HL Chemistry. Thursday August 20th Thursday, August 20, 15

Transcription

1 HL Chemistry Thursday August 20th 2015

2 Agenda Warm Up: Electron Configuration Practice Review Topic 2.2 Electron Configuration and begin Topic 12.1 Atomic Structure

3 Warm Up You have 10 minutes ONLY! GO! Work with a partner and answer the following questions: a) Deduce the full electron configuration for Mn and Mn 2+. b) Deduce the condensed electron configuration for Cu 2+. c) Draw orbital diagrams for Co 2+ and As.

4 Warm Up

5 HOMEWORK The Atom Project -Group Members? DUE August 31st 2015 No Exceptions! Energy of Waves (handout) DUE TODAY Questions? No Exceptions!

6 Electron Configuration Atomic orbitals An atomic orbital is a region in space where there is a high probability of finding an electron. Can hold a maximum of two electrons, with opposite spins Types of orbitals: s, p, d, f Each has a characteristic shape and associated energy

7 Electron Configuration The atomic orbitals Energy levels, sublevels, orbitals, and electron spin Energy levels are split into sublevels, which there are four common types: s, p, d, and f. Each sublevel contains a number of orbitals, each of which can hold a max of two electrons Sublevel Number of orbitals in sublevel Maximum number of e - in sublevel s 1 2 p 3 6 d 5 10 f 7 14

8 Electron Configuration Orbital diagrams Used to represent the electrons in these atomic orbitals. We will use these orbital diagrams to represent electron configurations!!! s sublevel (one box represents s orbital) p sublevel (three boxes represents the three p orbitals) d sublevel (five boxes represents the five d orbitals) f sublevel (seven boxes represents the seven f orbitals)

9 Electron Configuration Orbital diagrams Two electrons in same orbital will have opposite spin values of the spin magnetic quantum number, ms. The sign of ms (+1/2 or -1/2) indicates the orientation of the magnetic field generated by the electron. Electrons behave like two magnets facing opposite directions and is represented by two opposite arrows in a box. s sublevel (one box represents s orbital) p sublevel (three boxes represents the three p orbitals) d sublevel (five boxes represents the five d orbitals) f sublevel (seven boxes represents the seven f orbitals)

10 Electron Configuration Aufbau principle Electrons will fill from the lowest-energy orbital that is available first. Works up to Ca (Z=20) after that Sc (Z=21), the d orbital fills before the s and p orbitals since it is lower in energy. Electron configuration for Ca (Z=20) 1s 2, 2s 2, 2p 6, 3s 2, 3p 6, 4s 2 Electron configuration for Sc (Z=21) 1s 2, 2s 2, 2p 6, 3s 2, 3p 6, 3d 1, 4s 2 notice the d orbital is filled before the s orbital The Pauli Exclusion Principle states that any orbital can hold a maximum of two electrons, and these electrons have opposite spin. Hund s rule of maximum multiplicity states that when filling degenerate orbitals (orbitals of equal energy) electrons fill all the orbitals singly before occupying them in pairs. 2p

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12 Electron Configuration Condensed electron configuration Full electron configuration can get lengthy so scientists often write in condensed form: [nearest noble gas] + valence electrons Valence electrons are responsible for chemical reactions For example: [He] [He] 2s 2, 2p 4 [He] 2s 2, 2p 6 or simply [Ne] P [Ne] 3s 2, 3p 3 He O Ne

13 Electron Configuration Orbital diagrams Orbital diagrams uses the arrows in boxes notation Electrons are represented by arrows Boxes represent orbitals Degenerate orbitals are joined together to show their energy equivalence Can show full configuration or just from nearest noble gas Fluorine 1s 2, 2s 2, 2p 5 Energy 2s 2 2p 5 or [He] 2s 2 2p 5 This format will be on exam!!!! 1s 2

14 Topic 12.1 Electrons in atoms In an emission spectrum, the limit of convergence at higher frequency corresponds to the first ionization energy. Trends in first ionization energy across periods account for the existence of main energy levels and sub levels in atoms. Successive ionization energy data for an element give information that shows relations to electron configurations.

15 Electrons in atoms Nature of science Experimental evidence to support theories - emission spectra provide evidence for the existence of energy levels.

