Chapter 7 Ionic and Metallic Bonding 1 Section

Chapter 7 “Ionic and Metallic Bonding” 1

Section 7. 1 - Ions • OBJECTIVES: – Determine the number of valence electrons in an atom of a representative element. – Explain how the octet rule applies to atoms of metallic and nonmetallic elements. – Describe how cations form. – Explain how anions form. 2

Valence Electrons are… • The electrons responsible for the chemical properties of atoms, and are those in the outer energy level (or shell). • Valence electrons - electrons in the outer energy level or highest occupied energy level • Core electrons -those in the energy levels below. 3

Keeping Track of Electrons • Atoms in the same group. . . – Have the same outer electron configuration. – THUS …. . have the same valence electrons. • The number of valence electrons are easily determined: the group number for a representative element (groups #1, 2 & 13 thru 18) • Group 2: Be, Mg, Ca, etc. – have 2 valence electrons • Group 15: N, P, As, etc. – have 5 valence electrons 4

Electron Dot diagrams are… • A way of showing & keeping track of valence electrons. • How to write them? • Write the symbol - it represents the nucleus and inner (core) electrons • Put one dot for each valence electron (8 maximum) X 5

The Electron Dot diagram for Nitrogen: 5 valence electrons l First - write the symbol. l Next – add the 1 st & 2 nd electron to the 12 o’clock position l Next - More electrons are added to the 3 o’ clock, 6 o’ clock and 9 o’clock positions one at a time Any more electrons would pair up until there a max of 2 electrons to a side 6 l

The Octet Rule l l l Noble gases are unreactive in chemical reactions In 1916, Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and molecules The Octet Rule: in forming compounds, atoms tend to achieve a noble gas configuration; 8 in the outer level is stable l Each noble gas (except He) has 8 electrons in the outer level 7

Stable Electron Configurations • All atoms react to try and achieve a noble gas electron configuration. • Noble gases have 8 valence electrons = already stable! • This is the octet rule (8 in the outer level is particularly stable). Argon Electron Configuration: 2 -8 -8 It has 8 valence electrons Ar 8

Formation of Cations • Metals lose electrons to attain a noble gas configuration. • They make positive ions (cations) • If we look at the electron configuration, it makes sense to lose electrons: • Na 2 -8 -1 1 valence electron • Na 1+ 2 -8 This is a noble gas configuration (NEON) with 8 electrons in the outer level. 9

Electron Dots For Cations • Metals will have few valence electrons (usually 3 or less); calcium has only 2 valence electrons Ca Calcium Atom Electron Configuration: 2 -8 -8 -2 THUS 2 Valence Electrons 10

Electron Dots For Cations • Metals will lose the valence electrons to achieve a noble gas electron configuration (similar to Argon) Ca 11

Electron Dots For Cations • Thus … Metals will lose the valence electrons becoming positive ions or cations 2+ Ca This is named the calcium ion. NO DOTS are now shown for the cation. 12

Electron Configurations: Anions • Nonmetals gain electrons to attain a noble gas configuration. • They make negative ions (anions) • S = 2 -8 -6 = 6 valence electrons • S 2 - = 2 -8 -8 = noble gas configuration of Argon • Halide ions are ions from chlorine or other halogens that gain electrons 13

Electron Dots For Anions • Nonmetals will have many valence electrons (usually 5 or more) • They will gain electrons to achieve 8 electrons in its outer shell. P 3 P This is called the phosphide ion 14

Section 7. 2 Ionic Bonds and Ionic Compounds • OBJECTIVES: – Explain how atoms form an ionic compound. – Describe properties of ionic compounds. 15

Ionic Bonding • Anions and cations are held together by opposite charges forming a very strong bond. • Typically, metals combining with nonmetals to form a compound. • Ionic compounds are called salts. • The bond is formed through the transfer of electrons. • Electrons are transferred to achieve noble gas configuration for each atom in the compound. 16

Ionic Bonding Na Cl The metal (sodium) tends to lose its one electron from the outer level. The nonmetal (chlorine) needs to gain one more to fill its outer level, and will accept the one electron that sodium is 17 going to lose.

Ionic Bonding + Na Cl - Note: Remember that NO DOTS are now shown for the cation! 18

Ionic Bonding Lets do an example by combining calcium and phosphorus: Ca P • All the electrons must be accounted for, and each atom will have a noble gas configuration (which is stable). 19

Ionic Bonding Ca P 20

Ionic Bonding 2+ Ca P 21

Ionic Bonding 2+ Ca P Ca 22

Ionic Bonding 2+ Ca P 3 - Ca 23

Ionic Bonding 2+ Ca P 3 - 24

Ionic Bonding 2+ Ca P 3 - 25

Ionic Bonding Ca 2+ Ca P 3 - 26

Ionic Bonding Ca 2+ Ca P 3 - 27

Ionic Bonding 2+ Ca P 3 - P 328

Ionic Bonding = Ca 3 P 2 This is a chemical formula, which shows the kinds and numbers of atoms in the compound. 29

Properties of Ionic Compounds • Salts or Crystalline solids - a regular repeating arrangement of ions in the solid • Ionic bonds are very strong bonds Thus …… – Structure or crystal is rigid with – High melting points 30

Do they Conduct Electricity? • Electricity means movement of electrons or charges • In a solid, the ions (charged atoms) are locked in fixed position. • Thus as a solid – ionic compounds do not conduct electricity (insulators). 31

Do they Conduct? • However when melted or dissolved in water (aqueous) the ions are allowed to move around. • Therefore … they can conduct electricity 32

The ions are free to move when they are molten (melted) or dissolved in water (aqueous)), and thus they are able to conduct electric current. 33

Section 7. 3 Bonding in Metals • OBJECTIVES: – Explain the valence electrons of metal atoms. – Describe the arrangement of atoms in a metal. – Explain the importance of alloys. 34

Metallic Bonds are… • How metal atoms are held together in the solid. • Metals atoms lose valence electrons very easily • Think of them as different metal ions (cations) floating in a sea of electrons 35

Sea of Electrons • Electrons are free to move through the solid. • Thus…. Metals conduct electricity quite easily + + + 36

Metals are Malleable & Ductile • Malleable – can be hammered into sheets (bend). • Ductile – can be drawn into wires. • Both malleability and ductility are explained in terms of the mobility of the valence electrons 37

Due to the mobility of the valence electrons, metals have: 1) Ductility and 2) Malleability Notice that the ionic crystal breaks due to ion repulsion! 38

Malleable Force + + + 39

Malleable • Mobile electrons allow atoms to slide by, sort of like ball bearings in oil. Force + + + 40

On the other Hand…. . Ionic solids are brittle Force + + - + + 41

Ionic solids are brittle • Strong Repulsion between positive and negative ions breaks a crystal apart, (like charges repel) Force + + - + - + - + 42

Alloys • We use lots of metals every day, but very few are pure metals • Alloys are mixtures of 2 or more elements with at least 1 as a metal • made by melting a mixture of the ingredients, then cooling • Brass: an alloy of Cu and Zn • Bronze: an alloy of Cu and Sn 43

Why use alloys? • Properties are often superior to the pure element • EXAMPLE: Sterling silver (92. 5% Ag, 7. 5% Cu) is harder and more durable than pure Ag, but still soft enough to make jewelry and tableware • Steels are very important alloys – Mixture of Iron, carbon, Nickel, Molybdenum and other elements – corrosion resistant, ductility, hardness, toughness, cost 44

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