Covalent structures and bonding
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Firstly, using the general trends of electronegativity, please can you explain why sodium hydride is not covalent but consists of the ions Na+ and H-?
Secondly, using the general trends of electronegativity please can you tell me why methane(CH4) has covalent molecular structure and the electrons are evenly shared in the bonds between the carbon and hydrogen atoms in the methane molecules?
Ulex says
The electronegativity of an element is a measure of how strongly its atoms pull a shared pair of electrons towards themselves when bonded to other atoms.
If the two atoms linked by a bond have about the same values of electronegativity, then the electrons are equally shared and the bond is covalent. This is the case with methane.
If the two atoms linked by a bond have have very different values of electronegativity, then the electrons are pulled strongly towards the more electronegative element. This may give rise to polar covalent or ionic bonding depending on how extreme the difference in values is. Hydrogen is much more electronegative than sodium, so sodium hydride is ionic.
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updated: 17 February 2005
