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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…

Page 2

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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

Page 3

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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 2.5o

Lone pair rules:

A lone pair of electrons is held closer to the nucleus than a bonded pair of electrons
Lone…

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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…

Page 5

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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…

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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…

Page 7

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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
.....
by dots



Example: Water - H20




Remember to show all lone pairs, partial charges and hydrogen bonds when drawing
diagrams like the one above


Example: Ammonia - NH3…

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o 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:…

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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…

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