Ionic & Metallic Bonding Chapter 7

7.1 Ions Ions are atoms that have gained or lost electrons…. Have a net electrical charge Cations & Anions Valence electrons are lost when cations are formed Electrons are gained by the valence shell when anions are formed.

Valence Electrons & Core Electrons Ve’s are the outermost electrons In the highest s and p sublevels Core electrons are the remaining inner electrons 1s1 1s2 2s2 2p2 1s2 2s2 2p3 1s2 2s2 2p4 1s2 2s2 2p6 3s2 3p5 1s2 2s2 2p6 3s2 3p6 4s1

Valence electrons Number of valence electrons largely determines properties of the element and its group Elements within a group have the same number of valence electrons…Why? Number of ve’s indicated by the group A group numbers, IA, IIA, IIIA, etc. Or count left to right, skipping transition metals

Valence Electrons 1s1 1s22s22p2 1s22s22p3 1s22s22p4

Lewis (Electron Dot) Structures Valence electrons represented as dots

What is the octet rule? Noble gases are extremely unreactive, i.e. very stable When forming ions or compounds, representative elements (Group A) gain, lose, or share electrons in order to achieve a noble gas electron configuration i.e. an octet, ns2np6

Metals vs. Nonmetals Metals tend to give up ve’s to achieve an octet Nonmetals tend to gain or share ve’s to achieve an octet

Formation of Cations Na∙ → Na+ + e- When Na loses its valence electron, there is an octet in the next lowest energy level Using electron dot (Lewis) structures… Na∙ → Na+ + e-

Formation of Cations The electron configuration of the sodium ion is the same as that of a neon atom.

Transition Metals Do not follow the octet rule “Pseudo-noble gas” configuration

Formation of Anions Non-metals tend to gain ve’s to achieve an octet (noble gas e- configuration)

Formation of Anions Using electron dot (Lewis) structures…

Formation of Anions Both a chloride ion and the argon atom have an octet of electrons in their highest occupied energy levels.

How can you predict the charge of a monatomic ion? Determine number of ve’s Representative elements will gain or lose the least number of ve’s to achieve an octet Predict the charge of the aluminum ion.

Can you do it? Use the octet rule to predict the charge B and S ions How many valence electrons does it have? Is it a metal or non-metal? Will it gain or lose electrons? If so, how many? Write an equation using Lewis structures to show the formation of The boron ion (Examples pp. 189-190) The sulfide ion (Examples pp. 191-192)

Common Anions

7.2 Ionic Compounds If ionic compounds are composed of (+) and (-) ions, what type of elements are most likely to be found in them? What types of elements form cations? What types of elements form anions? Usually composed of a metal and non-metal

Ionic Bonds & Ionic Compounds Ionic bonds are electrostatic forces that hold cations and anions together Ionic compounds are composed of cations and anions Are electrically neutral

Ionic Bonds Electrostatic forces of attraction between oppositely charged ions Very strong bonds

Formula Unit Chemical formula for an ionic compound Lowest whole number ratio of ions in the compound producing an electrical neutrality What is the formula unit for… Sodium chloride Magnesium chloride Sodium sulfide Magnesium oxide

What are the properties of ionic compounds? Solids Brittle High melting points Evidence of very strong bonds 3D arrangement of ions Coordination number Electrolytes (conduct electric current when dissolved in water or molten

Crystalline Solids: Specific 3D Arrangement of Ions “crystal lattice”

Coordination Number Number of ions surrounding an oppositely charged ion

High melting temperatures (mp) Because ionic bonds are very strong, it takes much energy to break them Therefore, their mp’s are high

Sample mp’s of ionic compounds Compound Name Formula Unit mp (ºC) NaCl 801 (1473 F) MgO 2852 (5165 F) LiF 845 (1553 F) Sr(NO3)2 570 (1058 F) KNO3 334 (633 F)

Electrolytes Conduct electricity when dissolved or in a molten state Electrical current is a movement of charge Because ions are free to move in the molten or aqueous state

Electrolytes Substances that conduct electrical current when dissolved (aqueous state) Include ionic substances and some non-ionic (molecular) substances Strength of electrolyte corresponds to degree of dissociation or ion formation when in water

Electrolytes Strong electrolytes fully dissociate into ions when dissolved in water Weak electrolytes partially dissociate Non-electrolytes do not form ions when dissolved in water most non-ionic substances E.g. sugar (C12H22O11)

7.3 Bonding in Metals: Structure of Metals “Electron sea” model of metals valence electrons are free to move about in metals Metallic bonds: attraction between metal cations and core electrons of other cations

Metallic Bond Cations are attracted to electrons of other atoms Valence electrons are free to move from atom to atom

Properties of Metals are due to the Structure of Metals Ductility Malleability High electrical conductivity Luster High thermal conductivity Electron sea model of metals https://www.youtube.com/watch?v=c4udBSZfLHY

Compare Properties of Metals and Ionic Compounds Property Metals Ionic Compounds Malleability & ductility High Brittle Electrical conductivity as solid None Luster Low or none Thermal conductivity

Structure of Metals and Ionic Cpds Explains Their Different Properties

Crystal Structure of Metals Metal atoms arranged in orderly, compact patterns Unit Cell & Crystal Lattice

Alloys Homogeneous mixtures of which at least one component is a metal Alloys are examples of solid solutions Have superior properties to the pure metal, hardness, tensile strength, durability, etc.

Some bicycle frames are made of titanium alloys that contain aluminum and vanadium.

Steels are Alloys There are many alloys of steel used for different applications Vocational & Professional Opportunities… Metallurgy & metallurgical engineering Welding & welding engineering