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Periodic Trends Barbara A. Gage PGCC CHM 1010
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Atomic Properties Depend on: – Number of protons – attractive nuclear force – Number of electrons – shielding effect of electron shells – Distance of electrons from nucleus – distance decreases nuclear force Barbara A. Gage PGCC CHM 1010
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Atomic Properties Atomic radius Barbara A. Gage PGCC CHM 1010 Metallic and covalent radii.
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Atomic Properties Click on image above to go to the Periodic Trends excelet Barbara A. Gage PGCC CHM 1010
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Ranking Elements by Atomic Size SOLUTION: PROBLEM:Using the periodic table, rank each set of main group elements in order of decreasing atomic size: (a) Ca, Mg, Sr(b) K, Ga, Ca(c) Br, Rb, Kr(d) Sr, Ca, Rb Elements in the same group increase in size and you go down; elements decrease in size as you go across a period. (a) Sr > Ca > MgThese elements are in Group 2A(2). (b) K > Ca > GaThese elements are in Period 4. (c) Rb > Br > KrRb has a higher energy level and is far to the left. Br is to the left of Kr. (d) Rb > Sr > CaCa is one energy level smaller than Rb and Sr. Rb is to the left of Sr.
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Atomic Properties Ionization energy energy required to remove an electron from a neutral, gaseous atom Cl (g) Cl 1+ + e - K (g) K 1+ + e - Barbara A. Gage PGCC CHM 1010
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First ionization energies of the main-group elements.
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Barbara A. Gage PGCC CHM 1010 Ranking Elements by First Ionization Energy SOLUTION: PROBLEM:Using the periodic table only, rank the elements in each of the following sets in order of decreasing IE 1 : (a) Kr, He, Ar(b) Sb, Te, Sn(c) K, Ca, Rb(d) I, Xe, Cs IE decreases as you proceed down in a group; IE increases as you go across a period. (a) He > Ar > Kr (b) Te > Sb > Sn (c) Ca > K > Rb (d) Xe > I > Cs Group 8A(18) - IE decreases down a group. Period 5 elements - IE increases across a period. Ca is to the right of K; Rb is below K. I is to the left of Xe; Cs is furtther to the left and down one period.
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Barbara A. Gage PGCC CHM 1010
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Atomic Properties Electron affinity energy change when an electron is added to a neutral atom to form a negative ion Cl + e - Cl - K + e - K 1- Barbara A. Gage PGCC CHM 1010
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Electron affinities of the main-group elements.
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Barbara A. Gage PGCC CHM 1010 Figure 8.15 and 8.16 Trends in four atomic properties.
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Ionic Properties Ionic radius radius of the ionic form of an atom Barbara A. Gage PGCC CHM 1010
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Ionic vs. atomic radii Cations
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Barbara A. Gage PGCC CHM 1010 Ionic vs. atomic radii Anions
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Barbara A. Gage PGCC CHM 1010 Ranking Ions by Size SOLUTION: PROBLEM:Rank each set of ions in order of decreasing size, and explain your ranking: (a) Ca 2+, Sr 2+, Mg 2+ (b) K +, S 2-, Cl - (c) Au +, Au 3+ Compare positions in the periodic table, formation of positive and negative ions and changes in size due to gain or loss of electrons. (a) Sr 2+ > Ca 2+ > Mg 2+ (b) S 2- > Cl - > K + These are members of the same Group (2A/2) and therefore decrease in size going up the group. The ions are isoelectronic; S 2- has the smallest Z eff and therefore is the largest while K + is a cation with a large Z eff and is the smallest. (c) Au + > Au 3+ The higher the + charge, the smaller the ion.
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