For neutral molecules, which statements about covalent Lewis structures are true?

8:09 AM    Chemistry , Molecules , Quizlet , Science   

Q. For neutral molecules, which statements about covalent Lewis structures are true:

1.     Hydrogen atoms are often the central atom of a Lewis structure. ❌

2.     Each atom of a Lewis structure must have eight electrons. ❌

3.     For a neutral molecule, the number of electrons in the Lewis structure is the sum of the valence electrons for the atoms. ✅

4.     Electrons of covalent compounds may be shared between atoms.✅

Covalent bonds share electrons in order to form a stable octet around each atom in the molecules. Hydrogen is the exception it only requires 2 electrons (a duet) to be stable.

1. False. Hydrogen atoms can only ever have 2 valence electrons. That is because the first energy level has no p orbitals.

2. False. Hydrogen is a counter-example.

3. True. For a neutral molecule, the number of electrons in the Lewis structure is the sum of the valence electrons for the atoms.

4. True. That's the definition of a covalent compound.

Explanation
Let us illustrate a covalent bond by using H atoms, with the understanding that H atoms need only two electrons to fill the 1s subshell. Each H atom starts with a single electron in its valence shell:

H⋅⋅H

The two H atoms can share their electrons:

H:H

We can use circles to show that each H atom has two electrons around the nucleus, completely filling each atom’s valence shell:

Because each H atom has a filled valence shell, this bond is stable, and we have made a diatomic hydrogen molecule. (This explains why hydrogen is one of the diatomic elements.) For simplicity’s sake, it is not unusual to represent the covalent bond with a dash, instead of with two dots:

H–H

Because two atoms are sharing one pair of electrons, this covalent bond is called a single bond.