Chapter 7 IONIC AND METALLIC BONDING Objectives You WILL be able to… Determine number of valence electrons in an atom of a representative element Explain how the octet rule applies o atoms of metallic and nonmetallic elements Describe how cations form Explain how anions form Explain the electrical charge of an ionic compound Describe 3 properties of ionic compounds Model the valence electrons of metal atoms Describe the arrangement of atoms in metal Explain the importance of alloys Ions Valence Electrons – Electrons in the highest occupied energy level of an element’s atoms The number of valence electrons determines an element’s properties Group number indicates the number of valence e- The Octet Rule- the achievement of 8 electrons in the highest energy level of an atom Done by losing, gaining, or sharing valence electrons Formation of Cations Cations form when atoms lose valence electrons Metals usually do this because they only have a few valence electrons and they have low ionization energies The loss of valence electrons makes the cation more stable than the atom because there is an complete octet in the valence shell For example: Na = 1s22s22p63s1 and Na + = 1s22s22p6 Monatomic cations are named using the name of the element (ie sodium ion, magnesium ion) Some metals that easily give up valence electrons are… Alkali metals (+1 charge) Alkali Earth Metals (+2 charge) Aluminum (+3 charge) Heavier group IV and V elements (Sn +2 or +4; Pb +2 or +4; Bi +3) Most transition and inner transition elements (Ag+1, Zn +2, Cr +3; most rare earth metals +3) Some transition metals have cations with varying charge depending on what they are bonded with (ie Fe +3 and Fe+2) Formation of Anions Anions form when atoms gain valence electrons The gain of valence electrons makes the anion more stable than the atom because there is now a complete octet in the valence shell For example: Cl = 1s22s22p63s23p5 and Cl - =1s22s22p63s23p6 Anions are named using the root of the element’s name plus the ending –ide (ie. bromide, chloride) Some nonmetals easily acquire electrons… Halogens (-1 charge) Chalcogens (-2 charge) Nitrogen (-3 charge) Polyatomic Ions are comprised of two or more atoms covalently bonded that can be considered as acting as a single particle Ionic Bonds and Ionic Compounds Ionic bonds are formed when the charges on positive ions balance the charges on the negative ions through electrostatic attraction Formula units are the lowest whole number ratio of ions in an ionic compound. Chemical formulas are shorthand ways of showing the amounts and the types of elements in the smallest representative unit Example: NaCl, CaBr2, AlI3 (salts) Electron Dot Formulas-Open and closed circles or x’s Ionic attractions are so strong that almost all ionic compounds are solid with unique crystalline structures The strength of the bonds also leads to high melting points and boiling points Ionic bonds almost always occur between metals and nonmetals Ionic compounds are also good conductors of electricity if dissolved in water or molten Ionic compounds are electrically neutral, therefore the number of positive charges is the same as the number of negative charges. Colors of Ionic Compounds Transition metal ions having partially filled d orbitals usually have a color. For example… NiSO4 FeCl3 CuSO4 Metal cations that have no d electrons or completely filled d orbitals are usually not colored. NaCl MgSO4 CaCl2 ZnCl2 Metals in Bonding Metals have loosely held valence electrons When metal atoms exist in the solid form of a metal all the nuclei share all the valence electrons of all the atoms in the sample “Electron Sea” The “sea of electrons” explains physical properties such as conductivity, malleability, and ductility Metals are arranged in compact and orderly patterns Alloys Mixtures of two or more elements where at least one is a metal Steel, brass (Cu and Zn), bronze Mixing alloys will result in a metal with superior properties than those of the component materials Them’s 22’s son!!!