Chemistry
Polyatomic Ions
Polyatomic ions are ions that contain two or more atoms that are covalently bonded and carry a net electric charge. They are formed when a group of atoms gains or loses electrons, resulting in a charged particle. Polyatomic ions are commonly found in ionic compounds and play important roles in chemical reactions.
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9 Key excerpts on "Polyatomic Ions"
eBook - PDFChemistry
Principles and Reactions
- William Masterton, Cecile Hurley(Authors)
- 2020(Publication Date)
- Cengage Learning EMEA(Publisher)
2-5 Molecules and Ions 39 The ions dealt with to this point (e.g., Na 1 , Cl 2 ) are monatomic; that is, they are derived from a single atom by the loss or gain of electrons. ▼ Many of the most important ions in chemistry are polyatomic, containing more than one atom. Examples include the hydroxide ion (OH 2 ) and the ammonium ion (NH 4 1 ). In these and other Polyatomic Ions, the atoms are held together by covalent bonds, for example, (O uni2014 H) H uni2014 N uni2014 H H H ( ) In a very real sense, you can think of a polyatomic ion as a “charged molecule.” Because a bulk sample of matter is electrically neutral, any ionic compound always contains both cations (positively charged particles) and anions (negatively charged particles). Ordinary table salt, sodium chloride, is made up of an equal number of Na 1 and Cl 2 ions. The structure of sodium chloride is shown in Figure 2.15. Notice that ■ ■ there are two kinds of structural units in NaCl, the Na 1 and Cl 2 ions. ■ ■ there are no discrete molecules; Na 1 and Cl 2 ions are bonded together in a continuous network. Ionic compounds are held together by strong electrical forces between oppositely charged ions (e.g., Na 1 , Cl 2 ). These forces are referred to as ionic bonds . We write 1 2 when describing the charge but 2 1 when using it as a superscript in the formula of an ion. Yttrium c Figure 2.14 The ions of the elements shown are (a) Sc 3 1 , (b) S 2 2 , (c) Y 2 1 . Theodore Gray/Visuals Unlimited/Corbis Charles D. Winters/Science Source Scandium a Sulfur b Na uni002B Na uni002B Cl uni2212 Cl uni2212 Figure 2.15 Sodium chloride structure. In these two ways of showing the structure, the small spheres represent Na 1 ions and the large spheres Cl 2 ions. Note that in any sample of sodium chloride there are equal numbers of Na 1 and Cl 2 ions, but no NaCl molecules. © Cengage Learning/Charles D. Winters Copyright 2016 Cengage Learning.
eBook - ePub- Jeffrey Gaffney, Nancy Marley(Authors)
- 2017(Publication Date)
- Elsevier(Publisher)
Chapter 3Chemical Bonding—The Formation of Materials
Abstract
This chapter covers chemical bonding between atoms and ions and how this affects the chemical properties of the elements. Which elements form ions and the typical charges on the ions are explained. Ionic bonding and covalent bonding are compared in terms of the octet rule and valence bond theory. Polar and nonpolar covalent bonds are explained and their relationship to both electron group geometry and molecular geometry is stressed. Polyatomic Ions are described as a mixed ionic, covalent species. Molecular orbital theory is introduced to explain magnetism, bond order, and hybridization, which will be important in later discussions of the chemistry of carbon. Intermolecular forces, including hydrogen bonding, are discussed with a special Case Study focusing on the special properties of water.Keywords
Ionic bonding; Covalent bonding; Octet rule; Polyatomic Ions; Dipole moment; Molecular orbitals; Hybridization; Resonance; Molecular geometry; Intermolecular forcesOutline3.1Atoms and Ions3.2Ionic Bonding3.3Covalent Bonding3.4Mixed Covalent/Ionic Bonding3.5Molecular Orbitals3.6Molecular Geometry3.7Molecular Polarity3.8Intermolecular ForcesImportant TermsStudy QuestionsProblems3.1 Atoms and Ions
A neutral atom that loses one or more electrons becomes a positively charged ion. This positively charged ion is known as a cation (from the Greek word katá , meaning “down”). A neutral atom that gains one or more electrons has a negative charge and is known as an anion (from the Greek word ánō , meaning “up”). The number of electrons an element will gain or lose is also a periodic property and can generally be predicted from its position in the periodic table as shown in Fig. 3.1 . Atoms will gain or lose electrons to form ions that have electronic configurations which are more stable than the electronic configurations of the parent atoms. For most elements, this means that they will either gain or lose the number of electrons needed to achieve a closed valence shell. Remember from Table 2.9 of Chapter 2
eBook - PDF- John Kenkel(Author)
- 2010(Publication Date)
- CRC Press(Publisher)
