciated. 

Right, ions. An ion is an atom in which the number of electrons is not the same as the number of protons in the nucleus. That means it will have a net electrical charge, +ve if it has fewer and -ve if it has more electrons than needed for electrical neutrality. I gave an example earlier with H⁺. This is a hydrogen atom with its one electron taken away, leaving just a proton. (If you've ever had an ulcer, you may have been prescribed a "proton pump inhibitor". This just means something that inhibits the mechanism in the stomach that secretes acid, so fewer protons, or hydrogen ions (H⁺) are produced.)

You can have ionic compounds: common salt is one. It consists of equal numbers of +ve sodium ions and -ve chloride ions, which attract one another and form a regular pattern in a crystal of salt. Both of these have lost or gained one electron per atom, but higher numbers are possible, depending on the element , e.g. Ca²⁺ or O²⁻ .  

One way you know you have got ions is if you dissolve the substance in water and see if it conducts electricity. Salt water conducts well, because +ve sodium (Na⁺) ions are attracted to the -ve wire  and chloride (Cl⁻) ions to the +ve one, so a current can flow.

(By the way the chemical symbol for sodium, slightly annoyingly, is Na, from the Latin natrium. The word originally comes from Wadi El Natrun in Egypt, where natural deposits of sodium carbonate are to be found. As Michael Caine would say, "Not many people know that".)   

Edited yesterday at 07:41 PM by exchemist

[studiot]

16 hours ago, Jack777 said:

That was terrific! Many thanks.

Glad you liked it.

So I would not start with atoms, molecules, electrons and protons, although you mqy have heard of some of them.

This is because we start with our encounter with the surrounding material world.

We create words and language to name and describe these things, rather as I have done with iron, wood, concrete. water etc.

Then with our scientific hat on we abstract properities, characteristics and abstract descriptions about these same things and how they might be similar or different.

We create an abstract model in our heads, computers or on paper.

So then we have two worlds a direct material one and an abstract one to deal with and this abstract one is where beginners especially find difficulty.

So I am going to suggest you re-read the list of sub caegories of chemistry I mentioned in my first post and we find a few examples in a preferable category to introduce the abstact science of chemistry and its specialist nomenclature.

You have already done this to some extent with your question

On 2/20/2025 at 3:45 PM, Jack777 said:

How do they know a pill has aspirin in it for example. How does anyone measure or test for these elements?

This is the way to keep the theory in touch with the tangible which makes for a more interesting subject experience.

So how about you pick one area and I will offer some examples ?

[Jack777]

18 hours ago, exchemist said:

Re phosphoric acid, Lavoisier would obviously have known he had made an acid derived from phosphorus. But the modern term phosphoric acid probably would not have been applied to it until later.

Thanks, and sorry for taking so long to reply as my wife broke her foot.

Ok, phosphorus, in order to actually know he had phosphorus he would have to burn it to look at the spectroscopic lines?

18 hours ago, exchemist said:

Protons and neutrons weigh almost the same and the number of neutrons in a typical nucleus is normally about the same as the number of protons

How can they weigh these or even see them?

18 hours ago, exchemist said:

Right, ions. An ion is an atom in which the number of electrons is not the same as the number of protons in the nucleus

 

18 hours ago, exchemist said:

You can have ionic compounds: common salt is one

But what I'd like to know is how are they sure about this? Is there a way to actually see this? Would I need to study physics for these answers?

18 hours ago, exchemist said:

One way you know you have got ions is if you dissolve the substance in water and see if it conducts electricity. Salt water conducts well, because +ve sodium (Na⁺) ions are attracted to the -ve wire  and chloride (Cl⁻) ions to the +ve one, so a current can flow.

Are there any videos of this? They can actually see the ions move?

Thanks for your help. I'm compiling a Pages document so I can read and reread to wrap my head around this stuff.

13 hours ago, studiot said:

So how about you pick one area and I will offer some examples ?

