![]() The net charge of a silica tetrahedron (SiO 4) is –4. As a result of the ionic character, silicon becomes a cation (with a charge of +4) and oxygen becomes an anion (with a charge of –2). The bonds in a silica tetrahedron have some of the properties of covalent bonds and some of the properties of ionic bonds. This structure is the building block of the many important silicate minerals. Silicon and oxygen bond together to create a silica tetrahedron, which is a four-sided pyramid shape with O at each corner and Si in the middle (Figure 2.6). ![]() Although shown here in only two dimensions, diamond has a three-dimensional structure as shown on Figure 2.7. The electrons shown in blue are shared between adjacent C atoms. Figure 2.5 The electron configuration of carbon (above) and the sharing of electrons in covalent C bonding of diamond (right). Graphite itself is soft because the bonding between these layers is relatively weak, and it is used in a variety of applications, including lubricants and pencils. Graphite-based compounds, which are strong because of the strong intra-layer covalent bonding, are used in high-end sports equipment such as ultralight racing bicycles. In the mineral graphite, the carbon atoms are linked together in sheets or layers (Figure 2.5), and each carbon atom is covalently bonded to three others. In the mineral diamond, the carbon atoms are linked together in a three-dimensional framework, where one carbon atom is bonded to four other carbon atoms and every bond is a very strong covalent bond. On the other hand, carbon can share electrons to create covalent bonds. Carbon would need to gain or lose four electrons to have a filled outer shell, and this would create too great a charge imbalance for the ion to be stable. Īn uncharged carbon atom has six protons and six electrons two of the electrons are in the inner shell and four in the outer shell (Figure 2.5). Two electrons are shared (one black and one blue) so that each atom “appears” to have a full outer shell. The electrons are black, in the left atom and blue in the right atom. Figure 2.4 Depiction of a covalent bond between two chlorine atoms. For example, two chlorine atoms, which each seek an eighth electron in their outer shell, can share an electron in what is known as a covalent bond, to form chlorine gas (Cl 2) (Figure 2.4). ![]() Sodium gives up an electron to become a cation (bottom left) and chlorine accepts an electron to become an anion (bottom right).Īn element like chlorine can also form bonds without forming ions. Figure 2.3 A very simplified electron configuration of sodium and chlorine atoms (top). Common table salt (NaCl) is a mineral composed of chlorine and sodium linked together by ionic bonds (Figure 1.4). Electrons can be thought of as being transferred from one atom to another in an ionic bond. Since negative and positive charges attract, sodium and chlorine ions stick together, creating an ionic bond. In changing their number of electrons, these atoms become ions - the sodium loses an electron to become a positive ion or cation, and the chlorine gains an electron to become a negative ion or anion (Figure 2.3). Chlorine readily accepts an eighth electron to fill its third shell, and therefore becomes negatively charged because of an imbalance between the number of protons (17) and electrons (18). Chlorine, on the other hand, has 17 electrons: two in the first shell, eight in the second, and seven in the third. By giving up its lone third shell electron, sodium ends up with a full outer second shell. Sodium readily gives up the third shell electron when it loses this one negative charge, it becomes positively charged. Sodium has 11 electrons: two in the first shell, eight in the second, and one in the third (Figure 2.3). Elements that already have their outer orbits filled are considered to be inert they do not readily take part in chemical reactions. This is accomplished by transferring or sharing electrons with other atoms. As we’ve just seen, an atom seeks to have a full outer shell (i.e., eight electrons for most elements, or two electrons for hydrogen and helium) to be atomically stable.
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