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Chapter 6 Atomic Radius, Section 5.15 Atomic Radius

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Chapter 6 Atomic Radius, Section 5.15 Atomic Radius Electron Configurations of Ions Chapter 6 z Anions: simply continue to add electrons in the Aufbau order Ionic Bonds and z Write the electron configuration of: - Periodic Trends z F z O2- z N3- z 1s2 2s2 2p6 for each z These ions are called isoelectronic. 1 2 Electron Configurations of Ions Electron Configurations of Ions z Cations: remove electrons in the reverse of z Transition metal cations: remove electrons the Aufbau order from the s orbital first, then in the reverse Aufbau order z Write the electron configuration of: z Write the electron configurations for: z Al3+ z Cr2+ z Mg2+ + z Na z Ti3+ z 1s2 2s2 2p6 z These ions are also isoelectronic. z Fe3+ z Problems 6.1, 6.2 3 4 Atomic Radius, Section 5.15 Atomic Radius Atomic Radii z Atomic radius can be predicted by looking at What trends do you notice elements’ numbers of electrons (left to right; z Definition: one-half the distance between two top to nucliitlei in two a djacen t a toms bottom)? Why? Problem 5.21 5 6 1 Effective Nuclear Charge Effective Trends in Atomic Radius Nuclear Charge z Electrons are all attracted to the nucleus, but z Which element in each pair has a larger electrons in inner shells shield protons and atomic radius? Why? reduce attractive forces of valence electrons. z F or Cl z The effec tive nuc lear c harge (Zeff)i) is the z C or N amount of positive charge from the nucleus z Rb or Ca that is perceived by an electron. z Na or Mg In a row (or period) in the Periodic Table, the number of protons increases, but the number of z K or Na inner e- (shielding e-) stays the same. Atoms on the right side of the Table can pull e- in more tightly. 7 8 Ionic Radius Trends in Ionic Radii z Radius of cation or anion z Which gets larger as it goes from atom to ion: cation or anion? Why? Ionic Radii In each pair, which is larger? Why? Zeff for Isoelectronic Series z In an isoelectronic series, all ions have the z Be2+ or B3+ same number of electrons, but the number of z Al3+ or P3- protons increases from most negative to most 2+ positive ion. z Ca or Ca z Therefore, the radius of the most positive ion is z K or Ca smallest and the most negative ion is largest. z O2- or F- z Place the following ions in order of increasing z Problem 6.3, 6.4 ionic radius: Cl1-, K1+, S2-, Ca2+, Al3+, P3- 12 2 Ionization Energy Periodicity of First Ionization Energy z Equation representing ionization energy: Ionize Trends X(g) → X+(g) + e- z Define ionization energy Mg Æ Mg+1 IE Defined 13 14 Trends in First Ionization Energy Electron Affinity z Which member of each pair has the larger z Equation representing electron affinity: - - first ionization energy? Why? X(g) + e → X (g) E- Affinity z F or Cl z Define electron affinity z N or C z Ionization energies are positive values (require z O or F input of energy). Electron affinities are negative for most atoms and for all cations. z Na or Mg z Greater attraction between atom and electron z K or Na results in more negative EA (e.g., halogens). z Worked Ex. 6.1; Problem 6.5 z Worked Ex. 6.3; Problem 6.10 15 16 Electron Affinity (kJ/mol) Octet Rule z Elements react in order to obtain 8 valence EA Trends (outermost) electrons. They do this by transferring electrons or sharing electrons. MtlMetals ten dtld to lose e lec trons (low IE)I.E.), nonme tltals tend to gain electrons (high E.A.). Nonmetal atoms donate electrons to metals to make ionic bonds. Both elements achieve an octet. Covalent bonds form when elements have to share electrons in order to get 8 valence electrons (an octet) (nonmetals + nonmetals). 17 3 2 The Ionic Bond Lattice Energy: F = k*(z1•z2 / d ) z What do the following have in common? z Lattice energy: energy required to completely LiF separate one mole of a solid ionic compound CaO into gaseous ions Mg3N2 z Look at Ionization Energies and Electron Affinities Low ionization energy Æ cations High electron affinity Æ anions 20 Relative Lattice Energies Relative Lattice Energies z Charges and sizes of ions determine the value z Which compound in each pair is more stable? of the lattice energy Is this determined by a high or low lattice z Larger lattice energy Æ more stable crystal Æ energy? Z+- Z stiibdtronger ionic bond NClNaCl or MClMgCl U=U = - A 2 d Charges are greater, or ± MgO or Na2O Sizes are smaller (lattice energy is inversely related NaCl or KCl to size) z Smaller radii Æ nuclei more strongly attracted to opposite NaBr or NaCl electrons z Worked Ex. 6.5 Æ z Problem 6.12, 6.13 21 22 Metals versus Nonmetals z Metals tend to react with water to form bases: CO2 (s) + H2O (l) Æ H2CO3 (aq) 2Na (s) + 2H2O Æ 2NaOH + H2 MgO (s) + H2O Æ Mg(OH)2 Alkali metals + water z Nonmetals tend to react with water to form acids: 2F2 (g) + 2H2O Æ 4HF + O2 CO2 (g) + H2O Æ H2CO3 4.
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