U NIT 3- REVIEW OF P ERIODIC P ROPERTIES OF THE E LEMENTS Elements in the same group (column) of the periodic table have the same number of electrons in their valence orbitals The chemistry of the elements differs due to atomic size, valence configuration, and electronic shielding effects The size of an atom may be gauged by its bonding atomic radius Atomic radii increase as we move down a column and decrease as we move from left to right across a row on the periodic table An isoelectronic series is a series of ions in which all the ions have the same number of electrons. In such a series, size decreases with increasing nuclear charge

2 Periodic Table of Elements

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The first ionization energy is the minimum energy required to remove an electron from the gas phase atom, forming a cation. First ionization energies show periodic trends that are opposite to those seen for atomic radii The electron affinity of an element is the energy change upon adding an electron to an atom in the gas phase, forming an anion. A negative electron affinity means that the anion is more stable than the neutral species and a positive electron affinity means that the anion is less stable and does not form easily

5 Ionization energy is the minimum energy (kJ/mol) required to remove an electron from a gaseous atom in its ground state. I 1 + X (g) X + (g) + e - I 2 + X + (g) X 2 + (g) + e - I 3 + X 2+ (g) X 3 + (g) + e - I 1 first ionization energy I 2 second ionization energy I 3 third ionization energy I 1 < I 2 < I 3

6 General Trends in First Ionization Energies Increasing First Ionization Energy

7 Filled n=1 shell Filled n=2 shell Filled n=3 shell Filled n=4 shell Filled n=5 shell Variation of the First Ionization Energy with Atomic Number

(a) Which atom should have a smaller first ionization energy: oxygen or sulfur? (b) Which atom should have a higher second ionization energy: lithium or beryllium? Do Now

P ROPERTIES Elements in the same group share certain properties: Alkali metals (group 1A): soft metals with low densities; they form 1+ cations Alkaline earth metals (group 2A): harder and more dense; they form 2+ cations Halogens (group 7A): nonmetals that exist as diatomic molecules; they form 1- anions Noble gases (group 8A): nonmetals that are unreactive in the ground state

C HEMISTRY OF C OORDINATION AND C OMPOUNDS Coordination compounds contain metal ions bonded to several surrounding ligands The number of donor ligand atoms attached to the central metal is the coordination number of the metal ion The most common coordination numbers are four (tetrahedral or square planar geometry) and six (octahedral coordination)

Many important coordination compounds are chelation compounds, such as porphyrins (chlorophylls, heme) and EDTA-containing complexes Coordination compounds can exhibit structural isomerism, linkage isomerism, and coordination- sphere isomerism, as well as stereoisomerism such as geometric isomerism and optical isomerism. Optical isomers or enantiomers are chiral. A substance has a particular color because it either (1) reflects or transmits light of that color or (2) absorbs light of a complementary color. The absorption spectrum is the amount of light absorbed by a sample as a function of wavelength