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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

CO2 has a double bond because carbon needs 4
electrons and…

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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

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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

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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…

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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…

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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
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

Metallic bonding



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