4 1 Development of the Periodic Table Chapter 4 Chemistry Chemist John Newlands noticed that when elements were arranged in order of increasing atomic mass every eight element had similar properties Referred to this as the law of octaves TURNED OUT TO BE INADEQUATE after calcium Dmitri Mendeleev and Lothar Meyer proposed the phenomena of periodicity It grouped two elements together accurately according to their properties And it made it possible to pre dict the properties of several elements that had yet been discovered 4 2 The Modern Periodic Table periodic table is divided into the main group elements the noble gases the transition ele ments the lanthanides and the actinides main group elements representative elements are the elements group 1A through group 7A with the exception of helium noble gases group 8A have a completely filled p subshell transition metals group 1b 3b 3b 8b have incompletely filled d subshells lanthanides actinides are called the f block transition elements because they have in completely filled f subshells valence electrons the outermost electrons of an atom Determine how atoms interact with one another 4 3 Effective Nuclear Charge nuclear charge z is the number of protons in the nucleus of an atom effect nuclear charge Z eff is the actual magnitude of positive charge that is experienced by an electron in the atom shielding in an atom the electrons are simultaneously attracted to the nucleus and re pelled by one another 4 4 Periodic Trends in Properties of Elements the value of the principal quantum number increases as the distance from the nucleus in atomic radius the distance between the nucleus of an atom and its valence shell two ways in which the atomic radius is commonly defined as metallic radius covalent creases radius metallic radius is half the distance between the nuclei of two adjacent identical metal atoms covalent radius which is half the distance between the adjacent identical nuclei that are connected by a chemical bond the atomic radius decreases as we move from left to right across a period and increases from top to bottom as we moved down within a group ionization energy is the minimum energy required to remove an electron from an atom in the gas phase Results in an ion normally expressed in kj mol first ionization energy corresponds to the removal of the most loosely held electron from ion chemical species with a net charge each atom loss of one or more electrons yields a cation cation an ion with a net positive charge as effective nuclear charge increases so does ionization energy IE1 increases from left to right across a period and decreaes as we move from top to bottom within a group BUT group 3A has a lower ionization energy than that of Group 2A and Group 6A has a lower ionization energy than Group 5A ionization energy is an example of a chemical property and the process of ionization is a chemical process electron affinity is the energy released when an atom in the gas phases accepts an electron Increases from left to right across a period The EA of Group 2A is lower than the one for Group 1A and the EA of Group 5A elements is lower than that of Group 4A anion is an ion whose net charge is negative due to an increase in the number of electrons metallic character shiny lustrous malleable and ductile be good conductors of both heat and electricity have low ionization energies commonly form cations nonmetals vary in color and lack the shiny appearance associated with metals be brittle rather than malleable be poor conductors of both heat and electricity have high electron affinities metallic character increases from top to bottom i a group and decreases from left to right within a period metalloids elements with properties intermediate between those of metals and nonmetals diagonal relationship refers to similarities between pairs of elements in different groups and periods of the periodic table Normally due to charge densities of their cations 4 5 Electron Configurations of Ions group 1A and 2A charges of 1 and 2 Groups 4A Group 7A have charges corresponding to their group numbers minus 8 4 6 Ionic Radius ionic radius the radius of a cation or an anion affects the physical and chemical properties of the substance of which it is a part isoelectric series is a series of two or more species that have identical electron configura tions but different nuclear charges