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Practice Problems. Symmetry & Point Groups. 1. Determine the symmetry elements and assign the point group of (a) NH 2 Cl, (b) CO 32–, (c) SiF 4, (d) HCN, (e) SiFClBrI, (f) BF 4–. Use VSEPR to find the structure and then assign the point group and identify the symmetry elements. (a) NH 2 Cl. Point group = C s. Symmetry elements: E, σ. (b) CO 32–.
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symmetry, in biology, the repetition of the parts in an animal or plant in an orderly fashion. Specifically, symmetry refers to a correspondence of body parts, in size, shape, and relative position, on opposite sides of a dividing line or distributed around a central point or axis. With the exception of radial symmetry, external form has little rel...
Certain animals, particularly most sponges and the ameboid protozoans, lack symmetry, having either an irregular shape different for each individual or else one undergoing constant changes of form. The vast majority of animals, however, exhibit a definite symmetrical form. Four such patterns of symmetry occur among animals: spherical, radial, biradial, and bilateral.
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In spherical symmetry, illustrated only by the protozoan groups Radiolaria and Heliozoia, the body has the shape of a sphere and the parts are arranged concentrically around or radiate from the centre of the sphere. Such an animal has no ends or sides, and any plane passing through the centre will divide the animal into equivalent halves. The spherical type of symmetry is possible only in minute animals of simple internal construction, since in spheres the interior mass is large relative to the surface area and becomes too large for efficient functioning with increase in size and complexity.
In radial symmetry the body has the general form of a short or long cylinder or bowl, with a central axis from which the body parts radiate or along which they are arranged in regular fashion. The main axis is heteropolar—i.e., with unlike ends, one of which bears the mouth and is termed the oral, or anterior, end, and the other of which, called the aboral, or posterior, end, forms the rear end of the animal and may bear the anus. The main axis is hence termed the oral-aboral, or anteroposterior, axis. Except in animals having an odd number of parts arranged in circular fashion (as in the five-armed sea stars), any plane passing through this axis will divide the animal into symmetrical halves. Animals having three, five, seven, etc., parts in a circle have symmetry that may be referred to, respectively, as three-rayed, five-rayed, seven-rayed, etc.; only certain planes through the axis will divide such animals into symmetrical halves. Radial symmetry is found in the cnidarians (including jellyfish, sea anemones, and coral) and echinoderms (such as sea urchins, brittle stars, and sea stars).
In biradial symmetry, in addition to the anteroposterior axis, there are also two other axes or planes of symmetry at right angles to it and to each other: the sagittal, or median vertical-longitudinal, and transverse, or cross, axes. Such an animal therefore not only has two ends but also has two pairs of symmetrical sides. There are but two planes of symmetry in a biradial animal, one passing through the anteroposterior and sagittal axes and the other through the anteroposterior and transverse axes. Biradial symmetry occurs in the comb jellies.
The concept of symmetry is also applied in botany. A flower is considered symmetrical when each whorl consists of an equal number of parts or when the parts of any one whorl are multiples of that preceding it. Thus, a symmetrical flower may have five sepals, five petals, five stamens, and five carpels, or the number of any of these parts may be a multiple of five.
The number of parts in the pistillate (female) whorl is frequently not in conformity with that in the other whorls, but in such cases the flower is still called symmetrical, provided that the other whorls are normal. A flower in which the parts are in twos is dimerous; in threes, fours, or fives, trimerous, tetramerous, or pentamerous, respectively. Trimerous symmetry is the rule in the monocotyledons, pentamerous the most common in the dicotyledons, although dimerous and tetramerous flowers also occur in the latter group.
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May 31, 2016 · A symmetry operation is an action that leaves an object looking the same after it has been carried out. For example, if we take a molecule of water and rotate it by 180° about an axis passing through the central O atom (between the two H atoms) it will look the same as before.
We will therefore first discuss the general foundations of symmetry and group theory, and then apply them to chemical problems, in particular chemical bonding. Let us first find a definition for symmetry.
Aug 4, 2022 · In biology, symmetry is approximate. For example, plant leaves, while considered symmetric, will rarely match up exactly when folded in half. Furthermore, symmetry may refer only to the external form and not the internal anatomy.
Jun 5, 2015 · In geometry, an object exhibits symmetry if it looks the same after a transformation, such as reflection or rotation. Symmetry is important in art, math, biology and chemistry.
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Sep 24, 2024 · Symmetry refers to a situation where one half of an object, shape, or image is a mirror image of the other half. We can also call symmetry a balanced and proportionate similarity between two halves of an object. Symmetry is often seen in nature, art, and design, where it creates a sense of balance and harmony.
