L8 - Chemical Bonding (2) Flashcards
Describe the importance of covalent bonds.
- Bonding in organic compounds = building blocks of life
- Determines the shape of molecules
- Responsible for interactions between proteins and receptors / drugs
- Can cause permanent enzyme inhibition
What does polarity of a bond determine?
Intermolecular forces
Polarity of a ____ and polarity of a ________ are different.
Polarity of a bond and polarity of a molecule are different.
What is a covalent bond?
Bond formed by the electrostatic attraction between oppositely charged nuclei through the sharing od electrons.
Why are covalent bonds formed between atoms?
Both atoms aim to attain a stable configuration of the nearest inert gas by sharing one, two or three electron pairs between the combining atoms.
Where are the shared pair of electrons in a covalent bond found?
Shared pair of electrons are localised in a definite space between the nuclei of the 2 atoms.
What type of bond is a covalent bond?
Directional
What atoms is a covalent bond established between?
Established between the atoms of same / different non-metallic elements.
What happens when atomic orbitals overlap?
Molecular orbitals are formed.
Describe the steps for forming correlation diagrams (molecular orbital diagrams).
1) Determine the electronic structure of the atoms involved
2) Construct a correlation diagram:
- Y-axis is energy
- X-axis has atoms on either side with molecule in middle
- Orbitals are placed on x-axis depending on energy
- nσg formed between bonding electrons
- nσu* formed between anti-bonding electrons
- Hexagon style shape made by joining energy levels and bonds /anti-bonds
- Electrons placed on bonds and anti-bonds in the centre
3) Determine the electronic structure of the molecule
4) Calculate: Bond Order = Bonding Electrons - Anti-bonding Electrons
5) Value will provide information on the stability of the bond
What are molecular orbitals?
Linear combinations of atomic orbitals
When atoms interact to form molecules, the overall number of ________ must remain the same.
When atoms interact to form molecules, the overall number of orbitals must remain the same.
How do electrons fill molecular orbitals?
In the same way that they do atomic orbitals; into the lowest energy level first.
Describe a single covalent bond.
1 pair of electrons shared
Describe a double covalent bond.
2 pairs of electrons shared
Describe a triple covalent bond.
3 pairs of electrons shared
What are Lewis structures used for?
Method of describing covalent bonding in polyatomic molecules.
What is shown in Lewis structures?
Show valence electrons as dots / crosses.
Describe the steps for drawing Lewis structures.
1) Draw the electron configuration of the atoms involved
2) Count the valence electrons for all atoms to determine the total number of electrons in the molecule
3) Use pairs of electrons to form a single bond between atoms (bonding pairs)
4) Arrange the remaining electrons around atoms (lone pairs) to satisfy the octet rule
5) If you run out of electrons, use multiple bonds to complete octets
Hydrogen does not follow the octet rule. What rule does it follow?
The duet rule
What factors favour covalent bonding?
- High ionisation energies
- Equal electron affinities
- Equal / similar electronegativity
- High nuclear charge
- Small atomic size
- Number of valence electrons (e.g. gaining / losing 4 valence electrons is very hard, so carbon forms covalent bonds)
Which elements form covalent bonds?
Elements on the right hand side of the periodic table
Which atoms form covalent bonds?
Same / different kinds of atoms with high electronegativity
Describe the features of covalently bonded molecules.
- Don’t ionise
- Equal attraction to electrons to complete octets
