* If you want to update the article please login/register
Why are some substances chemically bond molecules and others are association of ions? The answer to this question depends upon the electronic structures of atoms and the nature of chemical forces within compounds. Although there are no sharply defined boundaries, chemical bonds are typically classified into three main types: ionic bonds, Covalent bonds, and Metallic bonds. In this chapter, each type of bond will be discussed and general properties found in typical substances in which bond type occur. Ionic bonds result from electrostatic forces that exist between ions of opposite charge. These bonds typically involve metal with nonmetal - covalent bonds that result from sharing of electrons between two atoms. Bonds typically involve one nonmetallic element with another metallic bond. These bonds are found in solid metal with each metal bond to several neighboring groups and bonding electrons free to move throughout the 3 - dimensional structure. Each bond classification is discussed in detail in subsequent sections of the chapter. Let's look at preferred arrangements of electrons in atoms when they form chemical compounds. Figure 8. 11: G. N. Lewis and Octet Rule. Lewis is working in a laboratory. In Lewis ' original sketch for Octet Rule, he initially placed electrons at corners of the cube rather than placing them as we do now. The formula for table salt is NaCl. It is the result of Na + ions and Cl - ions bonding together. If sodium metal and chlorine gas mix under the right conditions, they will form salt. Sodium loses electron, and chlorine gains that electron. In the process, great amount of light and heat is release. The resulting salt is mostly unreactive it is stable. It will not undergo any explosive reactions, unlike sodium and chlorine that it is made of. Why? Referring to the Octet Rule, atoms attempt to get noble gas electron configuration, which is eight valence electrons. Sodium has one valence electron, so giving it up would result in the same electron configuration as neon. Chlorine has seven valence electrons, so if it takes one it will have eight. Chlorine has electron configuration of argon when it gains electron.S The Octet Rule could have been satisfied if chlorine gave up all seven of its valence electrons and sodium took them. In that case, both would have electron configurations of noble gasses, with full valence shell. However, their charges would be much higher. It would be Na 7 - and Cl 7 +, which are much less stable than Na + and Cl -. Atoms are more stable when they have no charge, or small charge.
Writing Lewis Structures, NASA's Cassini - Huygens mission detected a large cloud of toxic hydrogen cyanide on Titan, one of Saturn's moons. Titan also contains ethane, acetylene, and ammonia. What are Lewis structures of these molecules? Calculate the number of valence electrons.: + = 10: + = 14: + = 10: + = 8 Draw skeleton and connect atoms with single bonds. Remember that H is never a central atom: Where needed distribute electrons to terminal atoms: six electrons place on: no electrons remain: no terminal atoms capable of accepting electrons: no terminal atoms capable of accepting electrons where needed place remaining electrons on central atom: no electrons remain: no electrons remain: four electrons place on Carbon: two electrons place on nitrogen Where need, rearrange electrons to form Multiple bonds in order to obtain octet on each atom: form two more C - N bonds: all atoms have correct number of electrons: form triple bond between two Carbon atoms: all atoms have correct number of electrons check Your Learning Both Carbon monoxide, and Carbon dioxide, are products of combustion of fossil fuels. Both of these gases also cause problems: are toxic and have been implicated in global climate change. What are Lewis structures of these two molecules?
