This document summarizes key concepts from Chapter 7 on ionic and metallic bonding. It discusses how valence electrons determine an element's chemical properties. Ions form when atoms gain or lose electrons to achieve stable noble gas configurations. Ionic compounds consist of cation and anion ions with opposite charges that are attracted via ionic bonds. Metals form crystalline structures with mobile valence electrons that provide conductivity and malleability. Alloys combine elements to produce superior properties.
2. valence Electrons Scientists learned that all of the elements within each group of the periodic table behave similarly because they have the same number of valence electrons. valence electrons are the electrons in the highest occupied energy level of an element’s atom. The number of valence electrons largely determines the chemical properties of an element. To find the number of valence electrons in an atom of a representative elements, simply look at its group number Elements of Group IA have one valence electron. Elements in Group 4A have four valence electrons, and so forth
3. valence Electrons The noble gases, Group 8A, are the only exceptions to the group-number rule. Helium has two valence electrons, and all of the other noble gases have eight. valence electrons are usually the only electrons used in chemical bonds. As a general rule, only the valence electrons are shown in electron dot structures. Electron dot structures are diagrams that show valence electrons as dots.
5. The Octet Rule Noble gases, such as neon and argon, are unreactive in chemical reactions. (They are stable) Gilbert Lewis explained why atoms form certain kinds of ions and molecules in the octet rule The Octet Rule - in forming compounds, atoms tend to achieve the electron configuration of a noble gas. An octet is a set of eight. (each noble gas except helium has eight electrons in its highest energy level) Atoms of the metallic elements tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level. Atoms of some nonmetallic elements tend to gain electron or to share electrons with another nonmetallic element to achieve a complete octet.
6. Formation of Cations An atom is electrically neutral because it has equal numbers of protons and electrons; an ion forms when an atoms or group of atoms loses or gains electrons. An atom’s loss of valence electrons produced a cation, or a positively charged ion. For metallic elements, the name of the ion is the same as the name of the element. Although their names are the same, there are many important chemical differences between metals and their cations.
7. Formation of Cations An atom is electrically neutral because it has equal numbers of protons and electrons; an ion forms when an atoms or group of atoms loses or gains electrons. An atom’s loss of valence electrons produced a cation, or a positively charged ion. For metallic elements, the name of the ion is the same as the name of the element. Although their names are the same, there are many important chemical differences between metals and their cations.
8. Formation of Cations Using electron dot structures, you can show the ionization of some elements more simply. Na · Na + + e - Sodium atom Sodium ion electron neutral 1 unit of + charge 1 unit of - charge · Mg · Mg 2+ + 2e - Magnesium atom Magnesium ion electron neutral 2 unit of + charge 2 units of - charge
9. Transition Metals For transition metals, the charges of cations may vary. An atom of iron (Fe) may lose two, or three electrons forming either Fe 2+ or Fe 3+ ions. Some ions formed by transition metals do not have noble gas electron configurations and are therefore exceptions to the octet rule. Ag is an example - 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 4d 10 5s 1 To achieve the structure of krypton, which is the preceding noble gas, a silver atom would have to lose eleven electrons.
10. Transition Metals Ions with charges of three or greater are uncommon, and losing eleven electrons is highly unlikely. If Ag loses its 5s 1 electron, the configuration that results, ( 4s 2 4p 6 4d 10 ) with 18 electrons in the outer energy level and all of the orbitals filled, is relatively favorable in compounds. Such a configuration is known as pseudo noble-gas electron configuration. Ag forms a positive ion (Ag + ) in this way.
11. Formation of Anions The gain of negatively charge electrons by a neutral atom produces an anion. The name of an anion of a nonmetallic element is not the same as the element name. The name of the ion typically ends in -ide. Chlorine atom (Cl) forms a chlor ide ion (Cl - ) Oxygen atom (O) forms an ox ide ion (O 2- ) Because they have relatively full valence shells, atoms of nonmetallic elements attain noble-gas electron configurations more easily by gaining electrons than by losing them.
