What is the difference between molecular formula, structural formula and skeletal formula?
Question:
Find the molecular formula of a compound having C=40%, H=6.72% the rest is oxygen, and the molecular weight of the compound is found as 180 g/mol.
Answer:
Elements present are;
C = 40%
H = 6.72%
O = (100-{40+6.72}) % = 53.28%
The number of moles of each element present in 100g of the compound;
C = 40g/12gmol-1 = 3.33 mol
H = 6.72g/1gmol-1 = 6.72 mol
O = 53.28g/16gmol-1 = 3.33 mol
The simplest ratio between these elements are found by dividing each value by the largest value among them.
C = 3.33 mol / 6.72 mol = ½
H = 6.72 mol / 6.72 mol = 1
O = 3.33 mol / 6.72 mol = ½
Find the simplest whole number ratio between these atoms;
C = ½ x 2 = 1
H = 1 x 2 = 2
O = ½ x 2 = 1
Hence, the empirical formula of the compound is CH2O.
To find the molecular formula using this empirical formula, we first need to find the number of empirical formula units present in the compound.
Molar mass of empirical formula unit = CH2O = (12 g/mol) + (1g/mol x 2) + (16g/mol)
= 30 g/mol.
The number of empirical formula units present in the compound = 180 gmol-1 / 30 gmol-1 = 6
Then the molecular formula of the compound can be obtained by multiplying the empirical formula by 6.
Molecular formula = (CH2O) x 6 = C6H12O6
What is Structural Formula Structural formula of a compound is the representation of the arrangement of atoms in the compound. This structural formula gives many details about the molecule and the properties of the compound also can be predicted using these details.
The structural formula can be used for the nomenclature of the molecule. This is because the structural formula shows all the functional groups present in the compound and their relative positions. The structural formula can also be used to predict the chemical properties of compound (such as polarity) and physical properties (such as boiling point).
There are few different ways that are used to give the structural formula. Lewis structures show the connectivity of atoms and the lone pairs or unpaired electron in the compound. The condensed formula is another type of structural formula, which gives the relative positions of atoms, but this is not much helpful (Ex: CH3CH2OH is the condensed formula of ethanol).
Figure 1: Lewis Structure of Water Molecule
An important type of structural formula in organic chemistry are skeletal formulas. Most complex organic molecules can be given via skeletal formulas. This type of formulas show the functional groups and their positions. But the hydrogen atoms attached to the carbon atoms are not indicated there.
Figure 2: Ethylene Glycol Skeletal Formula
In stereochemistry, there are many forms of structural formulas. For example, the structural formula indicates the cis-trans geometry of the compound, Newman projection and sawhorse projection of organic compounds, Fischer projection of sugar molecules, Haworth projection, etc.
Question:
Find the molecular formula of a compound having C=40%, H=6.72% the rest is oxygen, and the molecular weight of the compound is found as 180 g/mol.
Answer:
Elements present are;
C = 40%
H = 6.72%
O = (100-{40+6.72}) % = 53.28%
The number of moles of each element present in 100g of the compound;
C = 40g/12gmol-1 = 3.33 mol
H = 6.72g/1gmol-1 = 6.72 mol
O = 53.28g/16gmol-1 = 3.33 mol
The simplest ratio between these elements are found by dividing each value by the largest value among them.
C = 3.33 mol / 6.72 mol = ½
H = 6.72 mol / 6.72 mol = 1
O = 3.33 mol / 6.72 mol = ½
Find the simplest whole number ratio between these atoms;
C = ½ x 2 = 1
H = 1 x 2 = 2
O = ½ x 2 = 1
Hence, the empirical formula of the compound is CH2O.
To find the molecular formula using this empirical formula, we first need to find the number of empirical formula units present in the compound.
Molar mass of empirical formula unit = CH2O = (12 g/mol) + (1g/mol x 2) + (16g/mol)
= 30 g/mol.
The number of empirical formula units present in the compound = 180 gmol-1 / 30 gmol-1 = 6
Then the molecular formula of the compound can be obtained by multiplying the empirical formula by 6.
Molecular formula = (CH2O) x 6 = C6H12O6
What is Structural FormulaStructural formula of a compound is the representation of the arrangement of atoms in the compound. This structural formula gives many details about the molecule and the properties of the compound also can be predicted using these details.
The structural formula can be used for the nomenclature of the molecule. This is because the structural formula shows all the functional groups present in the compound and their relative positions. The structural formula can also be used to predict the chemical properties of compound (such as polarity) and physical properties (such as boiling point).
There are few different ways that are used to give the structural formula. Lewis structures show the connectivity of atoms and the lone pairs or unpaired electron in the compound. The condensed formula is another type of structural formula, which gives the relative positions of atoms, but this is not much helpful (Ex: CH3CH2OH is the condensed formula of ethanol).
Figure 1: Lewis Structure of Water Molecule
An important type of structural formula in organic chemistry are skeletal formulas. Most complex organic molecules can be given via skeletal formulas. This type of formulas show the functional groups and their positions. But the hydrogen atoms attached to the carbon atoms are not indicated there.
Figure 2: Ethylene Glycol Skeletal Formula
In stereochemistry, there are many forms of structural formulas. For example, the structural formula indicates the cis-trans geometry of the compound, Newman projection and sawhorse projection of organic compounds, Fischer projection of sugar molecules, Haworth projection, etc.
