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

2. 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

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

4. 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.

5. Trends

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

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

9. 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

11. 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

12. 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

14. 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?

15. Answers Anion is larger Na and P
1st ionization energy and electronegativity
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