Use VSEPR theory to predict the molecular geometry around either carbon atom in acetylene, C2H2.
The Answer is linear. How do you figure out the answer is linear? I know you draw the lewis structure but when I drew it I thought the answer would be tetrahedral, because the carbon atom has 4 lone pairs around it??
it has two carbon atoms, not one. Carbons have a triple bond between them
H-C≡C-H where * means a triple bond.
I don't know how Bob Pursley drew a triple bond (and I think the * means he doesn't know he did, either). That's great if we knew how to do it.
To predict the molecular geometry using the VSEPR (Valence Shell Electron Pair Repulsion) theory, we consider the number of bonding and non-bonding electron pairs around the central atom.
In the case of acetylene, C2H2, start by drawing the Lewis structure:
H – C ≡ C – H
In the Lewis structure, each carbon atom forms a triple bond with an adjacent carbon atom and a single bond with a hydrogen atom. Therefore, each carbon atom has two regions of electron density - the triple bond and the single bond attached to the hydrogens.
Based on VSEPR theory, the electron pairs around each carbon atom will repel each other and try to get as far apart as possible. Since there are two electron pairs, the molecular geometry is linear. It is important to note that the lone pairs on the carbon atoms do not contribute to the molecular geometry since they are not bonded to any other atom.
Thus, the molecular geometry around each carbon atom in acetylene is linear, even though there are additional lone pairs on the carbon atoms.
To determine the molecular geometry around a carbon atom using VSEPR theory, we need to follow a few steps:
Step 1: Draw the Lewis structure of the molecule.
The Lewis structure of acetylene (C2H2) can be represented as follows:
H-C≡C-H
In this structure, each carbon atom forms a triple bond with each other and has two hydrogens attached.
Step 2: Count the total number of electron groups around the central atom.
In both carbon atoms, there are three electron groups: one triple bond and two single bonds.
Step 3: Determine the electron geometry.
The electron geometry is based on the total number of electron groups. In our case, both carbon atoms have three electron groups, so the electron geometry is trigonal planar.
Step 4: Determine the molecular geometry.
The molecular geometry is determined by considering the arrangement of atoms around the central atom. In acetylene, each carbon atom is bonded to one hydrogen atom and the other carbon atom. The arrangement of atoms is linear.
Therefore, the molecular geometry around both carbon atoms in acetylene is linear. The presence of lone pairs does not affect the molecular geometry in this case, as acetylene does not have any lone pairs on the carbon atoms.