When single atoms gain or lose electrons, a monatomic ion forms . When a collective group of atoms has a charge, it is called a polyatomic ion . The prefix mono-refers to one atom, and the prefix poly-refers to many (two or more) atoms . The number of atoms that a polyatomic ion has is variable . Some examples are discussed here . IA 1 2 IIA 3 IIIB IVB VB VIB VIIB VIIIB Transition metals IB IIB IIIA 13 14 15 16 17 18 VIIIA IVA VA VIA VIIA 4 5 6 7 8 9 10 11 12 Representative elements Inner transition metals FIGURE 3.2 An outline of the periodic table showing the locations of the representative elements, the transition elements, and the inner transition elements. 67 Names and Formulas of Compounds The gain or loss of electrons by an atom is not a random event . An atom gains or loses one or more electrons to achieve a more stable state—a state in which the atom possesses a certain number of electrons . The most stable of states is exemplified by the noble gases . Thus the number of electrons rep-resenting stable states is the number of electrons found in the atoms of noble gases, for example, 2 (helium), 10 (neon), and 18 (argon) . Atoms of elements that have an electron count close to those of the noble gases will gain or lose one or more electrons (and become a monatomic ion) in order to have the same count as the nearest noble gas . Because a metal is located on the left side of the periodic table, it tends to lose one or more electrons to obtain an electron count equal to the noble gas that precedes it . Because a nonmetal is located on the right side of the periodic table, it tends to gain one or more electrons to obtain an electron count equal to the noble gas to its right (see Figure 3 .4) . Thus, given the opportunity, chlorine, for example, will gain an electron to become like argon and sodium will lose an electron to become like neon .
eBook - ePubChemistry
With Inorganic Qualitative Analysis
- Therald Moeller(Author)
- 2012(Publication Date)
- Academic Press(Publisher)
We write brackets around these structures and show the charge as a superscript to avoid putting the charge on a specific atom. The charge is distributed over the whole ion. The oxygen atom has six valence electrons and the hydrogen atom one, a total of seven valence electrons. Since the hydroxide ion has eight valence electrons, it has one extra electron and a charge of −1. One valence electron for each of four hydrogen atoms and the normal number of 5 for the nitrogen atom would give a total of 9 electrons. With 8 electrons present, the ammonium ion is short one electron and thus has a + 1 charge. Similarly, the nitrate ion has one more valence electron (24) than the total for three oxygen atoms and one nitrogen atom, and thus a – 1 charge.Compounds like K+ OH− or NH4 + Cl− incorporate both covalent and ionic bonds. The covalent bonds within each polyatomic ion are so strong that the ion remains a single unit in a crystal or in water solution. Therefore, compounds containing Polyatomic Ions are usually classified as ionic compounds.9.15 Writing Lewis formulas for covalent species
The proper approach to writing a Lewis formula for a covalent compound can be summarized as follows:1. Write down the correct arrangement of the atoms in space, using single bonds.2. Calculate the total number of valence electrons available by adding the number of valence electrons for each atom, subtracting 1 for each unit of positive charge, or adding 1 for each unit of negative charge.3. Assign two electrons to each covalent bond.4. Distribute the remaining electrons so that each atom has the appropriate number of nonbonded electrons. For representative elements this number is often enough electrons so that each atom is surrounded by an octet.5. If there are not enough electrons to go around, change some single bonds to multiple bonds.EXAMPLE 9.1
Write suitable Lewis electron dot formulas for (a) the chlorate ion, ClO3 − ; (b) chlorous acid, HClO2 ; and (c) the nitrosyl ion, NO+ .(a) The arrangement of atoms in ClO3 − isbecause compounds containing ClO3 − are known not to have properties typical of peroxide bonds, that is, O—O. The number of valence electrons we have to work with isThe three covalent bonds we have already put in the structure account for 6 electrons, leaving 20 electrons to be distributed. If we place 6 on each of the oxygen atoms and 2 on the chlorine atom, we find that all of the octets are filled using the available electrons:
eBook - PDF- Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2015(Publication Date)
- Openstax(Publisher)
ion composed of a single atom uncharged, subatomic particle located in the nucleus (also, inert gas) element in group 18 system of rules for naming objects of interest element that appears dull, poor conductor of heat and electricity massive, positively charged center of an atom made up of protons and neutrons compound that contains hydrogen, oxygen, and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H + ions when dissolved in water) polyatomic anion composed of a central atom bonded to oxygen atoms (also, series) horizontal row of the periodic table properties of the elements are periodic function of their atomic numbers. table of the elements that places elements with similar chemical properties close together 114 Chapter 2 | Atoms, Molecules, and Ions This OpenStax book is available for free at http://cnx.org/content/col11760/1.9 pnictogen polyatomic ion proton representative element series spatial isomers structural formula structural isomer transition metal unified atomic mass unit (u) element in group 15 ion composed of more than one atom positively charged, subatomic particle located in the nucleus (also, main-group element) element in columns 1, 2, and 12–18 (also, period) horizontal row of the period table compounds in which the relative orientations of the atoms in space differ shows the atoms in a molecule and how they are connected one of two substances that have the same molecular formula but different physical and chemical properties because their atoms are bonded differently element in columns 3–11 alternative unit equivalent to the atomic mass unit Key Equations • average mass = ∑ i (fractional abundance × isotopic mass) i Summary 2.1 Early Ideas in Atomic Theory The ancient Greeks proposed that matter consists of extremely small particles called atoms.
