Question

Simple Lewis Structures, Formulas, and Names fo $$ \text { a. }\mathrm{CO} \quad \text { b. } \mathrm{NI}_{3} \quad \text { c. }\mathrm{SiCl}_{4} \quad \text { d. } \mathrm{N}_{4} \mathrm{Se}_{4} $$

Short answer

a. CO: Carbon and oxygen connected by a triple bond with a lone pair on oxygen. b. NI3: Nitrogen in the center with three single bonds to iodine, each iodine with three lone pairs. c. SiCl4: Silicon in the center with four single bonds to chlorine, each chlorine with three lone pairs. d. N4Se4: Alternating single-bonded nitrogen and selenium atoms, with lone pairs on each to satisfy the octet rule.

Step-by-step solution

Determine Total Number of Valence Electrons for CO

Carbon (C) has 4 valence electrons and Oxygen (O) has 6, for a total of 10 valence electrons for the CO molecule.

Draw the Lewis Structure for CO

Place C and O next to each other, forming a triple bond between them (which accounts for 6 electrons), and add one lone pair on the oxygen atom. This will satisfy the octet rule for both atoms.

Determine Total Number of Valence Electrons for NI3

Nitrogen (N) has 5 valence electrons and Iodine (I) has 7 valence electrons each. Since there are 3 iodines, the total number of valence electrons is 5 + 3*7 = 26.

Draw the Lewis Structure for NI3

Place N in the center and arrange three I atoms around it. Each I atom will form a single bond with N. Distribute the remaining 20 electrons as 3 lone pairs on each I atom to satisfy their octet.

Determine Total Number of Valence Electrons for SiCl4

Silicon (Si) has 4 valence electrons and Chlorine (Cl) has 7 valence electrons each. Since there are 4 chlorines, the total number of valence electrons is 4 + 4*7 = 32.

Draw the Lewis Structure for SiCl4

Place Si in the center and arrange four Cl atoms around it. Each Cl atom will form a single bond with Si and have three lone pairs to satisfy their octet, using all 32 electrons.

Determine Total Number of Valence Electrons for N4Se4

Nitrogen (N) has 5 valence electrons and Selenium (Se) has 6 valence electrons each. There are equal numbers of N and Se atoms, so the total number of valence electrons is 4*5 + 4*6 = 44.

Draw the Lewis Structure for N4Se4

We can pair up each N with a Se and form single bonds between them. Then place three lone pairs on each Se atom and one lone pair on each N atom. This will use all 44 electrons and satisfy the octet rule for all atoms.

Key concepts

Valence Electrons

Understanding valence electrons is critical for anyone studying chemistry, especially when it comes to drawing Lewis structures. Valence electrons are the electrons in the outermost shell of an atom that are available for bonding with other atoms.

For instance, in our exercise, carbon has 4 valence electrons whereas oxygen has 6. Knowing the number of valence electrons is the first step in drawing Lewis structures because these electrons are used to form chemical bonds. When determining the total number of valence electrons in a molecule, you simply add up the valence electrons of each atom involved. For the molecule CO, you calculate the total valence electrons by adding 4 (from carbon) and 6 (from oxygen), resulting in a sum of 10 valence electrons.

It's important to remember that elements in the same group in the periodic table have the same number of valence electrons. This commonality allows for predictions regarding their chemical reactivity and the types of bonds they'll form.

Octet Rule

The octet rule is a vital concept in chemical bonding and provides the foundation for Lewis structures. It states that atoms are most stable when they have eight electrons in their valence shell. This rule is based on the electronic configuration of noble gases, which are highly stable due to their filled valence shells.

Applying the octet rule in our exercise helps explain why certain structures are the way they are. For example, the Lewis structure for CO shows a triple bond between carbon and oxygen with a lone pair on oxygen. This arrangement gives each atom eight electrons around it, conforming to the octet rule. Similarly, in SiCl₄, each chlorine atom shares one electron with silicon to complete its octet, while silicon also reaches an octet through its bonds with four chlorine atoms.

Exceptions to the octet rule do occur, especially for molecules or ions that have an odd number of electrons, those with atoms that have more or fewer than eight electrons, and compounds of elements in period 3 and beyond, which can have expanded valence shells.

Chemical Bonding

Finally, chemical bonding is the process by which atoms combine to form compounds. Key types of chemical bonds include ionic, covalent, and metallic bonds. In our exercise, we're focusing on covalent bonds, where atoms share valence electrons.

In the molecule NI₃, each iodine atom forms a single covalent bond with nitrogen, sharing one pair of electrons. In the taught Lewis structure, after forming the single bonds, remaining electrons are placed around the iodine atoms as lone pairs to ensure all iodine and the nitrogen atom achieve the stable octet configuration.

The strength and type of chemical bonds greatly influence the properties of the resulting compounds. For instance, covalent bonds, which involve the sharing of electron pairs between atoms, are directional and can give rise to molecules with specific shapes—an aspect that's crucial in understanding molecular geometry and reactivity.