What binds groups of atoms together?

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What binds groups of atoms together?
« on: 10/07/2008 21:57:18 »
gregory asked the Naked Scientists:

If atoms can't come close to each other because their negative electronic clouds repel, then how come so many atoms clump together to form matter? What creates these bonds?

What do you think?


Offline chris

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What binds groups of atoms together?
« Reply #1 on: 13/07/2008 13:33:27 »
Hi Gregory.

In the context of ionic compounds, like sodium chloride (salt), the positively-charged sodium ions and negatively-charged chloride ions electrostatically attract each other and arrange themselves into a lattice so that each sodium is surrounded by chloride, and vice versa. Hence in this instance it is the ionic charges that hold the crystal together.

In a covalently-bonded molecule, such as a hydrocarbon, the atoms share electrons with each other; if an atom tried to move away from another one it would either be left lacking one or more electrons, or have too many electrons. It would consequently be charged, as would the parent molecule it came from. This charge difference would pull the atoms back together; this is effectively what a covalent bond is.

In a metal things are a bit different. Metals are good conductors because there are lots of free or "delocalised" electrons which form a soup that bathes the positively charged metal nuclei. This is why metals are good conductors because the electrons can move about fairly easily. But the same rule as outlined above effectively applies to explain why the substance remains together - because if some metal nuclei tried to leave the substance would end up oppositely charged, and the charge difference would pull them back together.

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