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Recap – Concentration

Recap – Concentration. Amount in moles, n = m / M. Many reactions occur in aqueous (water) solution Define the concentration in terms of number of moles in a litre of solution This is called molarity and has units mol L -1 or M. Concentration (molarity), c = n / V.

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Recap – Concentration

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  1. Recap – Concentration Amount in moles, n = m / M Many reactions occur in aqueous (water) solution Define the concentration in terms of number of moles in a litre of solution This is called molarity and has units mol L-1or M Concentration (molarity), c = n / V

  2. Recap - Atomic Emission Spectra • light emitted as an electron moves from a higher energy orbit to a lower energy orbit Energy n=6→n=2 n=5→n=2 n=4→n=2 n=3→n=2 n = 6 n = 5 n = 4 n = 3 n = 2 n = 1 H

  3. Recap - The Bohr Model • The number of electrons that can pack into an orbit depends on the size of the orbit.

  4. Problems with the Bohr Model • Periodic Table has blocks of elements: • “s block” (two elements wide) • “p block” (6 elements wide) • “d block” (10 elements wide) • “f block” (14 elements wide) • Rows are divided • second row: 2 + 6 • third row: 2 + 6 • fourth row: 2 + 10 + 6 p s d f

  5. Problems with the Bohr Model • Atomic emission spectra: H … more complex than expected from simple orbit model Si Mn Os

  6. Subshells • Each shell is divided into subshells called s, p, d, f…. • There is one extra subshell for each new shell • First shell: 1s • Second shell: 2s and 2p • Third shell: 3s, 3p and 3d • Fourth shell: 4s, 4p, 4d and 4f

  7. Filling Subshells • 2 electrons can fit into a s subshell • 6 electrons can fit into a psubshell • 10 electrons can fit into a dsubshell • 14 electrons can fit into a fsubshell energy increases energy increases

  8. s: 2 electrons p: 6 electrons d: 10 electrons Electron Configurations • Fill in order along diagonals • H has 1 electron: 1s1 • He has 2 electrons: 1s2 • Li has 3 electrons: 1s2 2s1 • Be has 4 electrons: 1s2 2s2 • B has 5 electrons: 1s2 2s2 2p1 (1s now full) (2s now full)

  9. s: 2 electrons p: 6 electrons d: 10 electrons Electron Configurations • Fill in order along diagonals • Ne has 10 electrons: 1s2 2s2 2p6 • Na has 11 electrons: 1s2 2s2 2p6 3s1 or:[Ne] 3s1 • Mg has 12 electrons: 1s2 2s2 2p6 3s2 or:[Ne] 3s2

  10. s: 2 electrons p: 6 electrons d: 10 electrons Electron Configurations • Fill in order along diagonals • Arhas 18 electrons: 1s2 2s2 2p6 3s2 3p6 • K has 19 electrons: 1s2 2s2 2p6 3s2 3p6 4s1 or:[Ar] 4s1 • Cahas 20 electrons: 1s2 2s2 2p6 3s2 3p6 4s1 or:[Ar] 4s2 Notice! We have filled 4s before 3d

  11. s: 2 electrons p: 6 electrons d: 10 electrons Excited Configurations • Electrons can be excited to higher energy levels • Ground state Na has 1s2 2s2 2p6 3s1 • One excited state of Na has 1s2 2s2 2p6 3s0 3p1 • Excited state relaxes to ground state emitting yellow light sodium line 1s2 2s2 2p6 3s0 3p1 The Sun 1s2 2s2 2p6 3s1 Na emission spectra sodium street light

  12. Periodic Table • Group 1: • Li: [He] 2s1 • Na: [Ne] 3s1 • K: [Ar] 4s1 • Group 2: • Be: [He] 2s2 • Mg: [Ne] 3s2 • Ca: [Ar] 4s2 • Elements in the same group have the samevalence electron configurations and, as a result, very similarchemical properties

  13. Learning Outcomes: By the end of this lecture, you should: understand the limitations of the Bohr model of the atom recognise that electron shells contain sub-shells recognise the connection between the Periodic Table and electron sub-shells know how the labels ‘s’, ‘p’ and ‘d’ relate to electron sub-shells and areas of the Periodic Table be able to write electron configurations of atoms and ions be able to complete the worksheet (if you haven’t already done so…)

  14. Questions to complete for next lecture: • List the sub-shells present in the third shell and indicate the maximum number of electrons each may contain. • Write the electron configuration of the following atoms or ions: • N • P3- • Ca • Fe • What feature do all elements in the ‘p’ – block of the Periodic Table share?

  15. Questions to complete for next lecture: • The electron configuration of He is 1s2. Why do you think it is included in Group 18 in the Periodic Table rather than Group 2? • Which of the following are impossible electron configurations? Give your reason(s). • 1s2 2p1 • 1s2 2s3 • 1s2 2s2 2p6 3d1 • 1s2 2s2 2p7 • 1s2 2s0.5

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