Construct Lewis structure for water: H2O. Build a wedge-and-dash representation model (red for O and white for H) and draw the 3-D representation of this molecule. The Lewis Structure for H2O is as follows: H – O – H. The 3-D representation of water is: H (wedge) – O – H (dash). Then, there are 4 electron domains around the central atom, giving a tetrahedral electron geometry. The molecular shape of water is bent.
The Correct Answer and Explanation is:
Correct Answer:
Lewis Structure for H₂O:
mathematicaCopyEdit H–O–H
..
..
The oxygen atom has two lone pairs of electrons, making a total of 4 electron domains (2 bonding pairs and 2 lone pairs).
3-D Representation:
markdownCopyEdit ..
H / \
O
H \ /
..
In a wedge-and-dash model:
- One hydrogen is drawn with a wedge (coming out of the plane)
- One with a dash (going behind the plane)
- The two lone pairs are placed as dots above and behind the oxygen
Number of Electron Domains: 4
Electron Domain Geometry: Tetrahedral
Molecular Shape: Bent
Explanation:
Water (H₂O) is a molecule composed of two hydrogen atoms and one oxygen atom. To determine its structure, first draw its Lewis structure. Oxygen has six valence electrons. When it forms single bonds with two hydrogen atoms, it uses two of those electrons, leaving four electrons which exist as two lone pairs.
Each bond and lone pair count as an electron domain. Therefore, water has four electron domains around the central oxygen atom. According to VSEPR (Valence Shell Electron Pair Repulsion) theory, electron domains arrange themselves as far apart as possible to minimize repulsion. Four electron domains arrange themselves in a tetrahedral geometry.
Although the electron domains form a tetrahedron, the molecular shape is determined only by the positions of the atoms, not the lone pairs. In water, there are two atoms bonded to oxygen and two lone pairs. This leads to a bent molecular shape.
The lone pairs exert greater repulsion than bonding pairs, compressing the bond angle from the ideal tetrahedral angle of 109.5° to approximately 104.5°. This bent shape and the uneven distribution of charge also give water its polar nature, which contributes to its unique properties like high boiling point and strong surface tension.
The 3-D representation uses a wedge to show a bond coming out toward the viewer and a dash to represent a bond going back into the page. This visual helps depict the actual spatial arrangement of the atoms in a water molecule.