Other halogen molecules form bonds like those in chlorine molecule: one single bond between atoms and three lone pairs of electrons per atom. This allows each halogen atom to have a noble gas electron configuration. The tendency of main group atoms to form enough bonds to obtain eight valence electrons is known as the octet rule. The number of bonds that atom can form can often be predicted from the number of electrons needed to reach octet; this is especially true of nonmetals OF second period OF periodic table. For example, each atom OF group 14 element has four electrons in its outermost shell and therefore requires four more electrons to reach the octet. These four electrons can be gained by forming four covalent bonds, as illustrated here for carbon and silicon. Because hydrogen only needs two electrons to fill its valence shell, it is an exception to the octet rule. Transition elements and inner transition elements also do not follow the octet rule: group 15 elements such as nitrogen have five valence electrons in atomic Lewis symbol: one lone pair and three unpaired electrons. To obtain octet, these atoms form three covalent bonds, as in. Oxygen and other atoms in group 16 obtain octets by forming two covalent bonds:
Lewis Dot symbols can be used to predict the number of bonds formed by most elements in their compounds. One convenient way to predict number and basic arrangement OF bonds in compounds is by using Lewis electron Dot symbols, which consist OF chemical symbol for element surrounded by dots that represent its valence of electrons, grouped into pairs often placed above, below, and to the left and right OF symbol. Structures reflect the fact that elements in period 2 and beyond tend to gain, lose, or share electrons to reach a total OF eight valence electrons in their compounds, so - called octet rule. Hydrogen, with only two valence electrons, does not obey the octet rule.
We also use Lewis symbols to indicate the formation of covalent bonds, which are shown in Lewis structures, drawings that describe bonding in molecules and polyatomic ions. For example, when two chlorine atoms form chlorine molecule, they share one pair of electrons: Lewis structure indicates that each atom has three pairs of electrons that are not used in bonding and one share pair of electrons. Dash is sometimes used to indicate shared pair of electrons: single shared pair of electrons is called a single bond. Each atom interacts with eight valence electrons: six in lone pairs and two in single bond.
We use Lewis symbols to describe valence electron configurations of atoms and monatomic ions. Lewis symbols consist of elemental symbols surrounded by one dot for each of its valence electrons: table below shows Lewis symbols for elements of the third period of the periodic table. Lewis symbols can also be used to illustrate formation of cations from atoms, as shown here for sodium and calcium: likewise, they can be used to show formation of anions from atoms, as shown here for chlorine and sulfur: following table demonstrates use of Lewis symbols to show transfer of electrons during formation of ionic compounds.
In 1904, Richard Abegg formulated what is now known as Abegg's Rule, which states that the difference between maximum positive and negative valences of element is frequently eight. This rule was used later in 1916 when Gilbert N. Lewis formulated the Octet Rule in his cubical atom theory. The Octet Rule refers to the tendency of atoms to prefer to have eight electrons in Valence shell. When atoms have fewer than eight electrons, they tend to react and form more stable compounds. Atoms will react to getting in most stable state possible. Complete Octet is very stable because all orbitals will be full. Atoms with greater stability have less energy, so reactions that increase stability of atoms will release energy in the form of heat or light; reactions that decrease stability must absorb energy, getting colder. When discussing the Octet Rule, we do not consider d or F electrons. Only s and p electrons are involved in the Octet Rule, making it a useful rule for main group elements; Octet in these atoms corresponds to electron configurations ending with s 2 p 6. Lewis Dot symbols can also be used to represent ions in ionic compounds. The reaction of cesium with fluorine, for example, to produce ionic compound CsF can be written as follow: no dots are shown on Cs + in product because cesium has lost its single Valence electron to fluorine. Transfer of this electron produces Cs + ion, which has Valence electron configuration of Xe, and F ion, which has a total of eight Valence electrons and Ne electron configuration. This description is consistent with the statement that among main group elements, ions in simple binary ionic compounds generally have electron configurations of nearest noble gas. The charge of each ion is written in product, and anion and its electrons are enclose in brackets. This notation emphasizes that ions are associated electrostatically; no electrons are shared between two elements. As you might expect for such a qualitative approach to bonding, there are exceptions to the Octet Rule, which we describe elsewhere. These include molecules in which one or more atoms contain fewer or more than eight electrons.
Plex.page is an Online Knowledge, where all the summarized are written by a machine. We aim to collect all the knowledge the World Wide Web has to offer.
© All rights reserved
2021 made by Algoritmi Vision Inc.
If your domain is listed as one of the sources on any summary, you can consider participating in the "Online Knowledge" program, if you want to proceed, please follow these instructions to apply.
However, if you still want us to remove all links leading to your domain from Plex.page and never use your website as a source, please follow these instructions.