September 26, 2016 Chapter 1: Atomic Theory 1.2 The Periodic Table and Periodic Trends sBlock (Group 1 and 2): either have 1 valance elec1ron (Group 1: alkal2 metals) or 2 valence electrons (Group 2: alkaline earth metals). Group 1 have ns and group 2 has ns pBlock (Groups 1318): 13 has 3 VE, 14 has 4 VE, 15 has 5 VE Transition Elements: Groups 312 are known as the dblock elements. This block is 10 groups wide because the 5dorbitals hold a maximum of 10 electrons. Periodic Trends: The effective nuclear charge is defined as Z* = Z ( protons) Ncore( core electrons). It is the net positive charge experienced by the valence electrons when they are shielded by the core electrons from the full charge of the nucleus. From left to right, things get smaller because there are more protons, therefore more electrons being held more tightly because of the Z*. When you go from top to bottom, things get bigger because the of n increases, so the orbitals are getting better, making the electrons farther away from the nucleus. As Z* increases, the nuclear attraction between the atomic core and each of the valence electrons are pulled closer to the nucleus and the overall size of the atom decreases. Size of Atoms: the size of atoms is usually characterized by atomic radii and the size of ions are 12 characterized by ionic radii. These are normally expressed in picometers (pm), where 1pm = 1.0 x 10 . The larger the atom = the larger the bond. As one moves down a group, the size of the atoms. This is because atoms with a higher atomic have more electrons and they have to go somewhere so they occupy atomic orbitals with higher n numbers. Because d and f orbitals have poor shielding properties, the p electrons outside of d electron shell, do not have a good shield, so they are more attracted to the nucleus.