16 Electron Configuration Review Emission spectra and Bohr s theory of the hydrogen atom An electron can be excited to any energy level higher than its current level. They can also fall back down to any lower energy level. The difference in energy between the two energy levels can be expressed as follows Δ E = Ef - Ei hc = hv = λ

17 Electron Configuration Review Emission spectra and Bohr s theory of the hydrogen atom colour violet blue blue-green red λ/nm transition n = 6 n = 5 n = 4 to n = 2 n = 3 to n = 2 to to n = 2 n = 2

18 Electron Configuration Review Emission spectra and Bohr s theory of the hydrogen atom n=6 n=5 n=4 n=3 n=2 n=1

19 Electron Configuration Review Emission spectra and Bohr s theory of the hydrogen atom Series nf ni Region of EMS Lyman 1 2,3,4,5,... UV Balmer 2 3,4,5,6,... visible and UV Paschen 3 4,5,6,7,... IR

20 Electrons in atoms Emission spectra and ionization Emission spectra provide experimental evidence for the existence of atomic energy levels. Ionization energy is the minimum amount of energy required to remove an electron from a neutral gaseous atom or molecule in its ground state. First ionization energy (IE1): X(g) --> X + (g) + e - Second ionization energy (IE2): X(g) --> X 2+ (g) + e - Successive ionization energy (IEn): X (n-1)+ (g) --> X n+ (g) + e - With each successive ionization an electron is being removed from an increasingly positive species, so more energy is required. At higher energy, lines of spectra converge, forming a continuum. Outside of this limit the electron is no longer under the influence of the nucleus and has successfully been ionized.

21 Practice Problem... I Do... Determine the energy, in J, of a photon of red light, correct to four significant figures, given that the wavelength λ = 650.0nm. h = x J s; c = x 10 8 m s -1 E = hv = hc/λ E = [(6.626 x J s)(2.998 x 10 8 m s -1 )]/650.0 x 10-9 m E = x J

22 Practice Problem 15 mins... You Do... Work with a partner and answer the following question: Calculate the first ionization energy in kj mol-1, for hydrogen given that its shortest wavelength line in the Lyman series is 91.16nm. h = x J s; c = x 10 8 m s -1; NA = x mol -1 IE1 = 1312 kj mol -1

23 Electrons in atoms Ionization energies of first 20 elements Period 1 - Ionization energy increases Period 2 - Ionization energy increases

24 Electrons in atoms Ionization energies of first 20 elements Why is this? As the electrons are removed the nuclear charge increases across a period due to the increased attraction of the nucleus to the valence electrons! The atomic radius also decreases across a period making the electrostatic force even stronger! COOL!

25 Electrons in atoms Ionization energies of first 20 elements Group 1 - Ionization energy decreases Group 2 - Ionization energy decreases

26 Electrons in atoms Ionization energies of first 20 elements Why is this? As we move down a group, more energy levels are added and making the electrostatic force weaker as the distance between the nucleus and valence electrons increases - there is also an increase in electron shielding which further decreases the strength of the electrostatic force between the nucleus and valence electrons COOL!

27 Electrons in atoms Ionization energies of first 20 elements But WAIT! What about the discrepancies to the trend?

28 Electrons in atoms Exceptions to the trend Why is this? - Be has the electron configuration 1s 2 2s 2 - B has the electron configuration 1s 2 2s 2 2p 1 The electrons in the p orbital are higher in energy and further away from the nucleus and require less energy to remove than electrons in the s orbital - Mg has the electron configuration 1s 2 2s 2 2p 6 3s 2 - Al has the electron configuration 1s 2 2s 2 2p 6 3s 2 2p 1

29 Electrons in atoms Exceptions to the trend Why is this? - N has the electron configuration 1s 2 2s 2 2p 3 - O has the electron configuration 1s 2 2s 2 2p 4 Oxygen has a p orbital that is occupied by two electrons where nitrogen only has one electron in the p orbital. This means less energy is required to remove the electron in a half filled orbital due to the fact that like charges repel one another! P orbital Nitrogen P orbital Oxygen

30 Electrons in atoms Exceptions to the trend Why is this? More stable! Less stable! Orbitals that are empty, full, or half-full are more stable and require more energy to remove electrons!

31 Ionization Energy Trends in the Periodic Table of Elements Increasing ionization energy Increasing ionization energy

32 Topic 12.1 Electrons in atoms In an emission spectrum, the limit of convergence at higher frequency corresponds to the first ionization energy. Trends in first ionization energy across periods account for the existence of main energy levels and sub levels in atoms. Successive ionization energy data for an element give information that shows relations to electron configurations.

33 HOMEWORK The Atom Project -Group Members? DUE August 31st 2015 No Exceptions!