2.2.2 Bonding and structure Flashcards
What are the 3 main types of chemical bonds?
Ionic, metallic and covalent
Define ionic bonding.
The electrostatic attraction between positive and negative ions
Define covalent bonding.
The strong electrostatic attraction between a shared pair of electrons and the nucelus of the bonded atoms.
Define metallic bonding.
Electrostatic attraction between the positive metal ions and the sea of delocalised electrons.
Why do giant ionic lattices conduct electricity when liquid but not when solid?
- In a solid state the ions are fixed in the lattice due to the electrostatic forces of attraction so they cant carry a charge
- In a liquid or molten state the forces have been broken, so the ions are free to move and can carry a current.
Why do giant ionic lattices have high melting and boiling points?
As it takes a large amount of energy to overcome the electrostatic forces of attraction
- The higher the charge the higher the m.p/b.p
Why are giant ionic lattices soluble in polar solvents?
Polar solvents attract ions out of the lattice into the solution.
What are single covalent bonds?
- known as ‘sigma’ bonds
- represents 2 electrons in a pair
What are double covalent bonds?
- 4 shared electrons
- only C, N, O can form these
What are triple covalent bonds?
- 6 shared electrons
- only C, N can form these
What is a lone pair?
Electrons in the outer shell of an atom which are not involved in bonding.
What is a dative covalent bond?
- a bond where both of the shared electrons are supplied by one atom
- for this to happen the acceptor ion must be electron deficient
- a dative bond is treated the same as a covalent bond
- can be shown in a diagram by an arrow pointing away from the lone pair
What does expansion of the octet mean?
When a bonded atom has more than 8 electrons in the outer shell
What are the 2 types of covalent structure?
- simple molecular lattice
- giant covalent lattice
Describe the bonding in simple molecular structures.
Atoms within the same molecule are held by strong covalent bonds. Different molecules are held by weak intermolecular forces.
What are two examples of simple molecular structures?
iodine: the two I atoms are held together by a covalent bond, but the molecules are held together by london forces
Ice: The H and O atoms are held together by covalent bonds but the molecules are held together by hydrogen bonds
Why do simple molecular structures have low melting and boiling points?
As only a small amount of energy is needed to overcome the weak intermolecular forces
Why do simple molecular structures not conduct electricity?
As there are no free ions or electrons; all electrons are fixed in covalent bonds
What type of solvent do simple molecular structures dissolve in?
Non polar solvents
Give examples of giant covalent structures
Diamond, graphite and silicon dioxide
What are 3 properties of giant covalent structures?
- high melting and boiling point
- non conductors of electricity except graphite
- insoluble in polar and non polar solvents
How does graphite conduct electricity?
Delocalised electrons present between the layers are able to move freely carrying the charge.
Why do giant covalent structures have high melting and boiling points?
Strong covalent bonds within the molecules need to be broken which requires al ot of energy
Describe the structure of diamond.
3D tetrahedral structure of C atoms, with each C atom bonded to 4 others