 

On 2/20/2025 at 10:42 AM, studiot said:

Analytical Chemistry  the Science of determining exactly which substances there are in a smaple and how much of each.

Yes. Analytical Chemistry is my main line of thought. This is precisely what I had in mind when I originally posted. Much appreciated.

[exchemist]

1 hour ago, Jack777 said:

Thanks, and sorry for taking so long to reply as my wife broke her foot.

Ok, phosphorus, in order to actually know he had phosphorus he would have to burn it to look at the spectroscopic lines?

How can they weigh these or even see them?

 

But what I'd like to know is how are they sure about this? Is there a way to actually see this? Would I need to study physics for these answers?

Are there any videos of this? They can actually see the ions move?

Thanks for your help. I'm compiling a Pages document so I can read and reread to wrap my head around this stuff.

 

Yes. Analytical Chemistry is my main line of thought. This is precisely what I had in mind when I originally posted. Much appreciated.

I’m going to break up the replies so we don’t get a lot of hares running in different directions.

First, Lavoisier didn’t have anything like spectrometer, back in the 1780s. He would have recognised phosphorus from its physical and chemical properties, as was done for all chemical substances before spectroscopy became an analytical tool, which was in the 1st half of the c.20th.

I’ll come back to the discovery of protons and neutrons later. But as to the question of weight of atoms, that comes down to weighing a sample of a substance and working out how many atoms are present in the sample. For that we need to introduce the concept of Avogadro’s Number, which is extremely important in chemistry and deserves its own post. So I’ll come back to that a bit later today, too.

[studiot]

Just now, Jack777 said:

Yes. Analytical Chemistry is my main line of thought. This is precisely what I had in mind when I originally posted. Much appreciated.

Ok so let us look further into analytical chemistry.

Say we have plenty of sample to play with.

We are normally interested in the answers to one or two questions or both.

The first question we ask is

What is in it or what is it made of ?

This is called qualitative analysis and is by far the easier of the two.

The second question is

How much ?

This is called quantitative analysis and I will come to that later.

 

So we can look at it and ask

Is it a solid, liquid or gas (at room temperature) ?

What colour is it ?   - Most substances are a white powder, colours are less usual and generally distinctive.

Will it dissolve in water, acid, benzene, or other common solvents ?
Geologists carry little bottles of acid which test rocks for the presence of calcium (eg limestone, chalk etc).

Lavousier may well have tried a flame test, although he would not have the modern advantages in this video from MIT.

Note in the video after the introduction the flame colours are shown with the overall flame colour on the left and the different colours making up the overall on the right.

 

[MigL]

I'm not a chemist but a physicist.
I last studied Chemistry in 76-77, my last year of high school, but I've been working as a 'chemist' for 38 years.
( see ? It's not that difficult )

Keep in mind that chemical reactions involve electron jumps, sharing and transfers.
They, in no way, alter the nucleus of the atoms involved; the number of protons and neutrons, and elemental atomic number stay the same.
That means all the reagents must be present in the products.

This gives clues for analyzing the products of a given reaction.
( and means there is no such thing as 'alchemy' )

Edited 3 hours ago by MigL

[studiot]

Just now, MigL said:

I'm not a chemist but a physicist.
I last studied Chemistry in 76-77, my last year of high school, but I've been working as a 'chemist' for 38 years.
( see ? It's not that difficult )

Keep in mind that chemical reactions involve electron jumps, sharing and transfers.
They, in no way, alter the nucleus of the atoms involved; the number of protons and neutrons, and elemental atomic number stay the same.
That means all the reagents must be present in the products.

This gives clues for analyzing the products of a given reaction.
( and means there is no such thing as 'alchemy' )

The flame test I referred to forms the beginnings of most modern spectroscopy, one of the main modern analytical tools.

Chemists have much to thank Physicists for in the development of the modern spectrometer. There are various sorts, Infra  red, Mass, Ultra violet, etc.
These are capable of answering the "How much ?" question and are often fully computerised and automated.

