Ch. 6.3 Ions Ionic Bonding

POINT > Review ion basics POINT > Describe ionic bonds POINT > Distinguish between molecular formulas and formula units POINT > Describe the arrangement of ions in crystals POINT > Describe the properties of ionic compounds POINT > Define polyatomic ions

POINT > Review ion basics Valence electrons are electrons in the highest occupied energy level of an atom Number of valence e- is the same as Group number for main group elements (Groups 13-18 – Subtract 10)

POINT > Review ion basics Ca Ne Valence electrons determine chemical properties of the element Valence e- are the only electrons directly involved in chemical bonds Valence e- are shown by Electron Dot (Lewis) Structure diagrams

POINT > Review ion basics

Gilbert Lewis (1875 – 1946) POINT > Review ion basics Used stability of noble gases to explain why atoms form certain kind of ions & molecules Called explanation the Octet Rule

POINT > Review ion basics Octet rule: When forming compounds, atoms tend to achieve the electron configuration of a noble gas Configurations will end in ns2np6

POINT > Review ion basics Metals tend to lose valence e- to form positive charged cations Nonmetals tend to gain valence e- to form negative charged anions

POINT > Review ion basics Cation name matches that of the atom (a lithium atom forms a lithium cation) Cations are usually metals (atoms that have 1-3 valence electrons)

POINT > Review ion basics Mg 2e- Mg2+ +

POINT > Review ion basics Transition metals are less predictable: charges produced may vary Ex. Iron (Fe) often forms 2+ or 3+ cations Ex. Copper (Cu) forms 1+ or 2+ cations

POINT > Review ion basics The anion name differs from that of its atom, typically ending in –ide Ex. chlorine atoms form chloride anions sulfur atoms form sulfide anions oxygen atoms form oxide anions, etc

POINT > Review ion basics +

WB CHECK: Which would form an anion? strontium calcium aluminum sulfur chromium

WB CHECK: Which would form a cation? lithium potassium aluminum sulfur oxygen a-c d-e

POINT > Describe ionic bonds Ionic compounds are composed of metal cations & nonmetal anions Ionic compounds are electrically neutral as a whole, even though they are made of ions Positive charges must equal negative charges

POINT > Describe ionic bonds Ionic bonds result from electrostatic forces between ions of opposite charge The ions that form follow the octet rule

POINT > Distinguish between molecular formulas and formula units A chemical formula shows the numbers of atoms in the smallest representative unit of a substance Ex. H2O, C6H12O6, NaCl, MgBr2 For covalent compounds the unit is a molecule and the chemical formula is a molecular formula

POINT > Distinguish between molecular formulas and formula units Ionic compounds do not exist as discrete units Exist as a crystal lattice—not as discrete molecules

POINT > Distinguish between molecular formulas and formula units The formula unit is the lowest whole-number ratio of ions in an ionic compound (ex NaCl, CaCl2) For ionic compounds, chemical formulas are written as formula units because there is no discrete unit (the arrangement just repeats indefinitely)

WB CHECK: Which of these is a molecular formula? MgF2 SrO CF4 Li2S all of the above

WB CHECK: Which of these is a formula unit? CO2 CaCl2 CF4 SO2 all of the above

WB CHECK: Which of these is a chemical formula? CO2 CaCl2 CF4 SO2 all of the above

WB CHECK: The atoms in an ionic compound are held together by a) shared electrons b) differences in electronegativity c) electrostatic attraction d) electron affinity e) magic

POINT > Describe the arrangement of ions in crystals Most ionic compounds are crystalline solids at room temp Coordination number is the number of oppositely-charged ions that surround an ion of interest Each type of ion has its own number

POINT > Describe the arrangement of ions in crystals Coordination Number: Chloride is 6 Oxide is 3 Chloride is 8 Titanium is 6 Sodium is 6 Cesium is 8

POINT > Describe the properties of ionic compounds Ionic compounds have high melting & boiling points (compared to molecular compounds) Due to strong attractions between charged ions Good conductors when molten or dissolved in H2O Brittle (easily broken) because planes repel each other when dislocated

POINT > Define polyatomic ions A polyatomic ion: a charged group of covalently bonded atoms; e.g. NH4+ or CO32- Note the Lewis structures: brackets, charge shown, and number of electrons

Homework Read pages 180-184 F.A. page 184 #1-4