Representing Molecules

Molecular formula

actual number of atoms of each element in a molecule

Empirical formula

simplest whole-number ratio of elements in a compound.

How to find molecular formula

• counting the number of atoms of each element

• listing the carbon and hydrogen atoms first

• listing non-carbon or hydrogen elements in alphabetical order

How to find empirical formula

• find simplest whole nuber ratio of the elemnents ( divide by a common factor so long as each atoms proportion is a whole number)

Displayed Formula

• position of every atom and every bond

• single bonds as one line ( C—C)

• double bonds as two lines ( C═O)

• triple bond as three lines ( C≡N)

How to draw displayed formula

• draw the non-hydrogen atoms eg) C, N, Br, O

• fill in the hydrogens with the correct carbon bonds

• you must show every bond and atom to get the mark

Structural formula

• position of all atoms in a molecule without showing any of the individual bonds

Displayed→ Structural

• Collapse any non hydrogen atom along with any other non hydrogen atom into one group

• then remove the bonds

• reorganise the symbols of each group in alphabetical eg) C 1rst , H 2nd , N 3rd, O 4th

• put altogether

• when you have a regular CH3 group, we write that first/as the first cabon

Molecular → Structural Formula

• draw the displayed then group atoms together

• the draw structural

Structural→ Displayed

• locate the groups withing the molecule of structural formula

• then draw all non hydrogen bonds with single lines

• fill in the hydrogens

• check to see if relavent atoms have the number of bonds theyre meant to eg ) C=4 bonds O=2 bonds

• if carbon doesnt have 4 bonds it means it needs a double/triple bond

Structural → Molecular →Empirical

• count up the no of atoms of each element first

• list the carbon and hydrogen atoms first in alphabetical order

• then use the molecular formula to deduce the simplest whole number ratio of atoms