Question

How many sticks did you need to make the skeleton structure? ____________ How many sticks are left over? ____________ If your model is to obey the octet rule each ball must have four sticks in it (except for hydrogen atom balls, which need only one). (Each atom in an octet rule species is surrounded by four pairs of electrons.) How many holes remain to be filled? ____________ Fill them with the remaining sticks, which represent nonbonding electron pairs. Draw the complete Lewis structure for CH3Cl using lines for bonds and pairs of dots for nonbonding electrons.

Short answer

You needed 4 sticks to make the skeleton structure for CH3Cl. There are 3 sticks left over representing nonbonding electron pairs. There are 10 holes to be filled, but only 3 nonbonding electron pairs are available. Rearrange the bonds and electron pairs to satisfy the octet rule and draw the complete Lewis structure: H | H – C – Cl : : : | H

Step-by-step solution

Determine the total number of valence electrons

To determine the total number of valence electrons in the CH3Cl molecule, count the valence electrons of each atom: For Carbon (C): There are 4 valence electrons. For Hydrogen (H): There is 1 valence electron. For Chlorine (Cl): There are 7 valence electrons. Total valence electrons: 4 (C) + 3 * 1 (H) + 7 (Cl) = 4 + 3 + 7 = 14

Determine the skeleton structure and number of sticks needed

For the CH3Cl molecule, the skeleton structure can be written as CH3Cl, with Carbon as the central atom, bonded to three Hydrogen atoms and one Chlorine atom. Using single bonds to connect all the atoms we would need one bond between C-Cl and three bonds between C-H, totalling four bonds. Therefore, you need 4 sticks to make the skeleton structure.

Calculate remaining sticks and holes to be filled

Since each bond in the skeleton structure requires 2 electrons, and we used all single bonds, the total number of electrons used is 4 * 2 = 8. The remaining electron pairs can be calculated as follows: Total electron pairs remaining = (Total valence electrons - Electrons used in the skeleton structure) / 2 = (14 - 8) / 2 = 3 electron pairs. Thus, 3 sticks are left over representing the 3 nonbonding electron pairs. Following the octet rule, each atom (excluding hydrogen) should be surrounded by 8 electrons. Since Carbon has 4 electrons from the 4 single bonds, and Chlorine has 2 electrons from the single bond with Carbon, they both need 4 and 6 additional electrons, respectively, to complete their octet. There are 10 holes to be filled: 4 for Carbon and 6 for Chlorine, whereas there are only 3 nonbonding electron pairs (sticks) left. Therefore, we need to rearrange the bonds and electron pairs to satisfy the octet rule.

Draw the complete Lewis structure

To satisfy the octet rule, the three remaining electron pairs can be used as nonbonding electron pairs on Chlorine. Carbon still needs an additional electron pair to complete its octet. We can convert one of the C-H single bonds to a C-H bond with one nonbonding electron pair on Carbon and one on Hydrogen. The Lewis structure for the CH3Cl molecule would look like this: H | H – C – Cl : : : | H Here, single lines represent single bonds and the pairs of dots represent nonbonding electron pairs.

Key concepts

Valence Electrons

Understanding valence electrons is key to drawing Lewis structures. Valence electrons are the outermost electrons of an atom and are crucial in forming chemical bonds.
Each element's group number in the periodic table can guide you to find the number of valence electrons. For example:

• Carbon (C), found in group 14, has 4 valence electrons.
• Hydrogen (H), with its single position, has 1 valence electron.
• Chlorine (Cl), in group 17, carries 7 valence electrons.

Altogether, in a CH3Cl molecule, you total these up to get 14 valence electrons. This number is crucial as it dictates how atoms connect—through bonds—to satisfy the octet rule.

Octet Rule

The octet rule is a principle that atoms tend to combine so that each atom has eight electrons in its valence shell. This rule gives the atom the same electron configuration as a noble gas.
- **Exceptions include hydrogen**, which only seeks two electrons to fill its outer shell.
In practice, for CH3Cl:

• Carbon attempts to reach this stable arrangement by forming bonds with Hydrogen and Chlorine.
• Chlorine also strives to complete its octet by engaging in bonding and having nonbonding electron pairs.

Applying the octet rule helps determine how many and what type of bonds each atom will form, giving structure to the molecular design.

Nonbonding Electron Pairs

Nonbonding electron pairs, or lone pairs, are valence electrons not involved in bonding. They remain on an atom, adding to its octet without influencing other atoms.
In CH3Cl:

• Chlorine has three lone pairs, symbolized by dots in Lewis structures, that do not participate in bonding.
• While Carbon has no lone pairs due to its full involvement in the single bonding process, this arrangement figures prominently in determining molecular geometry.

Lone pairs are significant because they affect molecular polarity and the distribution of electronic clouds around the molecules, influencing its chemical properties.

CH3Cl Molecular Geometry

The geometry of a molecule like CH3Cl is determined by its atomic arrangement and electron pairs. Using VSEPR (Valence Shell Electron Pair Repulsion) theory, we can predict this arrangement. CH3Cl has a tetrahedral shape, as:

• Carbon acts as the central atom, forming four single bonds with three hydrogen atoms and one chlorine atom.
• The lone pairs on Chlorine don’t distort this shape since they reside on its outer edge.

The tetrahedral shape arises because the electron pairs spread as far apart as possible to minimize repulsion, leading to a 109.5-degree bond angle between atoms in the model. This predictable geometry helps explain the molecule's interactions and behavior with other substances.