Atomic Structure and Periodic Trends

1. Atomic Structure and Periodic Trends Gabrielle Garcia Emily Surgeon

2. Valence Electrons & Electron Arrangement Valence Electrons equal to group # • Ex. How many valence electrons are in P? • Answer: 5 Electron arrangement: The way in which the shells of an atom are filled up/ arranged with electrons • 1st shell: 2; 2nd: 8; 3rd: 8 • Highest IB test will ask is Ca: 2,8,8,2 • Ex. What is the electron arrangement of Si? • Answer: 2, 8, 4

3. Atomic #, Mass #, & Isotopes • Atomic #: Number of protons/electrons in an atom • Mass #: Number of neutrons in an atom • Isotope: atoms that can have different mass # but same atomic # • Chemical properties of isotopes are the same • Physical properties are not Ex. What is the most common isotope of Nitrogen? • Answer: N 14

4. Calculating Average Atomic Mass • Average Atomic Mass: • %(mass1)+%(mass2)+... • Ex. Carbon • (12.000000) (0.9890) + (13.003355) (0.0110) = 12.011 amu

5. Mass Spectrometer • 1: Vaporization- element is heated until it’ s a gas • 2: Ionization- electrons are knocked off and it is turned into a positive ion • 3: Electric field- positive and negative, accelerates and focuses • 4: Magnetic field deflects, lightest ones get most deflection • 5: Detector- Mass is converted into abundance

7. Periodic Trends

8. Ionization Energy • The tendency of an atom to gain electrons in order to fill a shell • Increases across periods and up groups • Ex. Which has higher ionization energy, Antimony or Nitrogen? • Answer: Nitrogen • Why? • Antimony has more electron shells than Nitrogen, so its outer electron is shielded from the nucleus and experiences lower Zeff (effective nuclear charge) and is held more loosely. Thus, it is easier to remove an electron

9. Atomic Radii • Size of an atom • Decreases across periods, decreases down groups • Ex. Which has larger atomic radius: Francium or Radium? • Answer: Francium • Why? • Francium has less protons than Radium, but the same number of shells. So its outer electron experiences lower Zeff and is held more loosely. Thus it is a larger atom.

10. Ionic Radii • Size of an atom’s ion • Decreases across a period, increases down a group • Ex. Which has a larger ionic radius: Sodium or Sulfur? • Answer: Sulfur • Why? • Sodium has lost electrons and now has more protons than electrons, while Sulfur has gained electrons and now has more electrons than protons. So, the outer electrons in Sodium are held tighter by the protons (feels a higher Zeff) and its ion is smaller

11. Electronegativity • The tendency for an atom to attract electrons when forming an ionic bond • Increases across a period, increases up a group • Ex. Which has a higher electronegativity: Cesium or Lithium? • Answer: Lithium • Why? • Cesium has more electron shells than Lithium, so its outer electron is shielded from the nucleus (and experiences lower Zeff) and is held more loosely. Thus, it is pulling less on other electrons.

12. Melting Point • Temperature at which a solid element will melt • The stronger the forces that act between molecules of a substance, the higher the melting point tends to be. • Ex. Which has a higher melting point: Carbon or Sodium? • Answer: Carbon