Periodic Trends, Cont. Shielding Ion Size Ionization Energy Electronegativity Shielding Ion Size Ionization Energy Electronegativity

Chemistry Joke Q: What is a robber’s least favorite element? A: Copper!!!

Shielding The electrons in the outside energy level are blocked from the pull of the nucleus by all the inner electrons. The electrons in the outside energy level are blocked from the pull of the nucleus by all the inner electrons. The shielding does not change as you add electrons to the same energy level. The shielding does not change as you add electrons to the same energy level. The shielding increases when you move to the next highest energy level. The shielding increases when you move to the next highest energy level.

Shielding is constant Shielding increases ShieldingTrends Shielding Trends

Ion Size  To form ions, atoms may gain or lose electrons.  If an atom loses electrons, a positive ion is formed called a cation. – Metals tend to lose electrons.  This cation is smaller than the atom from which it formed. – It now has fewer occupied energy levels.

Ion Size  When an atom gains electrons, a negative ion is formed called an anion. – Nonmetals tend to gain electrons.  This anion is larger than the atom from which it was formed.  The period and group trends for ions are the same as atomic radius….except in the period trend when you cross the metal- nonmetal dividing line.

Ion Size Period Trend Li 1+ Be 2+ B 3+ C 4+ N 3- O 2- F 1- Cations—Atoms that have lost electrons to become positively charged. Smaller than the original, but showing the same trend in size. Anions—Atoms that have gained electrons to become negatively charged. Larger than the original, but showing the same trend in size.

Ionization Energy The amount of energy required to completely remove an electron from an atom. The amount of energy required to completely remove an electron from an atom. Removing one electron makes a +1 ion Removing one electron makes a +1 ion The energy required to remove the outermost electron is called the first ionization energy. The energy required to remove the outermost electron is called the first ionization energy. Also known as…IE Also known as…IE

Ionization Energy Trends As you go across a period… As you go across a period… The electrons are closer to the positive nucleus and therefore harder to pull off. The electrons are closer to the positive nucleus and therefore harder to pull off. The harder it is to pull off the electron, the higher the ionization energy. The harder it is to pull off the electron, the higher the ionization energy.

Ionization Energy Trends As you go down a group… As you go down a group… The electrons are farther away from the positive nucleus and therefore easier to pull off. The electrons are farther away from the positive nucleus and therefore easier to pull off. There are more electrons shielding the outer electrons from the positive nucleus, making them easier to pull off. There are more electrons shielding the outer electrons from the positive nucleus, making them easier to pull off. The easier it is to pull off the electron, the lower the ionization energy. The easier it is to pull off the electron, the lower the ionization energy.

Ionization Energy Trends Ionization Energy Trends (Generally) Increases Decreases

Ionization Energy Graph

Electronegativity The tendency for an atom to attract electrons to itself when it is chemically combined with another element. The tendency for an atom to attract electrons to itself when it is chemically combined with another element. Measures how fair an atom shares electrons. Measures how fair an atom shares electrons. Large electronegativity means it pulls the electron toward it strongly. Large electronegativity means it pulls the electron toward it strongly. Fluorine is the most electronegative element Fluorine is the most electronegative element

Electronegativity Trends Electronegativity Trends Increases Decreases Noble Gases are not electro- negative. F Fluorine is the most electronegative element.

Chemistry Joke Give this flask to Mel and tell him to put it away where no one can find it. What is it? It’s formaldehyde!!