Chapter 2 - Chemical bonding and structure (L)
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In metallic bonding, what 2 factors change the melting temperature?
• Size of cation - Number of delocalised electrons per cation
How does the size of the cation affect the melting temperature in metallic bonding?
The bigger the size, the lower the melting temperature- this is because there will be a larger distance between the delocalised electrons and nuclei of the cations
How do the number of delocalised electrons per cation affect the melting temperature?
The larger the number of delocalised electrons per cation, the higher the melting temperature- this is because will be a stronger electrostatic attraction
Why are metals ductile and malleable?
Because the electrons are free moving, and so move with the cation and prevent strong forces of repulsion occurring between cations in one layer and another layer
What is metallic bonding?
The electrostatic attraction between the nuclei of metal cations and delocalised electrons
In ionic bonding, what 2 factors change melting temperature?
• The stronger the ionic charge, the higher the melting temperature • The smaller the ion, the higher the melting temperature
Explain the brittleness of ionic compounds
When a stress is applied on an ionic compound, the layers of ions may slide over one another, causing ions of the same charge to be side by side and repel; this can cause the crystal to break apart
Are ionic compounds soluble?
Yes. This is because polar water molecules are attracted to the positive and negative ions
What is the relationship between bond length and bond strength in covalent bonds?
The shorter the bond length, the stronger the bond
How does electronegativity change from left to right across a period?
Increases from left to right
What is a polar covalent bond?
A covalent bond in which the bonding electrons are unequally distributed, causing one atom to be delta negative and one delta positive
How does electronegativity change down a group?
Decreases down a group
What is electronegativity?
The ability of an atom to attract a bonding pair of electrons in a covalent bond
Shape of 2 bond pairs 0 lone pairs
Linear (e.g. CO2)
Shape of 3 bond pairs 0 lone pairs
Trigonal planar (e.g. BCl3)
Shape of 4 bond pairs 0 lone pairs
Tetrahedral (e.g. CH4)
Shape of 5 bond pairs 0 lone pairs
Trigonal bipyramidal (e.g. PCl5)
Shape of 6 bond pairs 0 lone pairs
Octahedral (e.g. SF6)
Shape of 3 bond pairs 1 lone pair
Trigonal pyramidal (e.g. NH3)
Shape of 2 bond pairs 2 lone pairs
V-shaped (e.g. H2O)
What is the order of electron pair repulsion according to electron pair repulsion theory?
Lone pair-lone pair>lone pair-bond pair>bond pair-bond pair repulsion
How do electron pairs arrange themselves around the central atom?
So repulsion is at a minimum
What are the 3 types of intermolecular forces?
London forces, permanent dipoles and hydrogen bonds
What causes an temporary dipole to be generated?
Electron density on either side of a molecule fluctuates over time- if at any instant the electron density become unsymmetrical, a dipole will be generated