Periodic Trends. More than 20 properties change in predictable way based location of elements on PT

Transcription

1 Periodic Trends

2 Periodic Trends More than 20 properties change in predictable way based location of elements on PT Some properties: Density Melting point/boiling point Atomic radius Ionization energy Electronegativity

3 Going down group 1 Increasing # of energy levels... Period H Li Na K Rb Cs Fr Element Configuration

4 Increasing number of energy levels

5 Atomic Radius How large the radius is of an atom is what do you think influences that?

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7 Increasing number of energy levels Increasing Atomic Radius

8 Cs has more energy levels, so it s bigger next Li: Group 1 Period 2 Cs: Group 1 Period 6

9 As we go across, elements gain electrons, but they are getting smaller! Family Element Configuration IA or 1 Li 2-1 IIA or 2 Be 2-2 IIIA or 13 B 2-3 IVA or 14 C 2-4 VA or 15 N 2-5 VIA or 16 O 2-6 VIIA or 17 F 2-7 VIIIA or 18 Ne 2-8

10 Increasing Atomic Radius Increasing number of energy levels Decreasing Atomic Radius

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12 Ions and Atomic Radius What happens to the radius when an element becomes an ion? Anion = Cation =

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14 Electron Shielding This causes the net electrostatic force on electrons in outer shells to be significantly smaller in magnitude. Therefore, these electrons are not as strongly bound as electrons closer to the nucleus. This shielding effect explains why valence shell electrons are more easily removed from an atom.

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16 Why does this happen? As you go from left to right, you again more protons (the atomic number increases) You have greater proton pulling power Remember the nucleus is + and the electrons are - so they get pulled towards the nucleus The more protons your have, the more Proton Pulling Power

17 Ionization Energy Amount energy required to remove a valence electron from an atom in gas phase 1st ionization energy = energy required to remove the most loosely held valence electron (e - farthest from nucleus)

18 previous index next Cs valence electron lot farther away from nucleus than Li electrostatic attraction much weaker so easier to steal electron away from Cs THEREFORE, Li has a higher Ionization energy than Cs

19 Increased Ionization Energy (harder to remove an electron) Increased Electron Shielding Increasing Atomic Radius Increasing number of energy levels Decreasing Atomic Radius Decreased Ionization Energy (easier to remove an electron)

20 Electronegativity ability of atom to attract electrons in bond noble gases tend not to form bonds, so don t have electronegativity values Fluorine: most electronegative element = 4.0 Paulings

21 Decreased Ionization Energy (easier to remove an electron) Increased Electron Shielding Increasing Atomic Radius Increasing number of energy levels Decreased Electronegativity Increased Electronegativity Increased Ionization Energy (harder to remove an electron) Decreasing Atomic Radius

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23 Electronegativity ability of atom to attract electrons in bond noble gases tend not to form bonds, so don t have electronegativity values Fluorine: most electronegative element = 4.0 Paulings

24 DO NOW Draw the trends for: Electronegativity Ionization energy Atomic Radius Metallic Characteristic

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26 Valence Electrons An electron of an atom that is located in the outermost shell (valence shell) of an atom, that can be transferred to or shared to another atom.

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28 Lewis Dot Structure The valence electrons are shown as dots around the atom s symbol. These diagrams are an extremely useful model to help describe how atoms bond. To draw Lewis symbols for main groups of atoms: 1. Write the element symbol to represent the nucleus. 2. Add a dot to represent each valence electron. 3. Start by placing valence electrons singly into each of four valence orbitals (represented by the four sides of the element symbol).

29 Lewis Dot Structure F 2 CH 4 NH 3 BCl 3

30 DO NOW Draw lewis dot structures of the following: - Sulfur - Tin - HCl - NH 3