Chapter 7 Ionic and Metallic Bonding Section 7

Chapter 7 Ionic and Metallic Bonding Section 7. 1 Ions 1

Electrons in the highest occupied energy level of an element’s atoms are called Valence electrons. To find the number of valence electrons in an atom of a representative element, simply look at its group number. Each noble gas (except He) has eight electrons in its highest energy level. 2

Valence Electrons The noble gases, Group 8, 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. 3

Electron dot structure are diagrams that show valence electrons as dots. 4

Electron Dot Diagrams A way of keeping track of valence electrons. How to write them l Write the symbol l Put one dot for each valence electron l Don’t pair up until they have to 5 X

The Electron Dot diagram for Nitrogen § Nitrogen has 5 valence electrons. § First we write the symbol. §Then add 1 electron at a time to each side. §Until they are forced to pair up. 6 N

Write the electron dot diagram for: Na Mg C 7 O F Ne He

Electron Configurations for Cations l Metals lose electrons to attain noble gas configuration. l They make positive ions. l l 8 Na 1 s 22 p 63 s 1 - 1 valence electron or [Ne] 3 s 1 Na+ 1 s 22 p 6 - noble gas configuration

Electron Dots For Cations, e. g. Calcium Metals will have few valence electrons Ca 9

Electron Dots For Cations, e. g. Calcium l l 10 Metals will have few valence electrons These will come off Ca

Electron Dots For Cations, e. g. Calcium l l l 11 Metals will have few valence electrons These will come off Forming positive ions 2+ Ca

Electron Configurations for Anions l Nonmetals gain electrons to attain noble gas configuration. l They make negative ions. l l 12 S 1 s 22 p 63 s 23 p 4 - 6 valence electrons or [Ne] 3 s 23 p 4 S 2 - 1 s 22 p 63 s 23 p 6 - noble gas configuration.

Electron Dots For Anions, e. g. Phosphorus l l Nonmetals will have many valence electrons. They will gain electrons to fill the highest level. P 13 3 P

Practice Use electron dot diagrams to show the following form ions l Al 14 l Cl l C

Stable Electron Configurations l l All atoms react to achieve noble gas configuration Noble gases have 2 s and 6 p electrons. 8 valence electrons Also called the octet rule Ar 15

Octet Rule In forming compounds, atoms tend to achieve the electron configuration of a noble gas. Atoms of metals tend to lose their valence electrons, leaving a complete octet in the next-lowest energy level. Atoms of non metals tend to gain electrons or to share electrons with another nonmetal to achieve a complete oct An atom’s loss of valence electrons produces a cation, or a positively charged ion. 16

17

The gain of negatively charged electrons by a neutral atom produces an anion. Some ions formed by transition metals do not have noble -gas electron configurations, but have pseudo noble-gas electron configurations. 18 For example, Silver (Ag) forms a pseudo noble-gas electron configuration. (4 s 24 p 64 d 10)

Names of ions l Cations keep the name of the metal – – l 19 Ca calcium Ca 2+ calcium ion Anions change ending to – ide – Cl Chlorine - Cl 1 - chloride ion – O Oxygen - O 2 - oxide ion – N Nitrogen - N 3 - nitride ion

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 -. 20

Questions 1. How can you determine the number of valence electrons in an atom of a representative element? Look up the group number of that element 2. Atoms of which elements tend to gain electrons? Atoms of which elements tend to lose electrons? Nonmetals – gain metals - lose 3. How do cations form? How do anions form? Cation – atom loses valence electrons Anion – atom gains valence electrons 21

Section 7. 2 Ions Bonds and Ionic Compounds 22

Ionic Bonding l l l 23 Anions and cations are held together by opposite charges. This is the bond Ionic compounds are called salts. Simplest ratio is called the formula unit. The bond is formed through the transfer of electrons. Electrons are transferred to achieve noble gas configuration.

Ionic Bonding 1+ 1 - Na Cl 24

Ionic Bonding All the electrons must be accounted for! Ca 25 P

Ionic Bonding 2+ Ca 26 P

Ionic Bonding +2 Ca Ca 27 P

Ionic Bonding 2+ Ca Ca 28 P 3 -

Ionic Bonding 29 2+ Ca P 3 -

Ionic Bonding 30 2+ Ca P 3 -

Ionic Bonding 31 Ca 2+ Ca P 3 -

Ionic Bonding 2+ Ca 32 P P 3 - 3 -

Ionic Bonding Ca 3 P 2 Formula Unit 33

Practice 34 l Use electron dot diagrams to show the following elements make an ionic compound and write the formula unit and name the compound. l Mg and Cl

Practice l 35 Na and N

Practice l 36 Al and O

Ionic Compounds l Made up of – – – 37 a positive and negative ion a cation and an anion a metal and a nonmetal

Properties of Ionic Compounds l l l 38 Crystalline structure. A regular repeating arrangement of ions in the solid. Ions are strongly bonded. Structure is rigid. High melting points - because of strong forces between ions. Go to page: 197

Compounds composed of cations and anions are called ionic compounds. Although they are composed of ions, ionic compounds are electrically neutral. Ionic compounds can conduct electric current when melted or dissolved in water, because ions are free to move in the solution. 39 The electrostatic forces that hold ions together in ionic compounds are called ionic bonds. Go to page: 198

Classwork Solve #12, page: 196 Solve #18 & 20, page: 199 40

Section 7. 3 Metallic Bonding

Metallic Bonds & Properties Go to page: 201 Metals are made up of closely packed cations rather than neutral atoms. The valence electrons of metal atoms can be modeled as a sea of electrons. (they are mobile and can drift freely from one part of the metal to another). Metallic bonds consists of the attraction of the free-floating valence electrons from the positively charged metal ion. The sea-of-electrons model explains many physical properties of metals. – – – Good conductors of electrical current because electrons can flow freely. Ductile – they can be drawn into wires. Malleable – they can be hammered or forced into shapes.

Crystalline Structure of Metals The crystalline structures of metals can be compared to the stacking of oranges in the grocery store to save space. Metals are crystalline and they are arranged in very compact and orderly patterns.

Go to page: 202 There are several closely packed arrangements that are possible. • body-centered cubic arrangement • face-centered cubic arrangement • hexagonal close-packed arrangement Body-centered cubic Every atom (except those on the Surface) has eight neighbors.

Crystalline Structure of Metals Face-centered cubic arrangement every atom has twelve neighbors

Hexagonal close-packed arrangement every atom also have twelve neighbors. Because of the hexagonal shape, the pattern is different from the facecentered.

Alloys Very few of the metallic items that you use every day are pure metals. e. g: spoons. Most of the metals you encounter are alloys Alloys are mixtures composed of two or more elements. at least one of which is a metal. The most important alloys today are steels (Fe & C) e. g: Brass (Cu & Zn) Stainless steel (Fe, Cr, C, & Ni) 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.

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)

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.

End of Chapter 7