eBook - PDF- Paul Flowers, Klaus Theopold, Richard Langley, William R. Robinson(Authors)
- 2019(Publication Date)
- Openstax(Publisher)
monatomic ion ion composed of a single atom neutron uncharged, subatomic particle located in the nucleus noble gas (also, inert gas) element in group 18 nomenclature system of rules for naming objects 104 2 • Key Terms Access for free at openstax.org of interest nonmetal element that appears dull, poor conductor of heat and electricity nucleus massive, positively charged center of an atom made up of protons and neutrons oxyacid compound that contains hydrogen, oxygen, and one other element, bonded in a way that imparts acidic properties to the compound (ability to release H + ions when dissolved in water) oxyanion polyatomic anion composed of a central atom bonded to oxygen atoms period (also, series) horizontal row of the periodic table periodic law properties of the elements are periodic function of their atomic numbers. periodic table table of the elements that places elements with similar chemical properties close together pnictogen element in group 15 polyatomic ion ion composed of more than one atom proton positively charged, subatomic particle located in the nucleus representative element (also, main-group element) element in columns 1, 2, and 12–18 series (also, period) horizontal row of the period table spatial isomers compounds in which the relative orientations of the atoms in space differ structural formula shows the atoms in a molecule and how they are connected structural isomer one of two substances that have the same molecular formula but different physical and chemical properties because their atoms are bonded differently transition metal element in groups 3–12 (more strictly defined, 3–11; see chapter on transition metals and coordination chemistry) unified atomic mass unit (u) alternative unit equivalent to the atomic mass unit Key Equations Summary 2.1 Early Ideas in Atomic Theory The ancient Greeks proposed that matter consists of extremely small particles called atoms.
eBook - PDF- Young, William Vining, Roberta Day, Beatrice Botch(Authors)
- 2017(Publication Date)
- Cengage Learning EMEA(Publisher)
May not be copied, scanned, or duplicated, in whole or in part. WCN 02-300 Unit 5 Ionic and Covalent Compounds 115 Anions are larger than the atoms from which they are formed primarily because of their added electrons. Consider the formation of the sulfide ion, S 2 2 , from a sulfur atom. The sulfide ion has 18 electrons, 2 more than a sulfur atom. The additional electrons occupy the 3 p subshell, which was already partially occupied in a sulfur atom. The added electrons increase the existing repulsive forces between electrons in the 3 p subshell, causing the electrons to move away from one another. This in turn leads to an expan-sion of the electron cloud and an anion that is larger than the neutral atom. Consider the following isoelec-tronic ions , species with the same num-ber of electrons but different numbers of protons. The ion with the largest radius in this isoelectronic series is O 2 2 , and the smallest ion is Mg 2 1 . The oxide ion has only 8 protons to attract its 10 electrons, whereas the magnesium ion has 12 protons and thus more strongly attracts its 10 electrons. 5.2 Polyatomic Ions and Ionic Compounds 5.2a Polyatomic Ions Polyatomic Ions are groups of covalently bonded atoms that carry an overall positive or negative charge. (Covalent bonds are described in Covalent Bonding, Unit 6.) The formu-las, names, and charges of the common Polyatomic Ions are shown in Interactive Table 5.2.1 and should be memorized. Most Polyatomic Ions are anions; there is only one common poly-atomic cation, the ammonium ion 1 NH 4 1 2 . Protons Electrons Electron Configuration Ion Radius O 2 2 8 10 1 s 2 2 s 2 2 p 6 140 pm F 2 9 10 1 s 2 2 s 2 2 p 6 133 pm Na 1 11 10 1 s 2 2 s 2 2 p 6 102 pm Mg 2 1 12 10 1 s 2 2 s 2 2 p 6 66 pm Interactive Table 5.2.1 Names and Formulas of Common Polyatomic Ions.
