Basic concepts and alkanes Flashcards
What is a general formula?
An algebraic formula that can describe any member of a family of compounds.
What is the general formula of an alcohol?
CnH2n+1OH
What is a homologous series?
A family of compounds that have the same functional group and general formula, but each successive member differs by CH2.
What is the general formula of an alkane?
CnH2n+2
What is molecular formula?
It gives the actual number of atoms of each element in a molecule.
What is empirical formula?
The simplest whole number ratio of atoms of each element in a compound.
Divide the molecular formula by the smallest number of atoms for a given element in the molecule.
What are aromatic compounds?
They contain a benzene ring.
What are aliphatic compounds?
They contain hydrogen and carbon joined together in straight chains, branched chains or non-aromatic rings.
What are alicyclic compounds?
When an aliphatic compound contains a ring that is not benzene.
What is an alkyl group?
In compounds with a branched carbon skeleton, it is any hydrocarbon branched chain.
The general formula is CnH2n+1.
What are saturated compounds?
They contain only carbon-carbon single bonds.
What are unsaturated compounds?
They contain multiple carbon-carbon bonds.
What are structural isomers?
They have the same molecular formula, but the structural formula is different.
What are chain isomers?
Molecules that have different arrangements of the carbon skeleton.
They have similar chemical properties, but different physical properties, due to the change in shape of the molecule.
What are positional isomers?
The skeleton and functional group can be the same, but the functional group could be attached to a different carbon atom.
They have different physical properties, and chemical can also be different.
What are cycloalkanes?
They have a ring of carbon atoms with 2 hydrogens attached to each carbon.
They have 2 less hydrogens than other alkanes.
What are IUPAC rules?
Count the carbon atoms in the longest continuous chain to get the stem.
Number the chain so the main functional group has the lowest number. Or pick the one with the most side chains.
Put the side chains in alphabetical order after the number it is attached to, at the start.
Use di, tri or tetra if there’s multiple identical things.
What is the bonding in alkanes?
Atomic orbitals on carbon and hydrogen atoms are positioned so that they overlap to form a new, shared orbital lying directly between the bonded atoms.
This type of covalent bond is a sigma bond.
What is the strength of sigma bonds?
The high electron density between the nuclei means there is strong electrostatic attraction between the nuclei and the shared pair of electrons.
So they have high bond enthalpy.
What is the rotation of sigma bonds?
The bonded atoms are free to rotate around the sigma bond, because the atomic orbitals between them will always overlap.
What is a sigma bond?
Overlap of orbitals directly between bonding atoms.
What is the reactivity of alkanes?
Low reactivity because sigma bonds are very strong and so difficult to break.
They are also non-polar - won’t attract positively or negatively charged particles to react with them.
What are the boiling points of alkanes?
It depends on the size and shape.
Small alkanes, e.g. methane, are gases at room temperature and pressure.
Larger alkanes are liquid.
How does the intermolecular forces of alkanes affect boiling points?
The longer the carbon chain, the more induced dipole dipole interactions.
This is because of larger surface contact, and so more electrons to interact.
So it takes more energy to overcome the interactions and boiling point increases.
