Periodic Trends (Day 2)

Today’s objectives LO 1.9 - The student is able to predict and/or justify trends in atomic properties based on location on the periodic table and/or the shell model. Students can make predictions about trends in electronegativity and first ionization energy.

Trend #2: Electronegativity What is it? Electronegativity is a property that specifically relates to covalent bonding (sharing of electrons). Electronegativity describes the attraction that an atom has for the shared electrons in a covalent bond. It’s a measure of how good an atom’s nucleus is at the “tug-of-war” for shared electrons.

Why is there no value for He, Ne, Ar, and Kr?

Examples Explain why magnesium has a higher electronegativity than strontium. Explain why chlorine has a higher electronegativity than silicon.

Explanation Across the period, electronegativity increases. All elements in a period have their valence electrons in the same energy level. Same # of shielding levels. The major difference is the increased effective nuclear charge as more protons are added to the nucleus. Down the group, electronegativty decreases. Elements in same group have same Zeff. Major difference is the shielding effect. More full energy levels between the nucleus and the valence electrons weaken the pull the nucleus has on those electrons.

Trend #3: Ionization Energy What is it? The amount of energy needed to remove an electron from the outermost shell. The higher the ionization energy, the harder it is to remove the electron. The “first ionization energy” refers to removing an electron from a neutral, gaseous atom. Ex. F (g)  F+ + e-

First Ionization Energy Plot

Explanation Across the period, 1st ionization energy increases. All elements in a period have their valence electrons in the same energy level. Same # of shielding levels. The major difference is the increased effective nuclear charge as more protons are added to the nucleus. Stronger pull from nucleus makes it more difficult (requiring more energy) to remove an electron. Down the group, 1st ionization energy decreases. Elements in same group have same Zeff. Major difference is the shielding effect. More full energy levels between the nucleus and the valence electrons weaken the pull the nucleus has on those electrons. Weaker pull from the nucleus makes it easier (requiring less energy) to remove an electron.