[-_-zzzz]

Hi there,

Water is often described as a "molecule" as well as a liquid which is essentially a group of interacting molecules. So which is it? Does "water" refer to a molecule or a liquid?

[Borek]

It can mean both, depending on the context.

[jeffmoonchop]

normally if you're talking about molecules you say water molecules. If you're pouring a bucket of water over your brothers head for a prank, you say, 'I'm soaked with 1 googol water molecules.'

[-_-zzzz]

It can mean both, depending on the context.

I am quite confused because I often see people online saying “water is a molecule which is a liquid at room temperature”. Doesn’t really make any sense to me. How can a molecule also be a liquid?? I think there is quite a bit of lexical ambiguity in chemistry.

[P]

Water moleculeS in a beaker at room temp/STP are liquid.   Water moleculeS at 0C at standard pressure form a solid.

1 water molecule is 2 hydrogen atoms and 1 oxygen atom. The water molecule is H2O....  water (made from many water molecules) is a liquid at STP and is made up of many water molecules.

Basically, when they say it is a liquid they mean the bulk of many molecules that form the liquid substance.

[jeffmoonchop]

You cant talk about states of matter when you only talk about one molecule. A state is defined by the interactions it has on the molecules around it. If there is one molecule of water floating in the air its a gas, if there's lots of water molecules moving around close together its a liquid, if the water molecules are static its a solid.

[P]

You cant talk about states of matter when you only talk about one molecule. A state is defined by the interactions it has on the molecules around it. If there is one molecule of water floating in the air its a gas, if there's lots of water molecules moving around close together its a liquid, if the water molecules are static its a solid.

Correct. That's why you look at the context of words.  When I use the word 'Man'.   Do I mean the whole of mankind or just one man.  When I say 'sheep'  do I mean 1 sheep or 6 x 10^23 sheep?  When I say 'Oxygen' do I mean 1 atom of Oxgen, 1 molecule of oxygen or 1 litre of oxygen gas?   Same with water - a glass of water is in the order of 10^23 molecules of water....  each molecule is a molecule of water, which fills the glass. The molecular structure is H2O.

@ -_-zzz  -  It's basic language you are struggling with here I think rather than the chemistry   -  does this help?

[-_-zzzz]

You cant talk about states of matter when you only talk about one molecule. A state is defined by the interactions it has on the molecules around it. If there is one molecule of water floating in the air its a gas, if there's lots of water molecules moving around close together its a liquid, if the water molecules are static its a solid.

Correct. That's why you look at the context of words.  When I use the word 'Man'.   Do I mean the whole of mankind or just one man.  When I say 'sheep'  do I mean 1 sheep or 6 x 10^23 sheep?  When I say 'Oxygen' do I mean 1 atom of Oxgen, 1 molecule of oxygen or 1 litre of oxygen gas?   Same with water - a glass of water is in the order of 10^23 molecules of water....  each molecule is a molecule of water, which fills the glass. The molecular structure is H2O.

@ -_-zzz  -  It's basic language you are struggling with here I think rather than the chemistry   -  does this help?

So depending on the context, water can mean a type of molecule or a group of interacting molecules am I correct?

[P]

So depending on the context, water can mean a type of molecule or a group of interacting molecules am I correct?

Pretty much...  but not just any old molecule - H2O in particular is called water. A large number of water molecules in  a glass is called water....  like a sea is called a body of water or just water (although it is full of impurities like salt and minerals - it mainly contains water molecules and it makes up the water).

I hope I am making sense. :-)  Lets look at 'Hydrogen' for a second.  There are 2 hydrogen atoms in a water molecule (H2O) and 1 Oxygen atom. A hydrogen atom is just that - a single hydrogen atom.  A hydrogen molecule is H2, which consists of 2 hydrogen atoms bonded together to make the hydrogen molecule. Hydrogen gas is a large amount of hydrogen molecules mixed up in a single substance which we also call hydrogen or hydrogen gas. All can be called just 'Hydrogen'.  but being more specific the word Hydrogen can cover the Hydrogen atom, the Hydrogen Molecule and the Hydrogen gas. Make sense?

[Borek]

When you say "sand" - do you mean a single grain, a handful, or a dune?

How does it differ from "water"?

(well, it does, water molecule is much more precisely defined than a single grain of sand, still - we use the same word for a single object and for objects in bulk)

[P]

When you say "sand" - do you mean a single grain, a handful, or a dune?

Silica.     

[-_-zzzz]

So depending on the context, water can mean a type of molecule or a group of interacting molecules am I correct?

Pretty much...  but not just any old molecule - H2O in particular is called water. A large number of water molecules in  a glass is called water....  like a sea is called a body of water or just water (although it is full of impurities like salt and minerals - it mainly contains water molecules and it makes up the water).

I hope I am making sense. :-)  Lets look at 'Hydrogen' for a second.  There are 2 hydrogen atoms in a water molecule (H2O) and 1 Oxygen atom. A hydrogen atom is just that - a single hydrogen atom.  A hydrogen molecule is H2, which consists of 2 hydrogen atoms bonded together to make the hydrogen molecule. Hydrogen gas is a large amount of hydrogen molecules mixed up in a single substance which we also call hydrogen or hydrogen gas. All can be called just 'Hydrogen'.  but being more specific the word Hydrogen can cover the Hydrogen atom, the Hydrogen Molecule and the Hydrogen gas. Make sense?

Appreciate the help P. But just another question if that’s ok. Why do I see some websites saying that (for example) “methane is a non-polar molecule which has a low melting point”? So how can a single molecule have a melting point when physical properties are only defined for agglomerations of molecules?

[Borek]

That's just a lousy wording. Methane molecules are non-polar, in effect methane has a low melting point.

[-_-zzzz]

So depending on the context, water can mean a type of molecule or a group of interacting molecules am I correct?

Pretty much...  but not just any old molecule - H2O in particular is called water. A large number of water molecules in  a glass is called water....  like a sea is called a body of water or just water (although it is full of impurities like salt and minerals - it mainly contains water molecules and it makes up the water).

I hope I am making sense. :-)  Lets look at 'Hydrogen' for a second.  There are 2 hydrogen atoms in a water molecule (H2O) and 1 Oxygen atom. A hydrogen atom is just that - a single hydrogen atom.  A hydrogen molecule is H2, which consists of 2 hydrogen atoms bonded together to make the hydrogen molecule. Hydrogen gas is a large amount of hydrogen molecules mixed up in a single substance which we also call hydrogen or hydrogen gas. All can be called just 'Hydrogen'.  but being more specific the word Hydrogen can cover the Hydrogen atom, the Hydrogen Molecule and the Hydrogen gas. Make sense?

Sorry for the inconvenience, but I also often see people saying that H2 is a gas. Would it be more appropriate to say that H2 is a constituent of hydrogen gas?

[Borek]

Again, it is a difference between grain of sand and sand. Many H₂ molecules at RTP/STP are a gas. Single H₂ molecule at any temperature is just an isolated molecule and doesn't have any particular state of matter (as explained earlier by jeffmoonchop).