explain why the bond angles found for the molecules below is as given below.
Methane 109.5
Ammonia 107.5
water 104.5
Methane is a tetrahedral shape and those angles are 109.5 degrees.
NH3 is tetrahedral electronic geometry with a lone pair of electrons. The lone pair repels the three H atoms so the angle is a little less than the 109.5.
H2O has two lone pairs so the repulsion is more so. The angle is even less than that of NH3.
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The bond angles in these molecules are a result of the electron pair repulsion theory, also known as VSEPR theory. According to this theory, electron pairs around a central atom will arrange themselves as far apart as possible to minimize repulsion between them.
1. Methane (CH4): In methane, the central carbon atom is surrounded by four hydrogen atoms. Since all the bond pairs around carbon are electron pairs, they repel each other equally. The tetrahedral arrangement, where the bond pairs are as far apart from each other as possible, gives a bond angle of approximately 109.5 degrees.
2. Ammonia (NH3): In ammonia, the central nitrogen atom is surrounded by three hydrogen atoms and one lone pair of electrons. The lone pair of electrons occupies more space compared to a bond pair since they are not involved in bonding. As a result, the bond pair-lone pair repulsion causes the bond pairs to move slightly closer to each other. This slightly decreases the bond angle from the ideal tetrahedral angle. Thus, ammonia has a bond angle of approximately 107.5 degrees.
3. Water (H2O): In water, the central oxygen atom is surrounded by two hydrogen atoms and two lone pairs of electrons. The presence of the two lone pairs of electrons exerts greater repulsion compared to the bond pairs. This further decreases the bond angle compared to ammonia. Consequently, water has a bond angle of approximately 104.5 degrees.
In summary, the bond angles in methane, ammonia, and water are a result of the arrangement of electron pairs around the central atom, which is determined by the electron pair repulsion theory.
The bond angles in molecules are determined by the arrangement of atoms and the arrangement of electron pairs around the central atom. To understand why the bond angles for the given molecules are as given, we need to consider their molecular geometries and the repulsion between electron pairs.
1. Methane (CH4):
Methane is a tetrahedral molecule with a central carbon atom surrounded by four hydrogen atoms. The electron pairs around the carbon atom are arranged in a tetrahedral geometry, where each hydrogen atom is located at one of the four corners of the tetrahedron. This arrangement is achieved because all the hydrogen atoms are equally repelling each other and want to be as far apart from one another as possible. Consequently, the bond angles in methane are approximately 109.5 degrees.
2. Ammonia (NH3):
Ammonia is a pyramidal molecule with a central nitrogen atom surrounded by three hydrogen atoms and one lone pair of electrons. The presence of the lone pair affects the shape of the molecule. The three hydrogen atoms are arranged in a trigonal pyramid, with the lone pair sitting at the apex of the pyramid. The repulsion between the lone pair and the hydrogen atoms causes a slight compression of the bond angles. As a result, the bond angle in ammonia is approximately 107.5 degrees.
3. Water (H2O):
Water is a bent-shaped molecule with a central oxygen atom surrounded by two hydrogen atoms and two lone pairs of electrons. The presence of the two lone pairs affects the shape of the molecule. The electron pairs tend to repel each other, creating a bent or "V" shape. The repulsion between the lone pairs and the hydrogen atoms decreases the bond angles further. Consequently, the bond angle in water is approximately 104.5 degrees.
In summary, the bond angles in methane, ammonia, and water are determined by the repulsion between electron pairs and the resulting molecular geometries.