Section 3: Periodic Trends

Atomic Radius decreases Atomic Radius increases Periodic Trends Atomic Radius decreases Can you explain in terms of nuclear charge & shielding Atomic Radius increases

Atomic Radius decreases Atomic Radius increases Periodic Trends Atomic Radius decreases Ionization Energy ??? Electronegativity ??? Electronegativity ??? Ionization Energy ??? Atomic Radius increases

+ WHY? Ionization Energy (IE): energy required to remove an e– Down a Group: decreases ↓ Across a Period: WHY? increases ↑ Figure: 07-10 Title: First ionization energy versus atomic number. Caption: The red dots mark the beginning of a period (alkali metals), the blue dots mark the end of a period (noble gases), and the black dots indicate other representative elements. Green dots are used for the transition metals.

increases across a period First IE Trends + increases across a period -due to greater nuclear charge (more attraction) -due to more shielding (less attraction) decreases down a group

Example of Ionization Energy Trend Arrange in order of increasing first ionization energy: Mg, Na, Si, Al Na < Mg < Al < Si

Electronegativity (EN) Trends atom’s ability to attract bonded e–’s increases across a period -due to greater nuclear charge (more attraction) -due to more shielding (less attraction) decreases down a group

Example of Electronegativity Trend Arrange the following elements in order of increasing electronegativity: B, Na, F, O Na < B < O < F

Overall Reactivity Reactivity tells you how likely or vigorously atoms will react with each other. Trend for Metals: decreases across a period due to increased nuclear charge increases down a group due to more shielding

Overall Reactivity Reactivity tells you how likely or vigorously atoms will react with each other. Trend for Metals: The most reactive metals lose electrons the most easily (they are good electron donors)

Overall Reactivity Reactivity tells you how likely or vigorously atoms will react with each other. Trend for Non-Metals: increases across a period due to increased nuclear charge decreases down a group due to more shielding

Overall Reactivity Reactivity tells you how likely or vigorously atoms will react with each other. Trend for Non-Metals: The most reactive nonmetals gain electrons the most easily (they are good electron takers)

Overall Reactivity

Periodic Trends (Summary) Atomic Radius decreases Ionization Energy increases Electronegativity increases Can you explain all of this in terms of p’s and e’s? nuclear charge shielding Electronegativity decreases Ionization Energy decreases Atomic Radius increases

Quick Quiz! As you go across period 3 from Na to Ar, the energy needed to remove an electron from an atom ______________. A. decreases due to greater nuclear charge B. decreases due to less shielding C. increases due to greater nuclear charge D. increases due to less shielding

Quick Quiz. IE: 500 kJ 1500 kJ Alkali metals have lower ionization energies than noble gases because _____________. A. alkali metals are smaller with more protons. B. noble gases are larger with more protons. alkali metals are larger with lower nuclear charges. D. noble gases are smaller with fewer protons.

Quick Quiz. Fluorine is the most electronegative element because it has ____________. A. more nuclear charge and more shielding B. less nuclear charge and more shielding C. more nuclear charge and less shielding D. less nuclear charge and less shielding

Periodic Trends (Summary) Atomic Radius decreases Ionization Energy increases Electronegativity increases Can you explain all of this in terms of p’s and e’s? nuclear charge shielding Electronegativity decreases Ionization Energy decreases Atomic Radius increases