Atomic size, Ionization energy, Ionic size, & Electronegativity 14.2 – Periodic Trends Atomic size, Ionization energy, Ionic size, & Electronegativity

Atomic Radius Atomic radius = ½ the distance between the nuclei of diatomic molecules X-ray diffraction = a way to estimate the distance between nuclei of atoms to determine their relative size DNA

Trends (general) Group – size increases as you move down Periodic – size decreases as you move left to right

Ionization Energy The energy required to remove an electron from a gaseous atom First ionization = removal of 1st outermost e- Second ionization = removal of outermost e- from 1+ ion And so on… This concept is used to predict ionic charges.

Trends

Why is it more difficult to ionize the noble gases? Group IA

Ionic Size Ionic radii are the radii of the anions and cations in crystalline ionic compounds

Summary Radii generally decrease across the periods      Radii generally increase down the families      Cations are smaller and anions are larger than neutral atoms of the elements from which they are formed      Cations are generally smaller than anions      Effective nuclear charge increases across each period

Electronegativity Electronegativity is a measure of the tendency of an atom in a molecule or aggregate of atoms to attract electrons. Linus Pauling developed a scale of electronegativities so we use the Pauling as a unit

Summary: Electronegativity increases across the periods Electronegativity decreases down the families Trends are less regular for transition elements than for representative elements Metals have low electronegativities Fluorine and Oxygen are the two most electronegative elements Ionic bonds form between atoms of electronegativity difference of 1.7 or greater

Practice: How does the radius of an anion compare to the radius of a neutral atom for that element? Which element in each pair has a larger ionization energy: Na or K; Mg or P? For which of these properties does lithium have a larger value than potassium? 1st ionization energy, atomic radius, electronegativity, ionic radius?

Answers Anion is larger Na and P 1st ionization energy and electronegativity Check out this site: http://www.webteach.addr.com/CHSChemistry/periodic_table.htm