Covalent Molecules 1: Intro Flashcards
What is bond strength measured in?
kJ/mol
Why is the bond strength of the C=O bond not a direct double of the C-O bond?
More electrons present in the double bond
Increases repulsion, so although the bond strength is greater, it is not doubled
Why is the bond length of the C=C bond not significantly shorter than the C-C bond?
Also due to repulsion
What is bond length measured in?
Angstrom (Å)
What is electronegativity?
A measure of the tendency of an atom to attract a bonding pair of electrons
Define aliphatic.
An organic compound that is non-aromatic
Has a straight carbon chain
Define aromatic.
A compound that contains a delocalised ring of electrons
What is valency?
How many bonds an atom can form
What are the two characteristics of carbon that give it high chemical versatility?
1) An atom of carbon can form covalent bonds with up to four other atosm
2) An atom of carbon can form multiple covalent bonds - i.e. double or triple bonds
What are hydrocarbons?
Compounds containing only carbon and hydrogen atoms
What are the three groups of hydrocarbon?
Alkane (saturated)
Alkene (containing double bonds)
Alkyne (containing triple bonds)
What are saturated hydrocarbons?
Hydrocarbons containing only single bonds
What are unsaturated hydrocarbons?
Hydrocarbons containing some double or triple bonds
What are halogenoalkanes?
Compounds containing at least one halogen atom attached to either a single carbon or multiple carbon atoms
What is halothane?
1-bromo,1-chloro,2,2,2-trifluoroethane
General anaesthetic
What is chloroform?
Trichloromethane
Was once used as general anaesthetic but was found to be toxic so is no longer used
What are chlorofluorocarbons?
Small molecules with central carbon atoms attached to only fluorine and chlorine
Widely used as refrigerants but found to decay in the stratosphere, converting ozone into molecular oxygen which lacks the ability to absorb UV radiation
Contributing to global warming
What compound has replaced chlorofluorocarbons?
HFCs (hydrofluorocarbons)
Potent greenhouse gases
Warming effect is thought to be thousands of times stronger than carbon dioxide
What is the steroid template?
Four cyclic hydrocarbon rings
Three cyclohexanes and one cyclopentane
Featured in progesterone and testosterone
What are alkyl groups?
Alkane-like skeletons with one hydrogen atom removed to allow the functional group to attach
Represented with R
Why are alkenes more chemically reactive than alkanes?
Because of the presence of the double bond
Valence electrons can be used to participate in new covalent bonds with other atoms
Give two examples of alkenes found in nature.
Limonene - gives oranges and lemons their citrus scent
Geraniol - gives roses their characteristic smell
What are alkynes?
Hydrocarbons containing at least one triple bond
Has extremely high energy so are much less stable than alkanes, but far more reactive
What are aryl groups?
Any aromatic functional group
Represented with ‘Ar’
Eg. phenyl group
What is phenol?
Phenyl group with an -OH attached
Give an example of where aryl groups occur in biological molecules.
Phenylalanine (amino acid)
Adrenaline
Why are hydrocarbons non-polar?
Neither the carbon or hydrogen atom is sufficiently electronegative to cause significant polarity within the molecule
Therefore very few non-covalent interactions can occur
What is the only non-covalent interaction that hydrocarbons experience?
Dispersion forces
The transitory attraction between areas of opposite charge which is a consequence of the continual movement of electrons in a molecule
Why do hydrocarbons have low melting and boiling points?
Requires very little energy to overcome weak dispersion forces
How do melting points change as size of hydrocarbon increases?
As hydrocarbon size increases, melting point also increases as there are greater dispersion forces due to increased number of electrons
Are hydrocarbons soluble in water, and why?
Hydrocarbons are insoluble in water
Because they are non-polar
And unable to form hydrogen bonds
Why do hydrocarbons have few direct roles in biological systems?
They are non-polar
And therefore cannot interact with water molecules
Biological systems are aqueous
What gives alkanes their stability?
Strong covalent bonds
Requires lots of energy to break
Also causes lack of reactivity
What is the symbol for electronegativity and how is it measured?
Chi (ꭓ)
Measured up to the number 4.0
What happens when there is a significant difference in electronegativity between two covalently bonded atoms?
The more strongly electronegative atom will be able to attract the bonding pair of electrons and become ẟ-negative
This starves the other atom of electron density, giving it a ẟ-positive charge
This is a polar bond
