4.4 Intermolecular Forces Flashcards
What happens when covalent substances are boiled or melted?
Only intermolecular forces are broken, the covalent bonds or intramolecules forces are no broken.
Why are some boiling points higher?
The stronger the intermolecular forces the higher the boiling point since more energy must be supplied to overcome the forces between molecules.
What are London forces?
The only intermolecular forces between NON POLAR molecules. London forces are stronger id more electrons are present in the molecules this is generally related to the relative molecular mass, the higher the relative molecular mass the stronger the London forces.
What are dipole dipole forces?
Exist between POLAR molecules, a more positive atom in one molecule attracts a more negative atom in another molecule. If molecules with similar relative molecular masses are compared polar molecules have stronger intermolecular forces and therefore higher melting and boiling points that non polar molecules.
What id hydrogen bonding?
Occurs between molecules if they contain a H atom joined direct to a very electronegative atom such as N, O or F with a lone pair. It is an intermolecular force between the lone pair of the electronegative oxygen, nitrogen or fluorine atom in one molecule and a positive hydrogen atom in another molecule.
How do the intermolecular forces increase in strength?
London forces < dipole dipole forces < hydrogen bonding.
When will a substance dissolve in a solvent?
If the intermolecular forces in the solute and solvent are similar eg pentane (London forces) is readily soluble in hexane (London forces) but insoluble in water (hydrogen bonding). Substance that are able to participate hydrogen bonding will generally be soluble in water as they are able to hydrogen bond to the water.
What is important about giant covalent structures?
They have no individual molecules just covalent bonds between atoms throughout the structure.
How are the atoms in SiO2 arranged in a giant covalent structure?
Each Si is jointed to 4 O atoms and each O atom is joined to 2 Is atoms. SiO2 has high melting point because strong covalent bonds must be broken.
What are the allotropes of carbon?
Diamond, Graphite and Buckminsterfullerene.
What is the bonding in diamond?
Giant covalent structure with covalent bond between all four atoms, tetrahedral arrangement of bone, hexagonal ring of carbon atoms.
What are the properties of diamond?
High melting point and hard since strong covalent bonds must be broken. Does not conduct electricity since theres no free electrons and all atoms are bonded.
What is the bonding in graphite?
Giant covalent structure with layers of atoms joined by covalent bonds, London forces between layers. Each carbon atom forms three bonds, planar hexagonal rings of atoms.
What are the properties of graphite?
High melting point because strong covalent bonds must be broken. Free electrons as carbon forms only three bonds, therefore conducts electricity, 1 electron per carbon atoms free to move along the layers.
What is the bonding in buckminsterfullerene?
C60 molecular structure. Hexagons and pentagons of C atoms. Each carbon dorms 3 bonds, London forces between molecules.
