Question

Bond angle of \(109^{\circ} 28\) ' is found in: (a) \(\mathrm{NH}_{3}\) (b) \(\mathrm{H}_{2} \mathrm{O}\) (c) \(\stackrel{+}{\mathrm{CH}}_{3}\) (d) \({ }^{+} \mathrm{NH}_{4}\)

Short answer

The bond angle of \(109^{\circ} 28'\) is found in \(^{+} \mathrm{NH}_{4}\).

Step-by-step solution

Understand Bond Angles

The bond angle of a molecule is determined by the geometry of the molecule. The bond angle of approximately \(109.5^{\circ}\) is typical for a tetrahedral geometry. It is important to identify which molecule in the options has this geometry.

Analyze Each Molecular Option

- \(\mathrm{NH}_{3}\) is ammonia with a distorted tetrahedral (trigonal pyramidal) shape, due to one lone pair, resulting in a bond angle of \(107^{\circ}\).- \(\mathrm{H}_{2}\mathrm{O}\) is water with a bent shape, due to two lone pairs, resulting in a bond angle of \(104.5^{\circ}\).- \(\stackrel{+}{\mathrm{CH}}_{3}\) is the methyl cation with a planar shape, leading to a bond angle of \(120^{\circ}\).- \(\mathrm{NH}_{4}^{+}\) is the ammonium ion with a regular tetrahedral shape, resulting in a bond angle of exactly \(109.5^{\circ}\).

Identify the Correct Option

Among the given options, \(\mathrm{NH}_{4}^{+}\) has a tetrahedral geometry with a bond angle of \(109^{\circ} 28'\).

Key concepts

Tetrahedral Geometry

Tetrahedral geometry is a fundamental shape in molecular chemistry. It involves four atoms arranged around a central atom, like corners of a tetrahedron. This shape minimizes repulsion between electrons in the chemical bonds according to VSEPR (Valence Shell Electron Pair Repulsion) theory. For a molecule to be classified as having tetrahedral geometry, it should possess bond angles close to the ideal angle of approximately \(109.5^{\circ}\). These angles result from the symmetrical arrangement of atoms around the central atom.

When considering examples, methane \(\mathrm{CH}_4\) is a classic case of a molecule with tetrahedral geometry. Here, each hydrogen atom is evenly spaced, creating an equal bond angle, leading to a perfectly balanced molecular structure. Similarly, the ammonium ion \(\mathrm{NH}_4^+\) also demonstrates this geometry, which is why it has a bond angle of \(109^{\circ} 28'\) or very close to \(109.5^{\circ}\).

Understanding this geometry is crucial because it sets the reference for how different factors, like lone pairs or electric charges, can alter the shape and angles of other molecules.

Molecular Shapes

Molecular shape is a key aspect when discussing the physical and chemical properties of molecules. It helps predict how molecules will interact with one another. The shape is determined by the types of bonds and lone pairs of electrons that influence the spatial arrangement around the central atom.

Remember, the geometry is primarily predicted by the VSEPR theory. It states that electron pairs, whether bonding or non-bonding, will arrange themselves as far apart as possible to minimize repulsion. This leads to specific shapes:

• Linear: Central atom with two bonded pairs, bond angle of \(180^{\circ}\).
• Trigonal planar: Three atoms around the central atom, \(120^{\circ}\) angles.
• Tetrahedral: Four bonds, each \(109.5^{\circ}\).
• Trigonal pyramidal: Similar to tetrahedral but with one lone pair, leading to angle distortion.
• Bent: Derived from tetrahedral with two lone pairs causing a bent shape and even greater angle distortion.

In addition, understanding molecular shapes is important for reactions and polarity considerations, affecting everything from biological processes to material design.

Lone Pairs

Lone pairs refer to pairs of valence electrons that are not involved in bonding. These electron pairs still occupy space around an atom and can greatly affect the geometry and bond angles of a molecule.

Lone pairs exert greater repulsion on surrounding bonds than bonded pairs because they occupy more space. This causes a deviation from the ideal geometry. For example, in ammonia \(\mathrm{NH}_3\), the presence of one lone pair results in a pyramidal shape with a bond angle reduced from the ideal tetrahedral \(109.5^{\circ}\) to approximately \(107^{\circ}\).

Moreover, in water \(\mathrm{H}_2\mathrm{O}\), two lone pairs push the hydrogen atoms closer together, creating a bent shape and reducing the bond angle further to about \(104.5^{\circ}\). These lone pairs can alter properties such as polarity and reactivity, as they influence how the central atom interacts with other atoms or molecules.

Understanding how lone pairs affect molecular shapes aids in predicting molecular behavior and in designing chemicals with specific properties.

Bond Angle Distortions

Bond angle distortion occurs when the angles between bonded atoms in a molecule differ from the ideal geometrical angles. Various factors cause these distortions, primarily the presence of lone electron pairs and the sizes of different atoms involved in the bonds.

Lone pairs are notably more repulsive than bonding pairs, creating additional space demands around the atom, which distorts the angles. For instance, as seen in \(\mathrm{NH}_3\) and \(\mathrm{H}_2\mathrm{O}\), bond angles are reduced due to these repulsions.

Size of atoms also plays a role—larger atoms or electron clouds result in larger spaces that tend to buckle surrounding bond angles. Additionally, multiple bonds can cause distortion due to their increased electron density, affecting the adjacent single bonds.

Recognizing these angle distortions is critical because they can affect molecular polarity and stability. The distortion in bond angles provides insight into reactivity and how molecules might interact with others, which is essential in fields ranging from biological systems to material science.