Chemistry 111 Chapter 8: Study Notes8.1 Development of the Periodic Table In 1864 the English chemist John Newlands noticed that when the known elementswere arranged in order of atomic mass, every eighth element had similar properties. Newlands referred to this peculiar relationship as the law of octaves. This turned out to be inadequate for elements beyond calcium, and Newlands work was not accepted by the community. Then in 1869 a Russian chemist named Dimitri Mendeleev tabulated the elements based on the regular, periodic recurrence of properties. First Mendeleev's classification grouped the elements together more accurately, according to their properties. Mendeleev proposed the existence of an unknown element that he called eka-aluminum.Using data from scattering experiments, Rutherford estimated the number of positive charges in the nucleus of a few elements, there was no general procedure for determining the atomic numbers. When high -energy electrons were focused on a target made of the elements studied X-rays were formed. The frequencies of the X-rays emitted from the elements could be correlated by the equation: v=a(Z-b) v is the frequency of the emitted X-ray and a and b are constants that are the same for all the elements.8.2 Periodic Classification of the ElementsRepresentative Elements ( also called main group elements) are the elements inGroups 1A through 7A which have incomplete;y filled s or p subshells of highest principal quantum number . With the exception of helium, the noble gases ( the Group 8A elements) all have a completely filled p subshell. The transition metals are elements in Groups 1B and 3B through 8B, which have completely filled d subshells. The Group 2B elements are Zn, Cd, and Hg, which are neither representative elements nor transition metals. The lanthanides and actinides are sometimes called f-block transition elements because they have incompletely filled f subshells.Group 1A alkali metals have similar outer electron configurations; each has a noblegas core and an ns configuration.. Group 2A alkaline earth metals have a noble gas core and an ns configuration of the outer electrons. The outer electrons of an atom , which are those involved in chemical bonding , are called valence electrons. The halogens (thegroup 7A elements), all with outer electron configurations of ns np, have similar propertiesas a group. The elements is Group 4A all have the same outer electron configuration ns np , but there is much chemical properties among these elements. The noble gases behave similarly. This is because all of the elements have completely filled outer ns and np subshells, a condition that represents great stability.The empirical formula are of course, the same as the symbols that represent the elements. Carbon , for example , exists as an extensive three-dimensional network of atoms, and so we use its empirical formula (C) to represent element carbon in chemical equations. All the noble gases exist as monatomic species ; thus we use their symbols: He, Ne, Ar, Kr, Xe, and Rn. The metalloids, like the metals , all exist in complex three-dimensional networks, and represents them , too, with their empirical formulas, that is, their symbols: B, Si, Ge, and so on.Ions Derived from Representative Elements.In the formation of a cation from the neutral atom of a representative element, one or more electrons are removed from the highest occupied n shell. Ions , or atoms and ions, that have the same number of electrons, and hence the same ground-state electron configuration are said to be isoelectronic.Cations Derived from Transition MetalsThe 4s orbital is always filled before the 3d orbitals. For example Manganese, whose electron configuration is [Ar] 4s 3d. When the Mn ion is formed, we might expect the two electrons to be removed from the 3d orbitals to yield [Ar]4s 3d. Actually the electronconfiguration is [Ar] 3d. The reason is that the electron-electron and electron-nucleus interactions in a neutral atom can be quite different from those in its ion. In forming a cation from an atom of a transition metal, electrons are always removed first from the ns orbital and then from the (n-1)d orbitals.8.3 Periodic Variation in Physical PropertiesEffective Nuclear ChargeThe presence of shielding electrons reduces the electrostatic attraction between thepositively charged protons in the nucleus and the outer electrons. The concept of effectivenuclear charge allows us to account for the effects of shielding on periodic properties. The effective nuclear charge, Zeff =Z-_where Z is the actual nuclear charge and (sigma ) is called the shielding constant ( also called the screening constant) Atomic RadiusThe electron density in an atom extends far beyond the nucleus. Several techniques allowus to estimate the size of an atom. First consider the metallic elements. Their atoms are linked to one another in an extensive three-dimensional network. The atomic radius is one- half the distance between the two nuclei in two adjacent metal atoms. For elementstat exist as simple diatomic molecules , the atomic radius is one-half the distance between the nuclei of the two atoms in a particular molecule.Ionic RadiusIonic radius is the radius of a cation or an anion. Ionic radius affects the physical and chemical properties of an ionic compound. When a neutral atom is converted to an ion, we expect a change in size. If the atom forms an anion, its size (or radius increases, since the nuclear charge remains the same but the repulsion resulting from the additional electron(s) enlarges the domain of the electron cloud.With isoelectronic cations, we see that the radii of tripositive ions( that is ions which have three positive charges) are smaller than those of dipositive ions ( that is ions that have twopositive charges, which in turn are smaller than unipositive ions ( that is , ions that have one positive charge). Variation of Physical Properties across a PeriodFrom left to right across a period, there is a transition from metals to metalloids to nonmetals. The molar heats of fusion and vaporization of a substance are the energies ( in kJ) needed to melt and vaporize on e mole of the substance at its melting point and boiling point, respectively. The terms "electrical conductivity" and thermal conductivity" are used qualitatively to indicate an elements ability to conduct electricity and heat. The electrical