12. Formation of Anions Chlorine belongs to Group 7A and has seven valence electrons. A gain of one electron gives chlorine an octet and converts a chlorine atom into a chloride ion. Atoms of nonmetallic elements form anions by gaining enough valence electrons so as to attain the electron configuration of the nearest noble gas. The chloride ion has the same electron configuration as the noble gas argon. Chloride ion (Cl - ) 1s 2 2s 2 2p 6 3s 2 3p 6 Argon (Ar) 1s 2 2s 2 2p 6 3s 2 3p 6
13. Food For Thought Chlorine atoms need one more valence electron to achieve the electron configuration of the nearest noble gas. Any electron in an atom outside the noble gas core is called a valence electron. Various atoms of the representative elements form ions and gain a noble-gas electron configuration
14. Formation of Anions Halide ions – the ions that are produced when atom of chlorine and other halogens gain electrons All halogen atoms have seven valence electrons and need to gain only one electron to achieve the electron configuration of a noble gas. All halide ions (F - , Cl - , Br - , and I - ) have charge of 1 - .
15. Questions How can you determine the number of valence electrons in an atom of a representative element? Look up the group number of that element Atoms of which elements tend to gain electrons? Atoms of which elements tend to lose electrons? Nonmetallic – gain metallic - lose How do cations form? How do anions form? Cation – atom loses valence electrons Anion – atom gains valence electrons
17. Formation of Ionic Compounds Compounds composed of cations and anions are called ionic compounds . Ionic compounds are usually composed of metal cations and nonmetal anions. Ex: NaCl is formed from Na + + Cl - Although they are composed of ions, ionic compounds are electrically neutral. The total + charge of the cations equals the total – charge of the anions. Anions and cations have opposite charges and attract one another by means of electrostatic forces. The electrostatic forces that hold ions together in ionic compounds are called ionic bonds .
18. Formation of Ionic Compounds Compounds composed of cations and anions are called ionic compounds . Ionic compounds are usually composed of metal cations and nonmetal anions. Ex: NaCl is formed from Na + + Cl - Although they are composed of ions, ionic compounds are electrically neutral. The total + charge of the cations equals the total – charge of the anions. Anions and cations have opposite charges and attract one another by means of electrostatic forces. The electrostatic forces that hold ions together in ionic compounds are called ionic bonds .
19. Formation of Ionic Compounds Look at the reaction of a Na atom and a chlorine atom. Na has 1 valence electron that it can easily lose. (Na is in group 1 A of the representative elements, thus has 1 valence electron) Cl has seven valence electrons and can easily gain one electron. (Cl is in group 7 A of the representative elements, thus has 7 valence electrons) If Na loses its valence electron it achieves the stable electron configuration of neon. If Cl gains a valence electron, it achieves the stable electron configuration of argon. (Remember the Octet Rule)
20. Formation of Ionic Compounds When Na and Cl react, the Na atom gives its one valence electron to a Cl atom. They react in a 1:1 ratio and both ions have stable octets. + Na + Cl - 1s 2 2s 2 2p 6 1s 2 2s 2 2p 6 3s 2 3p 6
34. Alloys Very few of the metallic items that you use every day are pure metals. Ex: spoons. Most of the metals you encounter are alloys. Alloys are mixtures composed of two or more elements., at least on of which is a metal. Ex: Brass (Cu & Zn) Alloys properties are often superior to those of their component elements. Sterling silver (92.5% silver & 7.5% copper) is harder and more durable than pure silver, but still soft enough to be made into jewelry and tableware.
35. Alloys Bronze – 7 parts copper to 1 part tin. Bronze is harder than copper and more easily cast. Nonferrous (non-iron) alloys are commonly used to make coins. The most important alloys today are steels. Alloys can form from their component atoms in different ways. If the atoms of the components in an alloy are about the same size, they can replace each other n the crystal. (substantial alloy) If the atomic sizes are different, the smaller atoms can fit into the spaces between the larger atoms. (interstitial alloy)
36. Questions How do chemists model the valence electrons in metal atoms? Metal cations surrounded by a sea of mobile valence electrons. How can you describe the arrangement of atoms in metals? Atoms in metals are arranged in a compact and orderly manner Why are alloys more useful than pure metals? Their properties are often superior to their component elements.