So there is a new term here, spectrum, which basically means a range of values.

Note also in the flame tests that the presented is using ions, which we will come to.

These are ions in solution (dissolved in a solvent) probably the most common way Chemists use ions.

Edited 2 hours ago by studiot

[exchemist]

3 hours ago, Jack777 said:

Thanks, and sorry for taking so long to reply as my wife broke her foot.

 

How can they weigh these or even see them?

 

But what I'd like to know is how are they sure about this? Is there a way to actually see this? Would I need to study physics for these answers?

Are there any videos of this? They can actually see the ions move?

Thanks for your help. I'm compiling a Pages document so I can read and reread to wrap my head around this stuff.

 

Yes. Analytical Chemistry is my main line of thought. This is precisely what I had in mind when I originally posted. Much appreciated.

OK, regarding weighing atoms - and thereby the protons and neutrons that make them up - this comes down to knowing what number of atoms there are in a given weight of substance.

Avogadro's number is the standard number used in chemistry. It defines what is called a "mole" of the substance. ("Mole" comes from German "Mol", which was a term derived from "molecule"). One mole of any substance contains 6.02 x 10²³ molecules of it (or atoms of it if it is an element). This extremely large number is Avogadro's Number.  The number is chosen such that the weight in grammes of one mole is equal to the atomic (or molecular) weight of the substance.  For example, one mole of carbon weighs 12g and contains  6.02 x 10²³ carbon atoms. (If you look it up you will see the atomic weight of carbon is 12.)  One mole of water contains  6.02 x 10²³ molecules and weighs (2 x 1 + 16) = 18g, because its formula is H₂O, and the atomic weight of H is 1 and that of O is 16.  

It is very important to know the number of moles of a substance when considering chemical reactions, because  that determines the proportions that will react together. For instance, taking water again, the formula H₂O means that 2 atoms of hydrogen are combined with one of oxygen in each water molecule. So in, say, the combustion of hydrogen, which produces water, 2 moles of hydrogen atoms will require one mole of oxygen atoms. In terms of weight, every 2g of hydrogen will take up 16g of oxygen. So when you do a lab reaction, you can weigh out the proportions you need and not have unreacted material left over at the end.

Coming back to protons and neutrons, In practice, nobody tries to express the mass of a proton or a neutron in grammes. But from the above I hope you can see we do have the relationship between the number of protons and neutrons in an atom and the weight of a set number of them in grammes, via the mole and Avogadro's Number.

There is a nice little write-up here of how Avogadro's Number came to be determined: https://www.scientificamerican.com/article/how-was-avogadros-number/  Admittedly it refers to a number of other pieces of physics and chemistry, but that's the way with science: everything is interlinked and feeds off other stuff. So to learn it there are times when you have to decide not to follow up all the loose ends at once, or you risk getting lost in a swamp of information.  

I'll come back to the question of ions separately, so that we can keep these strands of Q&A apart. 

2 hours ago, studiot said:

 

Lavousier may well have tried a flame test, although he would not have the modern advantages in this video from MIT.

 

Actually this is doubtful. A flame test requires a steady, non-luminous flame. This became available for the first time in the mid c.19th with the Bunsen burner. 

[Jack777]

4 hours ago, studiot said:

Note in the video

"Metal ions in the form of chloride salt solution with platinum wire." Now, I know I'm thick, I really am. How in the world did he know it was chloride and how did he know it was platinum? These are what I'd like to know. 

For example, the periodic table of elements in clear plastic I bought from Amazon has 103 elements in it. Supposedly. What I'd really love to know is whoever put this together had to buy the elements. So the person who provided him with the elements how does he know exactly what each element is? Did he use the flame method?

I'm getting there thanks to the video above and bought the books mentioned above.

5 hours ago, exchemist said:

He would have recognised phosphorus from its physical and chemical properties

This. How? Say I was walking in an area where it had a lot of rocks or wherever phosphorus comes from. How would I recognize it? I could stumble over it and wouldn't recognize it.