Question

Draw Lewis structures of the following simple organic molecules: (a) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH} ;\) (b) \(\mathrm{H}_{3} \mathrm{CCN}\) (c) \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}\).

Short answer

The Lewis structures for the given compounds would depict the bonds between atoms, the lone pairs of electrons, and the formal charges if they exist. The main chains are straight carbon chains, but the groups attached (such as hydroxyl, carbonyl, or amino groups) modify this structure and essentially define the molecule's chemical properties.

Step-by-step solution

Lewis Structure of Propanoic Acid

Propanoic acid has the formula \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{COOH}\). Begin by drawing the carbon chain. Attach the hydrogens to the first two carbon atoms so that they each have four bonds. For the final carbon atom, attach an oxygen atom with a double bond and another oxygen atom with a single bond. Attach a hydrogen to the single bonded oxygen atom.

Lewis Structure of Molecule with Carbonyl and Amino Group

\This molecule has the formula \(\mathrm{H}_{3} \mathrm{CCN}\). Start by drawing the carbon atom and attach three hydrogen bonds to it. Then draw a triple bond to a nitrogen atom. This structure complies with the octet rule as carbon and nitrogen both have eight electrons in their outer orbitals.

Lewis Structure of Ethylamine

Ethylamine has the formula \(\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{NH}_{2}\). Draw the carbon chain first. Then attach three hydrogens to the first carbon, and two to the second one. Finally, attach the nitrogen to the second carbon atom and add two hydrogens to the nitrogen atom. The ammonia group, \(\mathrm{NH}_{2}\), is represented with the nitrogen atom bonded to the two hydrogens.

Key concepts

Chemical Bonding

When atoms come together to form molecules, they do so through a process called chemical bonding. This is a powerful force that involves the sharing, donating, or receiving of electrons between atoms to achieve stability, typically through the attainment of a full valence shell. There are primarily three types of chemical bonds: ionic, covalent, and metallic. In the context of organic molecules, like those seen in the exercise, covalent bonding is key.

Covalent bonds form when two atoms share one or more pairs of electrons. For example, in hydrocarbons, which make up many organic compounds, carbon atoms bond covalently with hydrogen atoms. In drawing Lewis structures for organic molecules, it's important to ensure that the valence electrons are paired correctly to reflect the covalent bonding present within the molecule. This also applies to the bonds between carbon and other elements, such as oxygen or nitrogen, as observed in the molecules given in the exercise.

Organic Molecules

Organic molecules are primarily made up of carbon atoms bonded to each other and to other elements like hydrogen, oxygen, and nitrogen. These molecules are the backbone of countless compounds and are essential for life. They are distinguished by structures like chains and rings, and functional groups which dictate their chemical reactivity.

In organic chemistry, understanding the basic structure of these molecules is crucial, which is where Lewis structures come into play. The exercise provided specifically looks at simple organic molecules: propanoic acid, a molecule with a carbonyl and amino group, and ethylamine, each with distinct functional groups and structural arrangements. Lewis structures are vital to predicting the geometry of the molecules, the arrangement of atoms, and the distribution of electrons within the compound. Such visual tools help students grasp the complexity of organic molecules more intuitively.

Octet Rule

The octet rule is a fundamental principle in chemistry that helps predict the bonding behavior of atoms, particularly in main group elements. It states that atoms are generally more stable when they have eight electrons in their valence shell, akin to the electron configuration of a noble gas. When atoms don't naturally have a complete octet, they tend to form chemical bonds to achieve it.

When drawing Lewis structures, as in the exercise provided, this rule dictates where electrons should be placed around atoms. For example, carbon, a tetravalent atom with four valence electrons, typically forms four covalent bonds to fulfill this rule. Hydrogen, with one valence electron, achieves stability with two electrons. Oxygen and nitrogen also follow this rule by forming enough bonds (and potentially lone pairs) to complete their valence shells. Providing detailed visualization of atoms and their bonds, as Lewis structures do, allows students to better apply and understand the implications of the octet rule in constructing organic molecules.