Module 6 & 7 Definitions: Shapes of molecules and Intermolecular Forces & Periodicity

Module 6: Shapes of molecules and Intermolecular Forces

Module 7: Periodicity

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Electron repulsion theory
Electron pairs around the central atom will repel each other so that they are as far apart as possible
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Electronegativity
A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond
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Pure covalent (non-polar) bond (and example molecule, EN difference)
An equally shared pair of electrons between two atoms e.g. H2, EN difference of 0
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Polar covalent bond (and example molecule, EN difference)
An unequally shared pair of electrons between two atoms e.g. HCl, EN difference between 0 and 1.8
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Dipole (and apply e.g. which atom has negative charge)
A separation of electrical charge so one end of a polar molecule has a delta+ charge and the other has a delta- charge, apply: atom with larger EN value has negative charge, atom with smaller EN value has positive charge
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Intermolecular forces
Weak forces of attraction between (dipoles of) different molecules
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London forces (how the arise & where they occur)
Electrons are constantly moving which causes a temporary dipole on one molecule which induces a dipole in a neighbouring molecule, occur between all molecules - important between pure covalent molecules and atoms (noble gases)
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Permanent dipole-dipole interaction
Occurs between (permanent dipoles in different) polar molecules, larger difference in EN = larger dipole = stronger attraction
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Hydrogen bonding
Attraction between the positive dipole on a hydrogen atom and a lone pair of electrons on a negative atom
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Periodicity
A repeating trend in properties of the elements across each period in the periodic table
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First ionisation energy (and equation for Na with state symbols)
The energy required to remove one electron from each atom in one mole of gaseous atoms to form one mole of gaseous 1+ ions, equation: Na (g) --> Na+ (g) + e-
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Second ionisation energy (and equation for Ca)
The energy required to remove one electron from each 1+ ions in one mole of gaseous 1+ ions to form one mole of gaseous 2+ ions, equation: Ca+ (g) --> Ca2+ (g) + e-
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Metallic bonding
Electrostatic attraction between positive metal ions and delocalised electrons
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Other cards in this set

Card 2

Front

A measure of the attraction of a bonded atom for the pair of electrons in a covalent bond

Back

Electronegativity

Card 3

Front

An equally shared pair of electrons between two atoms e.g. H2, EN difference of 0

Back

Preview of the back of card 3

Card 4

Front

An unequally shared pair of electrons between two atoms e.g. HCl, EN difference between 0 and 1.8

Back

Preview of the back of card 4

Card 5

Front

A separation of electrical charge so one end of a polar molecule has a delta+ charge and the other has a delta- charge, apply: atom with larger EN value has negative charge, atom with smaller EN value has positive charge

Back

Preview of the back of card 5
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