K The Modern Periodic Table Part II: Periodic Trends November 13, 2014 ATOMIC RADIUS Period Trend *Across a period, Atomic Size DECREASES as Atomic Number INCREASES DECREASING SIZE Li Na K Rb Cs 2.2.0 1. 0 0 Group Trend *Within a group Atomic Size INCREASES as Atomic number INCREASES Trend In Classes of the Elements Across a Period Per Metals Metalloids Nonmetals 3 4 5 6 7 8 9 10 2 Li Be B C N O F Ne 11 12 13 14 15 16 17 18 3 Na Mg Al Si P S Cl Ar Trend in Ionic Radius Definition of Ion: An ion is a charged particle. Ions form from atoms when they gain or lose electrons. Trend in Ionic Radius v An ion that is formed when an atom gains electrons is negatively charged (anion) v Nonmetal ions form this way v Examples: Cl- , F- v An ion that is formed when an atom loses electrons is positively charged (cation) v Metal ions form this way v Examples: Al+3 , Li+ v METALS: The ATOM is larger than the ion v NON METALS: The ION is larger than atom Trends in Ionic Radii v In general, as you move left to right across a period the size of the positive ion decreases v As you move down a group the size of both positive and negative ions increase Ionization Energy Trends Definition: the energy required to remove an electron from a gaseous atom v The energy required to remove the first electron from an atom is its first ionization energy v The energy required to remove the second electron is its second ionization energy v Second and third ionization energies are always larger than the first Period Trend *Across a period, IONIZATION ENERGY increases from left to right Group Trend *Within a group, the IONIZATION ENERGY Decreases down a column Octet Rule Definition: Eight electrons in the outermost energy level (valence electrons) is a particularly stable arrangement. Atoms tend to gain, lose, or share electrons in order to acquire a full set of eight valence electrons. Octet Rule v Metals tend to lose electrons to obtain the noble gas arrangement v Metals have 3 or less valence electrons v Nonmetals tend to gain electrons to obtain this arrangement v Nonmetals have 5 or more valence electrons Trends in Electronegativity Definition - the relative ability of an atom to attract electrons to itself in a chemical bond v Electronegativity is a unitless value since it is a ratio of the same property for two elements Trends in Electronegativity *Across a period it INCREASES from left to right and within a group, electronegativity INCREASES up a group .