eBook - PDF- Leo J. Malone, Theodore O. Dolter(Authors)
- 2012(Publication Date)
- Wiley(Publisher)
Starting with the formula of a compound (either ionic or molecular), the rules are as follows. 1. Check to see whether any ions are involved in the compounds. Write any ions present. a. Metal–nonmetal binary compounds are mostly ionic. b. If Group IA or Group IIA or Al metals (except Be) are part of the formula, ions are present. For example, KClO is K + ClO - because K is a Group IA element and forms only a +1 ion. If K is +1, the ClO must be -1 to have a neutral compound. Likewise, Ba(NO 3 ) 2 contains ions because Ba is a Group IIA element and forms only a +2 ion. The formula also indicates the presence of two nitrate ions. The ions are represented as Ba 2+ and 2(NO 3 - ). c. Compounds composed of nonmetals contain only covalent bonds. 2. For a molecule, add all of the outer (valence) electrons of the neutral atoms. Recall that the number of valence electrons is the same as the column number (or last digit when columns are labeled 1–18). For an ion, add (if negative) or subtract (if positive) the number of electrons indicated by the charge. 3. Write the symbols of the atoms of the molecule or ion in a skeletal arrangement. a. A hydrogen atom can form only one covalent bond and therefore bonds to only one atom at a time. Hydrogen atoms are situated on the periphery of the molecule. b. The atoms in molecules and Polyatomic Ions tend to be arranged symmetrically around a central atom. The central atom is generally a nonmetal other than oxygen or hydrogen. Oxygen atoms usually do not bond to each other. Thus SO 3 has an S surrounded by three O’s. O S O O rather than such structures as S O S O O O O S O O O O C C OBJECTIVE FOR SECTION 9-4 Draw Lewis structures of a number of molecular compounds and polyatomic ionic compounds. 288 CHAPTER 9 The Chemical Bond In most cases, the first atom in a formula is the central atom, and the other atoms are bound to it.
- Morris Hein, Scott Pattison, Susan Arena, Leo R. Best(Authors)
- 2014(Publication Date)
- Wiley(Publisher)
11.4 PREDICTING FORMULAS OF IONIC COMPOUNDS • Chemical compounds are always electrically neutral. • Metals lose electrons and nonmetals gain electrons to form compounds. • Stability is achieved (for representative elements) by attaining a noble gas electron configuration. 11.5 THE COVALENT BOND: SHARING ELECTRONS • Covalent bonds are formed when two atoms share a pair of electrons between them: • This is the predominant type of bonding in compounds. • True molecules exist in covalent compounds. • Overlap of orbitals forms a covalent bond. • Unequal sharing of electrons results in a polar covalent bond. 11.6 ELECTRONEGATIVITY • Electronegativity is the attractive force an atom has for shared electrons in a molecule or polyatomic ion. • Electrons spend more time closer to the more electronegative atom in a bond forming a polar bond. • The polarity of a bond is determined by the electronegativity difference between the atoms involved in the bond: • The greater the difference, the more polar the bond is. • At the extremes: • Large differences result in ionic bonds. • Tiny differences (or no difference) result(s) in a nonpolar covalent bond. C H A P T E R 1 1 R E V I E W KEY TERM ionization energy KEY TERM Lewis structure KEY TERM ionic bond KEY TERMS covalent bond polar covalent bond KEY TERMS electronegativity nonpolar covalent bond dipole 240 CHAPTER 11 • Chemical Bonds: The Formation of Compounds from Atoms • A molecule that is electrically asymmetrical has a dipole, resulting in charged areas within the molecule. −δ +δ H : Cl H Cl � � � � hydrogen chloride • If the electronegativity difference between two bonded atoms is greater than 1.7–1.9, the bond will be more ionic than covalent. • Polar bonds do not always result in polar molecules. 11.7 LEWIS STRUCTURES OF COMPOUNDS PROBLEM-SOLVING STRATEGY: Writing a Lewis Structure 1.
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