Chemistry Chapter 15 Ionic Bonding and Ionic Compounds

1. Chemistry Chapter 15Ionic Bonding and Ionic Compounds

2. Sec 15.1 Electron Configuration in Ionic Bonding • Objectives: • Use the periodic table to infer the number of valence electrons in an atom and draw its electron dot structure. • Describe the formation of cations from metals and of anions from nonmetals.

3. Valence Electrons • Valence electrons are responsible for chemical bonding and chemical properties among groups. They are the electrons in the highest occupied energy level of an element’s atom. • The number of valence electrons is related to the group numbers in the periodic table.

4. Valence Electrons • Electron dot structures are diagrams that show the valence electrons as dots around the symbol.

5. Write the electron dot structures for each of the following elements. • Cl • S • Al • Li

6. Electron Configurations for Cations • Gilbert Lewis said atoms form certain kinds of compounds and ions in order to achieve a noble gas configuration, because they are un-reactive. • Octet Rule – in forming compounds and ions, atoms tend to achieve the noble gas electron configuration (8 electrons) • Have 8 valence e- • ns2 np6 – General Formula

7. Octet Rule for Cations • Metals will lose 1 to 3 electrons to achieve a configuration of the nearest noble gas • This makes them a cation (+ charge) • Also happens in chemical bonding Neon

8. Octet Rule for Cations • Group 1A elements have 1 valence e-(lose 1 e-) • Na.→ Na+ + e- • Group 2A elements have 2 valence e- (lose 2 e-) • Mg:→ Mg2+ + 2e- • Group 3A elements (only the metals) have 3 valence electrons to lose. • → Al3+ + 3e- • Using an electron dot structure, show the ionization of Barium:

9. Octet Rule for Cations • For transition metals, the charges vary. • Iron, for example, may lose two or three electrons. • Fe = [Ar]4s23d6 • Fe2+ = [Ar] 3d6 • Fe3+ = [Ar] 3d5 • Write the electron configuration for Zn2+. • Zn =[Ar]4s23d10 • Zn2+ = [Ar]3d10

10. Pseudo Noble Gas Configurations • Some transition metals don’t have noble gas configurations, but can achieve them by moving an s1 electron to make a full d-subshell. • These elements have pseudo noble gas configurations, with d-block electrons in the valence shell. • Silver, copper, gold, cadmium, and mercury are examples (elements at the right of the transition metal block)

11. Write the electron configuration for each of the following: • Cu+ • Cu = [Ar]4s23d9 • Cu+ = [Ar]4s13d9 or [Ar]3d10 • Au+ • Au = [Xe]6s24f145d9 • Au+ = [Xe]6s14f145d9 or [Xe]4f145d10

12. Octet Rule for Anions • Nonmetals will gain 1-3 electrons to achieve the nearest noble gas configuration. The negative charge makes it an anion. • Group 15 nonmetals have 5 valence electrons (gain 3 e- to complete the octet) • + 3e-→ N3- • Group 16 nonmetals have 6 valence electrons (gain 2 e- to complete the octet) • + 2e-→ O2- • Group 17 nonmetals have 7 valence electrons (gain 1 e- to complete the octet) • + e-→ F-

13. Write electron configurations for the following anions. • S2- • [Ne]3s23p4 + 2e-= [Ne]3s23p6 = [Ar] • Cl1- • [Ne]3s23p5+ e-= [Ne]3s23p6 = [Ar] • P3- • [Ne]3s23p3+ 3e-= [Ne]3s23p6 = [Ar] • All of these ions have the same noble gas configuration as argon, since they are row three atoms gaining electrons to become stable.

14. Sec 15.1 Electron Configuration in Ionic Bonding • Did We Meet Our Objectives? • Use the periodic table to infer the number of valence electrons in an atom and draw its electron dot structure. • Describe the formation of cations from metals and of anions from nonmetals.

15. Sec 15.2 Ionic Bonds • Objectives: • List the characteristics of an ionic bond. • Use the characteristics of ionic compounds to explain the electrical conductivity of ionic compounds when melted and when in aqueous solutions.

16. Formation of Ionic Compounds • Ionic compounds are bonded by the electrostatic attraction of a cation (+) to an anion (-). • These bonds are called ionic bonds. • The compound is electrically neutral. • The total positive charge must equal the total negative charge.

17. Use the electron dot structures to predict the formulas of the ionic compounds formed from these elements. • Potassium and Sulfur • Aluminum and Sulfur

18. Write the correct chemical formula for the compounds formed from each pair of ions. • K+ and S2- • K2S • Ca2+ and O2- • CaO • Na+ and SO32- • Na2SO3 • Al3+ and SO42- • Al2(SO4)3

19. Properties of Ionic Compounds • At room temperature ionic compounds properties include… • Repeating Patterns • Crystalline solids • Strong bonds • Minimal repulsion • Stable Structure • High melting points

20. Properties of Ionic Compounds • Coordination numberof an ion is the number of ions of opposite charge that surround the ion in a crystal. • Na+ and Cl- have coordination numbers of 6 in NaCl crystal. They each have six ions surrounding them. • The coordination number depends on the shape of the crystal. The charges and relatives sizes of the ions determines the crystal structure.

21. Properties of Ionic Compounds • The internal structures of crystals are determined by a technique called X-ray diffraction crystallography. • X-rays pass through a crystal are recorded on film. • The pattern on the exposed film shows how ions in the crystal deflect the x-rays.

22. Properties of Ionic Compounds • Ionic compound crystal structures can break down. This occurs when the ionic compound is melted or dissolved. Properties are different in this state: • conduct electricity • Ions dissociate and are free to move

23. Sec 15.2 Ionic Bonds • Did We Meet Our Objectives? • List the characteristics of an ionic bond. • Use the characteristics of ionic compounds to explain the electrical conductivity of ionic compounds when melted and when in aqueous solutions.

24. Sec 15.3 Bonding In Metals • Objectives: • Use the theory of metallic bonds to explain the physical properties of metals. • Describe the arrangements of atoms in some common metallic crystal structures.

25. Metallic Bonds and Metallic Properties • Metals consist of closely packed cations • They are in a “sea” of valence electrons • Metallic bond – consists of the attraction of the free floating valence electrons for the positively charged metal ions.

26. Metal Bonds and Properties • Metallic bonding explains metallic properties • Electricity, ductility, malleability • Valence e- move easily and insulate cations from each other. Under pressure, the metal cations can easily slide past one another.

27. Crystalline Structure of Metals • Metals are also in crystal form • Metal atoms are arranged in very compact and orderly patterns, like tennis balls in a box • Have 3 different arrangements • Body-centered cubic, face-centered cubic, hexagonal close-packed Hexagonal Close-Packed Body-Centered Cubic Face-Centered Cubic

28. Alloys • Alloys are mixtures composed of two or more elements, at least one of which is metal. • Most metals you encounter aren’t pure elements. • Amalgams are alloys that contain mercury.

29. Alloys • Types of alloys • Substitutional alloy – The atoms of the components in an alloy are about the same size, they can replace each other in the crystal. • Interstitial alloy – The atomic sizes are quite different, and the smaller atoms can fit into the interstices (spaces) between the larger atoms.

30. Sec 15.3 Bonding In Metals • Did We Meet Our Objectives? • Use the theory of metallic bonds to explain the physical properties of metals. • Describe the arrangements of atoms in some common metallic crystal structures.