organic chem + relative atomic mass etc

relative atomic mass Ar

the average of the relative isotopic masses of all the naturally occurring isotopes of an element compared to 1/12 of a carbon-12 atom. The relative percentage abundance of these isotopes are taken into account.

Since it is an average, it is not necessarily a whole number when calculated

no units

relative isotopic mass

the mass of an isotope of an element compared to 1/12 the mass of a carbon-12 atom

mass spectrometer

measures the abundance and relative mass of each isotope in an element

relative molecular mass Mr

how heavy a molecule of compound is compared to an atom of carbon-12

the relative atomic masses of each atom in the molecule

mole

amount of substance

can be used to count atoms, molecules or ions

symbol:n

unit:mol

avogadro’s number

represents the number of atoms of carbon-12 in 12 grams of carbon-12

carbon-12 is used as a standard

molar mass

the mass of one mole of pure substance

symbol : M

unit: g mol^-1

molar mass of a pure element or compound= relative atomic/ molecular mass

but relative atomic mass has no units

empirical formula

shows the simplest ratio of atoms or ions in a compound

give the mole ratio of each element present in a compound

molecular formula

gives the actual number of atoms of each element present

hydrocarbons

molecules containing carbon and hydrogen

alkanes

the series of saturated hydrocarbons containing only single carbon-carbon bonds

molecules are non-polar

general formula CnH2n+2

properties of alkanes

methane

ethane

propane

butane

= gas in room temp

pentane

hexane

heptane

octane

nonane

decane

= liquid in room temp

increases in boiling/ melting point

does not dissolve in water

all are non polar

saturated

physical properties

larger = higher melting point

• larger molecules have more electrons and more instantaneous dipoles

• dispersion forces

• dispersion forces operate over a greater area for longer molecules

• therefore stronger dispersion forces exist between larger molecules

• e,g butane (C4H10) higher boiling point than ethane (C2H6)

alkyl group

side groups

shown in brackets in condensed structural formulas

structural isomers

molecules with the same molecular formula but different arrangements of atoms

reactions of alkanes

generally unreactive but can be used as fuel

they burn and react with oxygen

combustion reaction

alkenes

the series of unsaturated hydrocarbons containing a double carbon-carbon bond

homologous series

general formula CnH2n

homologous series

a group of organic compounds that

have the same functional group

show a gradual trend in physical properties

have similar chemical properties

saturated

all carbon-carbon bonds are single bonds

the molecules contain the maximum number of hydrogen atoms possible

alkene reactions

more reactive than alkanes

can undergo addition reactions

where a double bond is broken and other atoms are added to the hydrocarbon y bonding with a carbon atom

haloalkanes

side group halogen

halo side chain is considered of equal rank as alkyl side chain

follow alphabetical order for prefixes when naming

F = fluoro-

Cl= chloro-

Br= Bromo-

I = iodo-

polarity in haloalkanes

all haloalkanes are polar

halogen atoms are electronegative and they pull/ draw electron density towards themselves.

This results in a partial negative charge on the halogen atoms and leaves carbon atoms with a partial positive charge.

This creates a polar covalent bond

haloalkanes are more reactive than alkanes

reacitons of haloalkanes

substitution reaction

alcohols

have a functional group -OH

called the hydroxyl functional group

name end in ol

properties

• small chain alcohols have a higher boiling point than their corresponding alkanes

• due to hydrogen bonding between alcohol molecules

explaination of this trend

alcohol molecules have polar hydroxyl groups which allows the molecules to attract each other by hydrogen bonding ( as well as weaker dispersion forces between molecules)

non polar alkane molecules only attract each other by weak dispersion forces

therefore, less energy is required to overcome the intermolecular forces between corresponding alkane molecules

when the alcohols are too big however

alcohols with small moleucles dissolve in water

e,g water and ethanol

hydrogen bonds break between water molecules

hydrogen bonds break between ethanol molecules

new hydrogen bonds form between alcohol and water molecules

why larger are not

although it has a polar hydroxy group, the large hydrocarbon portion of this molecule is non polar

the dispersion forces between the long hydrocarbon section of the molecule is stronger than any potential hydrogen bonding between the molecule and water molecules

isomers

same molecular formula but differnet strucutral formula

same empirical formula but differ from each other by the way in which the atoms are arranged

carboxylic acids

have a carboxyl functional group

COOH

end in oic acid

examples in nature

methanoic acid- bee sting

ethanoic acid- vinegar

propanoic acid - preservative

properties

• sour

• weak acids with relatively high boiling point

• sting and cause irritation e.g methanoic acid in ant bites irritates the skin

• small carboxylic acids are soluble in water

  as they can form hydrogen bonds with water molecules

they for dimers

where carboxylic acid molecules form two hydrogen bonds with each other causing the hydrogen bonding between carboxylic acids to be stronger than their corresponding alcohols

results in high boiling points

✅ Carboxylic acids contain both:

• An –OH group (like alcohols)

• A C=O (carbonyl) group

Each of these can participate in hydrogen bonding:

• The –OH can donate an H-bond (via H)

• The C=O can accept an H-bond (via the O)

🔁 So two hydrogen bonds can form between two acid molecules — often forming dimers in non-polar solvents.

❌ Alcohols only have:

• An –OH group
  → So they can donate or accept one H-bond, but not both simultaneously like acids do.

VCE relevance: This explains why carboxylic acids have higher boiling points than alcohols of similar molar mass — stronger intermolecular forces (2 H-bonds per molecule).

Representation	Description
Molecular formula	Shows the number of each type of atom. E.g. C₂H₆O
Condensed formula	Shows grouping but not bonding. E.g. CH₃CH₂OH
Structural formula (semi-structural)	Shows the arrangement of atoms and groups. E.g. CH₃–CH₂–OH
Displayed (full structural) formula	Shows all atoms and all bonds
Lewis dot structure	Shows valence electrons and lone pairs
Skeletal formula	Simplified — carbon atoms are implied, hydrogen atoms on C are omitted

Feature	Lewis Dot Structure	Structural Diagram (Displayed formula)
Shows electron pairs?	✅ Yes (lone pairs & bonding pairs)	❌ No (just bonds)
Shows actual atoms?	✅ Yes	✅ Yes
Focus	Electron distribution and bonding	Atom connectivity and shape
Example (H₂O)	:O: with two lone pairs and 2 bonds to H	H–O–H