If you want to discuss the philosophical concept of ‘substance’ then by all means do, but in its current form that is definitely a question for a chemistry forum.

The first definition is the only one you need to worry about as it is the scientific definition...

"Element" in the sense of "a macroscopic substance made up of one type of atom", is merely a colloquial (informal) way to use the word that is a vestige of chemistry's primitive origins.

Prior to the discovery of the atom, (al)chemists had all kinds of ideas about what substances were, and many sought to identify what they thought were the basic ingredients of matter. By attempting to identify basic substances, their properties, behavior, and what happens when they are combined under different conditions, they hoped to gain understanding and control over them.

This sense of the world "element" or "elemental" has a connotation of basic ingredient.

Ok so elements are species of atoms right? So why do we call an aggregation of sodium atoms - sodium?

Same reason we call a flock of sheep sheep. It's just the way we happen talk.

My understanding of chemistry notation is that an element can be a substance made up of just one type of atom such as hydrogen gas, pure gold and graphite are elements. Whereas substances made up of more than one type of atom such as water, salts, bronze and carbon dioxide are not.

Hey there seagull appreciate the response! So what do you mean by a “substance” though. I often see it being defined as a form of matter having constant chemical composition with characteristic properties although I do not understand what this means. If you could clarify the meaning of “substance” in the context of chemistry that would be great. Thanks in advance.

Some scientists and teachers use words in inconsistent ways so don't assume every sentence they say is necessarily true because then you end up in confusion, but if you get confused it means you notice an apparent inconsistency so it's good to have it resolved. Probably different people in chemistry will use the word substance in different ways. To me a substance may be a liquid, a gas, a solid.

So the definition "substances made up of one type of atom" would mean a liquid, gas or solid made up of one type of atom. But a liquid, gas or solid is not necessarily made of just one type of atom, so then water could be characterized as a substance but not as made of just one type of atom.

If you define substance as a "form of matter having constant chemical composition with characteristic properties", then for instance water in a glass is a substance, but if you pour syrup into it it's not the same substance anymore it becomes another substance with a different chemical composition (different atoms or molecules) and different properties (different color, different density, different electrical conductivity, ...)

Salt water is a mixture not a chemical substance (by strict definition). A solution is always a mixture.

Once you evaporate off the water and you have H20 and Na, they are separate chemical substances.

Since nothing is really pure though (unless achieved by chemistry) we dismiss negligible impurities to call something a substance.

Table salt has trace minerals in it and is hydrophilic, so while according to theory it is a chemical substance insofar it ought only contain NaCl, it is practically always a mixture of trace minerals, salt and water and atmospheric gas.

A chemical substance is either a homogenous aggregation of molecules or elements. A substance can only contain one type of molecule or element (discounting isotopes maybe), otherwise it is a mixture.

I hope this hasn't confused you more.

I often see it being defined as a form of matter having constant chemical composition with characteristic properties although I do not understand what this means — blokeybloke

There are several properties one could measure. One such oft-used property is the melting point or the boiling point of a substance, which is just the temperature required to make some sample to change phases at standard pressure.

Salt water does not contain either a uniform composition or a stable boiling point. You'll have a different number of sodium and chloride atoms to water atoms, depending on the sample, and that ratio will change the boiling point.

But salt, by itself, and water, by itself, *does* have a set boiling point. Water, at standard pressure, will boil at 100 degrees Celsius. Where the salt water will boil at different temperatures depending on the ratio between salt and water.

I don't think "substance" has a precise technical meaning in the context of chemistry. You could differentiate this mixture of salt and water from, say, just salt by itself and water by itself and say these are substances whereas mixtures are not -- thereby setting out how you mean to use the word "substance" in the conversation. But you could also say it more plainly and say that salt-water and salt and water are all substances too. What is important is to lay out what you mean in the event of confusion between two possible uses of the word. In the latter case, where "substance" is not being used to differentiate between mixtures and samples with fixed properties, usually all that is meant is something like "an inert something or other" -- something material, whatever it might be. It's a very general word.

I don't think "substance" has a precise technical meaning in the context of chemistry. You could differentiate this mixture of salt and water from, say, just salt by itself and water by itself and say these are substances whereas mixtures are not -- thereby setting out how you mean to use the word "substance" in the conversation. — Moliere

It does have a precise meaning in the context of chemistry but it probably isn't of much use really.

Guys I might be having trouble with language or overthinking things but is water a type of molecule or is water made of molecules? In other words what do you guys think of when you think of water? A type of molecule or the liquid that you drink? I feel so stupid for asking a question like this but if someone could answer me I would be thankful.

Also why do people call H2O a liquid?? I thought H2O was a type of molecule so how can a molecule be a liquid?

Sounds like you just need to go study your chemistry text, or troll a chemistry forum.

Is water a type of molecule or is water made of molecules? — blokeybloke

Both. Water is composed of molecules, each of which are molecules of water. This isn't so much a question of philosophy or chemistry than an ambiguity in how language is used. Water is simply an equivocal term, which is used differently in different contexts.

Consider the word "star". Does it refer to a star you see in the night sky, does it refer to a star you have drawn on a piece of paper, or does it refer to the Sun which itself is a star? The answer is all of them, the same word can refer to one thing or another depending on the context.

Words are an imperfect tool to communicate, you won't ever find a perfect definition of anything, each word is defined in terms of other words which themselves are defined in terms of other words and so on and so forth, so fundamentally each word is defined circularly in terms of itself and you will never find an answer by looking only at definitions. How a word acquires meaning is through how you see it used. The word water is used differently in different contexts, sometimes people are talking about the liquid (or solid or gas) that they see as a whole, sometimes they are talking about an individual molecule that makes up the liquid (or solid or gas).

H2O is a molecule, a bunch of H2O molecules interacting with each other can be a liquid, but a molecule itself isn't a liquid, so if someone says "the liquid H2O" they are using the word H2O improperly, using it as a shorthand for water, but that gives rise to confusion in people who like precise definitions and consistency.

Does it? I can't remember the last time I used the term "substance" in the context of chemistry. If it does have one then it has one in an introductory book. But in the practice of doing chemistry you'd just use a more precise term (like, say, mixture, or the name of the substance), or you'd probably just mean it in the more generic sense.

It might be helpful to treat the 2d definition as essentially analytic. In other words, what a "substance" is in the context of defining an "element" is just "one type of atom." However, the definition you quote uses the plural which I think is a little sloppy on its author's part, since it could be that he was generally defining "element" to cover all the various elements and slipped into the plural. Alternatively, It could be the case that the plural was meant to capture the fact that an "element" is any composition of two or more of the same type of atom. The composite of the atoms being what the term "substance" refers to. The 2d possible interpretation also has the attraction of bring the 2d definition more in line with the 1st definition. The definition would then go like: element = substance; substance = two or more of the same type of atom. I don't think the 2d definition you cite excludes that account, but it doesn't exactly where it on its sleeve either, which it should do as a good scientific definition.

So when someone says “have a cup of water” would you interpret that as a cup of a liquid or a cup of molecules?

Neither. I interpret it as a cup of water, and everyone knows what that is. Most children understand this, long before they are introduced to either molecules or the idea of liquid states.

Again, this is just a question of how language is used, nothing more. Trying to milk philosophy out of this will get no one anywhere.