Slide 1 / 102 Slide 2 / 102 New Jersey Center for Teaching and Learning Progressive Science Initiative AP Chemistry This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to Periodic Trends make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website: www.njctl.org www.njctl.org Slide 3 / 102 Slide 4 / 102 The Periodic Law The Periodic Law Over the course of this unit, we will use our knowledge of the atom to explain the periodic trends we see regarding the following properties: PROPERTY DEFINITION Ionic Charge charge of common ion formed by that element Atomic/Ionic Radii Distance from the nucleus to outermost electron Density Ratio of Mass/Volume Ionization Energy Energy required to remove valence electron Recall that the periodic law states that the physical and chemical Disposition to have metallic characteristics - ie. conduct Metallic Character properties of the elements tend to recur in a systematic way when electricity arranged by increasing atomic number. Measure of attraction for electrons when the atom is Electronegativity sharing electrons in a molecule. Slide 5 / 102 Slide 6 / 102 The Periodic Law The Periodic Law Recall that the periodic law states that the physical and chemical The pattern can be easily visualized on a graph, particularly as we properties of the elements tend to recur in a systematic way when move past the first 11 elements! arranged by increasing atomic number. Let's look at the first eleven elements to illustrate this. +4 +3 ion H He Li Be B C N O F Ne Na charge Atomic +2 1 2 3 4 5 6 7 8 9 10 11 Number +1 Ionic +1,-1 NA +1 +2 +3 +4 -3 -2 -1 NA +1 Charges 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 -1 atomic number Notice that neither He or Ne form ions. Also, notice that in -2 both cases the atom that precedes them can form a -1 ion and the atom that succeeds them forms a +1 ion. -3 There is definitely a systemic pattern here!
Slide 7 / 102 Slide 8 / 102 The Periodic Law and the Quantum Model The Periodic Law and the Quantum Model This trend in ionic charge can be easily explained if we apply the Let's use to quantum model to answer some questions quantum model of the atom. about these ionic charges. Principal Quantum Question 1: Why do both He and Ne not form ions? Lose/ Electron Ionic Element Number (N) Gain Configuration Charge of valence electrons Both have a full principal energy level electrons gain 1 -1 H 1 1s 1 move for answer He = 1s 2 The pattern recurs with lose 1 +1 every increase in the He 1 1s 2 NA NA Ne = [He]2s 2 2p 6 Li 2 [He]2s 1 lose 1 +1 principal quantum Be 2 [He]2s 2 lose 2 +2 number. This means Question 2: Why do both Li and Na have the same charge? B 2 [He]2s 2 2p 1 lose 3 +3 every time a new shell C 2 [He]2s 2 2p 2 lose 4 +4 of electrons is filled, the Both require only a small amount of energy to lose 1 electron to pattern repeats! become a noble gas with a full principal energy level. N 2 [He]2s 2 2p 3 gain 3 -3 move for answer O 2 [He]2s 2 2p 4 gain 2 -2 F 2 [He]2s 2 2p 5 gain 1 -1 Ne 2 [He]2s 2 2p 6 NA NA Na 3 [Ne]3s 1 lose 1 +1 Slide 9 / 102 Slide 10 / 102 The Periodic Law and the Quantum Model The Periodic Law and the Quantum Model Question 3: Explain why P would be expected to have the same ionic We have seen that the quantum model explains the periodic charge as N? trend with regard to ionic charges for the main group elements in the first three periods. Both have the same number of valence electrons (5) so both need to gain three electrons to fill their outer principal energy level. move for answer N = [He]2s 2 2p 3 gain 3 e- --> Ne Quantum theory can also explain the periodic trends amongst the transition elements that are in the midst of filling their "d" orbitals. P = [Ne]3s 2 3p 3 gain 3 e- --> Ar Question 4: After sodium, which element would most likely form an ion with +1 charge and why? d orbital Potassium (K), because it is beginning to fill the 4th principal +3 +4 +5 +6 +7 +3 +3 +2 +1 +2 energy level with 1 electron, just as sodium was beginning the move for answer +3 +4 +5 +6 +7 +3 +3 +2 +1 +2 3rd with 1 electron. transition elements Slide 11 / 102 Slide 12 / 102 The Periodic Law and the Quantum Model The Periodic Law and the Quantum Model Let's use quantum theory to explain the trends we see amongst the charges of the transition elements. d orbital +3 +4 +5 +6 +7 +3 +3 +2 +1 +2 +4 +5 +3 +6 +7 +3 +3 +2 +1 +2 Question 1: Elements within the Fe group can form ions of both +2 and +3 charges. Explain why the +3 charge is more common: Fe = [Ar]4s 2 3d 6 transition elements The 4s electrons are readily lost yielding the +2 ion. move for answer The charges increase from left to right as the atoms lose both A half-full "d" orbital is quite stable so Fe will lose 1 d orbital their two valence "s" electrons and however many "d" electrons electron as well to yield the +3 ion. they have also. After the Mn group, the charges decrease, one of the reasons being that the stability of the "d" orbital increases as it becomes full.
Slide 13 / 102 Slide 14 / 102 1 The trends in chemical and physical properties tend The Periodic Law and the Quantum Model to recur as atoms… Let's use quantum theory to explain the trends we see among the charges of the transition elements. A Fill a new principal energy level B Gain more neutrons Answer Question 2: Why do the elements in the zinc group tend to only form ions with a +2 charge? C Decrease in mass Zn = [Ar]4s 2 3d 10 D Increase in atomic number move for answer The "d" orbital is full so only the outer "s" electrons are lost. E Both A and D Slide 15 / 102 Slide 16 / 102 2 An atom with a +2 charge must be in the same group 3 Which of the following BEST explains why O and S as barium. both form ions with a -2 charge? True A They both have the same atomic number False B They are both in the same period Answer C They both have the same electron configuration Answer D They both have the same number of valence electrons E They both have the same mass Slide 17 / 102 Slide 18 / 102 4 An atom with the electron configuration of [Kr]5s 2 4d 2 5 Atoms on the right side of the chart tend to form would be in the same group as _____ and have a negative ions because... likely charge of ____. A Their principal energy level is almost empty A Sc, +1 B Their principal energy level is almost full Answer B Hf, +4 Answer C Their atomic number is less than other elements in C Ti, +3 that period D Zn, +2 D Both B and C E Y, +1 E A, B, and C
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