2Homeworkp #3-11, p # 31-32, 35-40, 55-56, 58-59, 62-63, 65 – DUE WEDNESDAYp. 199 # 16, 18-20, p # 42,45 – DUE THURSDAYQuiz over Table 7.2 on Wends, Nov 9Test over Ch. 7 on Tuesday, Nov. 15 (tentative)
3Review1. What is an ion?ion – an atom with a positive or negative charge (an electron has been lost or gained)2. Where on the periodic table are the metals located? Nonmetals?
4Valence ElectronsCore Electrons – “inner” electrons, do not participate in bondingValence Electrons – “outer” electrons, electrons in the highest occupied energy levelnumber of valence electrons largely determines the chemical properties of an elementSo which electrons in an electron configuration are core and valence?Be – [He] 2s2 P – [Ne] 3s2 3p3Core Valence Core Valence
5So how do I find this valence number? The valence electrons an atom has is the same as its group number for a representative (main group) element
6So how do I find this valence number? So how many valence electrons would Na have?1Iodine?7Krypton?8
7How do I keep track of all these valence electrons? Valence electrons are VERY important for chemistry and reactions!Why?Chemists have electron dot structures – diagrams that show valence electrons as dots
8How do I keep track of all these valence electrons? What do you notice about valence electrons down a group?Electron configuration remains the same down a group, only the core electrons change
9PracticeHow many valence electrons does Al have? Draw the Lewis dot structure.Electron configuration:Valence Electrons:Lewis dot structure:[Ne] 3s2 3s13
10Crystal StructuresIn crystalline materials, elements repeat in repetition to give a 3D arrangement known as a crystal latticeA unit cell is the smallest part of the lattice that represents the entire lattice (repeated part)4 types of unit cells:PrimitiveBody-centeredFace-centeredHexagonal close-packed
12Part I: MetalsCrystal coordination number (CN): number of neighbors to an atom in a unit cellExample: simple cubic is 6
13Part I: MetalsCrystal coordination number (CN): number of neighbors to an atom in a unit cellFace-centered:12Body-Centered:8Hexagonal:
14Let’s Think!We know noble gases are very stable. How can we get the other elements to become stable like the noble gases?Hint: Think of valence electrons!
15Octet Rule All elements want eight valence electrons (except H and He) Why?Achieve noble gas configuration, most STABLE2 electrons come from the s subshell and 6 from the p subshellWhy can H and He NOT have eight valence electrons (Hint: they are considered stable with TWO valence electrons)No p subshell!
16Octet RuleElements will tend to gain or lose enough electrons to fulfill their octetWill metallic elements gain or lose electrons?Lose, much easier to lose electrons than gain electronsWill nonmetallic elements gains or lose electrons?Gain, much easier to gain electrons (can also share electrons)
17Octet Rule Metallic elements lose electrons Why?In simple terms…easier to lose than to gain to form the octetNonmetallic elements gain electronsIn simple terms, easier to gain a few electrons than lose themNow let’s consider periodic trends!Nuclear attraction across:Shielding effect across:Kinetic energy across:This means:Increases across, nonmetals held tighter than metalsRemains constant, does not offset nuclear attractionRemains constantMetals hold onto their electrons less tightly so it is easier for metals to lose their electrons. Additionally, nonmetals hold onto their electrons tighter . This trend, and the fact that nonmetals have higher electron affinity, means nonmetals tend to gain electrons.
18Octet RuleIf metals lose electrons, they will form ions. Will these ions be negatively or positively charged?If nonmetals gain electrons, will their ions be negatively or positively charged?
19Octet RuleIons get special names to distinguish between those ions that are positively charged and those that are negatively chargedCation – positively charged ionLet’s try sodium!Electron configuration:Original electron dot diagram:How many electrons will it lose?New electron dot diagram:New electron configuration[Ne] 3s11Na+[Ne]
20Octet RuleIons get special names to distinguish between those ions that are positively charged and those that are negatively chargedCation – positively charged ion
21Octet Rule - CationsIons get special names to distinguish between those ions that are positively charged and those that are negatively chargedCation – positively charged ion
22I wonder…Mg has the electron configuration of [Ne] 3s2. How many electrons would it lose or gain stability?2Will it take more or less energy to remove the second electron than the first electron?Let’s use electron dot structures to show its loss of 2e-
23Octet Rule - CationsWe just did one example of formation of a cation from Group 1 and Group 2. What can we say about the general formation of cations from Group 1 and the general fromation of cations from Group 2?Group 1 – form +1 cationGroup 2 – form + 2 cation
24What about those transition metals? It’s extremely hard for transition metals to lose enough electrons to form a noble gas configuration. Why?They would have to lose all the s and d electrons!The transition metals ending with ns1(n-1)d10 can lose that 1s electron to achieve pseudo noble-gas electron configurationWhat is one element that does this?Elements with the configuration ns1(n-1)d5 can also lose that 1s electron to achieve half shell stabilityWhat is one element that can do this?
26Octet Rule - AnionsIons get special names to distinguish between those ions that are positively charged and those that are negatively chargedAnion – negatively charged ionLet’s try chlorine!Electron configuration:Electron diagram:How many electrons will it gain?New electron diagram:New electron configuration[Ne]3s2 3p51Cl-[Ne]3s2 3p6
27Octet Rule - AnionsIons get special names to distinguish between those ions that are positively charged and those that are negatively chargedAnion – negatively charged ion
28Octet Rule - AnionsIons get special names to distinguish between those ions that are positively charged and those that are negatively chargedAnion – negatively charged ion
29I wonder…O has the electron configuration of [He] 2s2 2p4. How many electrons would it gain to gain stability?2Will it take more or less energy to gain the second electron than the first electron?Let’s use electron dot structures to show its gain of 2e-
30Octet Rule - AnionsHow many electrons need to be gained by each group in group 5,6, and 7 to be stable?
34Let’s Think!We all know that certain elements will bond together to form molecules, such as NaCl (table salt). Why is this?Hint: Think of valence electrons.
35Ionic BondingIonic compound – composed of metal cations and nonmetal anionsThey are still electrically neutralWhy?The charges of the cation and anion cancel outThe negatively charged anion and the positively charged cation attract each other by electrostatic forces (force holding a cation and anion together due to their charge)
36Ionic BondingIonic compound – composed of metal cations and nonmetal anionsLet’s go back to the formation of NaCl…What’s the electron configuration of Na?Of Cl?Their valence electrons can “add” together to form an ionic compound…now both elements are happy…just like Justin and Selena![Ne] 3s1[Ne] 3s2 3p5
37Ionic BondingIonic compound – composed of metal cations and nonmetal anions
38Ionic BondingIonic compound – composed of metal cations and nonmetal anions
39Ionic BondingIonic compound – composed of metal cations and nonmetal anions
40Ionic Bonding So Na+ and Cl- combine to form NaCl NaCl is the chemical formula or a way to show the kinds and numbers of atoms in the smallest unit of a substanceSo there is 1 Na+ for every 1 Cl-What would Mg+2 and Cl-1 form?There is 1 Mg+2 for every 2 Cl-1 so MgCl2Think of it this way: the charges have to become neutral
41Ionic Bonding The charges must become neutral What about Sr+2 and F-? SrF2
42Ionic Bonding Another way to do it is balance out the charges Ex: 1 Mg has a +2 charge and 1 O has a -2 charge. The charges are already balanced!So we have….MgOWhat about….1 Be has a +2 charge and 1 Br has a -1 charge.How many Br will be needed to balance out the charges?2…so that gives us….BeBr2