Bonding Lewis structures, covalent

Although most drugs are molecular compounds, a number of ionic compounds have medical uses. Consider the following partial list of ionic compounds used in medicine. Notice that many of these compounds contain polyatomic ions. The bonding between a metal and a polyatomic ion is ionic. However, the bonding within a polyatomic ion is covalent, the topic of our next section. 

AgNOg Silver nitrate Topical anti-infective agent in solution, used to treat and prevent eye infection, especially in newborn infants 

B3S04 Barium sulfate Given as a contrast medium-or image enhancer-in X-rays 

C3S04 Calcium sulfate Used to make plaster casts 

KMn04 Potassium permanganate Topical anti-infective agent often used to treat fungal infections on the feet 

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Ionic and Covalent Bonding Lewis Structures Bond Character Single,... 

Covalent Bonds, Lewis Structures, and the Octet Rule 8... 

A Simplified View of Covalent Bonding Lewis Structures... 

The polyatomic ions you learned about in Chapter 8 are related to covalent compounds. Although the unit acts as an ion, the atoms within the ion itself are covalently bonded. The structures of these ions can also be represented by Lewis structures. 

Lewis Covalent and Ionic Bonds - Lewis Structures - Octet Rule -Cations and Anions - Lone Pairs - Incomplete Octets - Expanded Octets - Double and Triple Bonds - Oxyacids - Resonance. 

The Covalent Bond Lewis postulated the formation of a covalent bond in which atoms share one or more pairs of electrons. The octet rule was formulated to predict the correctness of Lewis structures. This rule says that an atom other than hydrogen tends to form bonds until it is surrounded by eight valence electrons. 

You learned in Chapter 12 that atoms in molecular compounds and polyatomic ions are held together by covalent bonds. Lewis diagrams show, in two dimensions, how the atoms are connected. However, Lewis diagrams do not show how the atoms are arranged n three dimensions-the actual shape of the molecule. In this chapter you will learn how the distribution of atoms leads to the structure and shape of molecules. It begins with the Lewis diagram, and in case it has been a while since you studied Lewis diagrams, we will review them briefly. Important terms are printed in italics. 

Representing a two electron covalent bond by a dash (—) the Lewis structures for hydrogen fluoride fluorine methane and carbon tetrafluoride become... 

Formal charges are based on Lewis structures m which electrons are considered to be shared equally between covalently bonded atoms Actually polarization of N—H bonds m ammonium ion and of B—H bonds m borohydride leads to some transfer of positive and negative charge respectively to the hydrogens... 

When writing a Lewis structure we restrict a molecule s electrons to certain well defined locations either linking two atoms by a covalent bond or as unshared electrons on a sm gle atom Sometimes more than one Lewis structure can be written for a molecule espe cially those that contain multiple bonds An example often cited m introductory chem istry courses is ozone (O3) Ozone occurs naturally m large quantities m the upper atmosphere where it screens the surface of the earth from much of the sun s ultraviolet rays Were it not for this ozone layer most forms of surface life on earth would be dam aged or even destroyed by the rays of the sun The following Lewis structure for ozone satisfies fhe ocfef rule all fhree oxygens have eighf elecfrons m fheir valence shell... 

Section 1 3 The most common kind of bonding involving carbon is covalent bond ing A covalent bond is the sharing of a pair of electrons between two atoms Lewis structures are written on the basis of the octet rule, which limits second row elements to no more than eight electrons m their valence shells In most of its compounds carbon has four bonds... 

Lewis structure (Section 1 3) A chemical formula in which electrons are represented by dots Two dots (or a line) be tween two atoms represent a covalent bond in a Lewis structure Unshared electrons are explicitly shown and sta ble Lewis structures are those in which the octet rule is sat isfied... 

Lewis Structures of Atoms Commonly Forming Covalent Bonds... 

These structures (without the circles) are referred to as Lewis structures. In writing Lewis structures, only the valence electrons written above are shown, because they are the ones that participate in covalent bonding. For the main-group elements, the only ones dealt with here, the number of valence electrons is equal to the last digit of the group number in the periodic table (Table 7.1). Notice that elements in a given main group all have the same number of valence electrons. This explains why such elements behave similarly when they react to form covalently bonded species. 

In 1923. Lewis published a classic book (later reprinted by Dover Publications) titled Valence and the Structure of Atoms and Molecules. Here, in Lewis s characteristically lucid style, we find many of the basic principles of covalent bonding discussed in this chapter. Included are electron-dot structures, the octet rule, and the concept of electronegativity. Here too is the Lewis definition of acids and bases (Chapter 15). That same year, Lewis published with Merle Randall a text called Thermodynamics and the Free Energy of Chemical Substances. Today, a revised edition of that text is still used in graduate courses in chemistry. 

In Chapter 7, we used valence bond theory to explain bonding in molecules. It accounts, at least qualitatively, for the stability of the covalent bond in terms of the overlap of atomic orbitals. By invoking hybridization, valence bond theory can account for the molecular geometries predicted by electron-pair repulsion. Where Lewis structures are inadequate, as in S02, the concept of resonance allows us to explain the observed properties. 

The Lewis structure of a molecule shows atoms by their chemical symbols, covalent bonds by lines, and lone pairs by pairs of dots. For example, the Lewis structure of HF is H - F . We shall see that Lewis structures are a great help in... 

Each atom in a polyatomic molecule completes its octet (or duplet for hydrogen) by sharing pairs of electrons with its immediate neighbors. Each shared pair counts as one covalent bond and is represented by a line between the two atoms. A Lewis structure does not portray the shape of a polyatomic molecule it simply displays which atoms are bonded together and which atoms have lone pairs. 

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