Bonding and structure - Chemistry OCR A - As Level

Includes notes on covalent, ionic and metallic bonding, intermolecular forces (hydrogen bonds, van der waals) and dipoles. detailed

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  • Created on: 19-11-11 17:20
Preview of Bonding and structure - Chemistry OCR A - As Level

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Bonding & Structure
Covalent molecules
A covalent bond is the electrostatic attraction between a positively charged nucleus and a shared
pair of electrons
Some molecules have a double bond because two electrons are shared between the same
atom
Example:
CO2 has a double bond because carbon needs 4
electrons and each oxygen atom needs 2
Displayed formula: O=C=O
A dative covalent bond is a covalent bond where only one of the bonded atoms donates both
electrons being shared
Example: Ammonia bonding with Boron Triflouride (NH3 + BF3)
For a molecule to take part in dative covalent bonding, it must have a lone pair of electrons (which it
can donate to the other atom)

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Example: NH4
Shapes of molecules
Without lone pairs
The shape of a simple ion is determined by the number of electrons around the central
atom…read more

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The electron pairs repel each other so that they are as far apart as possible
With lone pairs
Look how each lone pair decreases the bond angle by 2.…read more

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Electronegativity and bond polarity
The electron attracting ability of an atom is called its electronegativity.
Electronegativity: The power of attraction between a bonded atom and a pair of electrons in a
covalent bond
Example: Hydrochloric Acid - HCl
In HCl, Chlorine is more electronegative than
Hydrogen, so it has a greater attraction for
the electrons.
This means that the HCl molecule is polar
with a permanent dipole.…read more

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The same is true for any diatomic molecule where the atoms are identical
Symmetrical and unsymmetrical molecules
In symmetrical molecules, dipoles cancel and there is no overall permanent dipole
Example: CCl4
It has polar covalent bonds/dipoles but as the dipoles cancel each other out
(because it is symmetrical) we say there is no OVERALL DIPOLE
Basically, there is not a positive end and a negative end, like there is
in H20 (which has a dipole)
Intermolecular forces
Molecules in covalent bonding are attracted to each…read more

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Summary: This occurs in symmetrical molecules which have no overall dipole. A molecule with a
temporary dipole induces an opposite, induced dipole into the adjacent molecule. VDW's forces are
very weak and only act for a short period of time to due to fluctuating electron density.
Example: Chlorine
Permanent dipole - dipole forces
If the molecule with atoms of different electronegativities has a + end and a - end, the molecule is
said to have a permanent dipole.…read more

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The interaction between a lone pair of electrons on a N, O or F atom and a Hydrogen atom is shown
.....…read more

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Due to the high strength of hydrogen bonding across the surface of the liquid
Properties of covalent substances
There are two types of covalent molecules:
The atoms within each molecule are The atoms within each molecule are
bonded strongly together by covalent bonded strongly together by covalent
bonds bonds:
o Graphite = hexagonal
arrangement in layers
Small molecules held together by weak o Diamond = tetrahedral
IMF between the molecules arrangement in layers
o
= LOW MELTING POINT
There are no intermolecular
There are no…read more

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Cannot conduct electricity as a solid because the IONS ARE IN FIXED POSITIONS AND ARE
UNABLE TO MOVE FREELY
Can conduct electricity when in solution or molten as THE IONS ARE MOBILE
Water soluble as they disassociate and the charged ions can interact with polar water
molecules
Metallic bonding
Metallic bonding: The electrostatic attraction between positively charged metal ions and
delocalised electrons
In a metal, the electrons in the outer shell are delocalised to give fixed positive metal ions
Properties of metallic substances
Strong metallic…read more

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