why are hydrogen molecules called elements but water molecules are called compunds?

Answer 1

The subtle difference here is the number of different elements involved in the species.

In hydrogen there is only one element (although there are two atoms). In water there is more than one element (hydrogen and oxygen), and so it cannot be called an element. Since the two elements are chemically combined, and not simply mixed, the end species is called a compound.

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Answer 2

Hydrogen molecules are still compounds, however Hydrogen in it's natural state forms a diatomic molecule (a molecule with only two components). This happens because hydrogen is much more stable with it's sp1 orbit filled and this covalent bond between two H-H elements foots that bill. Therefore when people say the element hydrogen, if they don't clarify, hydrogen is assumed to be H2.

Answer 3

it's a historical accident. before atoms and molecules were discovered, scientists examined chemical reactions looking for 'elements' - substances which were fundamental, retaining their purity under all transformations. the ancient greeks, you may recall, thought that the elements were earth, air, fire and water. the alchemists discovered many more elements, while showing that some things previously considered elements were not truly so. eventually it was shown that water is not an element because it can be split into oxygen and hydrogen. now we know that elements are composed of identical molecules with only one type of atom (but not necessarily just one atom - hydrogen molecules have two atoms of hydrogen for instance), while compounds are composed of identical molecules with various types of atoms. but this was not obvious when the ideas of element and compound were being developed, so the definitions of element and compound in terms of atoms and molecules now seem a little arbitrary and strange.

Answer 4

The Periodic Table of Elements lists all the elements known to man. These are the smallest division of material on the atomic level. Hydrogen is an element; Water is a compound of two elements; hydrogen (2 atoms) and oxygen.

An element is a basic atom and to break it apart is to totally destroy; as in an atomic bomb.
A compound is composed of various elements. We have billions of compounds available, but they are all created from around 104 different elements. Actually a lot less are used since several of them are radioactive and artificial.

When we see a compound or create one if it is a stable one then we call it a molecule. Molecules can be as complex as DNA or as simple as water. They use atomic bonds to hold themselves together as described by quantum mechanics.

Check this article for the Periodic Table and a list of the elements: http://en.wikipedia.org/wiki/Periodic_table

Answer 5

An element is a pure chemical substance composed of atoms with the same number of protons. A molecule is an arrangement of two or more atoms with a strong chemical bond. Therefore, water is a molecule consisting of two hydrogen atoms and one oxygen atom that have a strong chemical bond.

Answer 6

Because hydrogen is an element and water is a compound. Pay attention in class, read the reading assignments.

Answer 7

because hydrogen, H, is an element and water consits of two different elements, hydrogen, H , and oxygen, O, to be correct it's 2 parts hydrogen and one aprt oxygen, that's why it's called H2O

Answer 8

A lattice is the three dimensional association of species (atoms, molecules and ions)in a solid. It does not inevitably may be the association of metals on my own. organic metals, ionic compounds, supercooled drinks all variety lattices.