Drill – 11/19 What is meant by “periodic trend”?

Periodic Trends

Nuclear Charge Nuclear charge-the charge in the nucleus or the number of protons Across – increases Down – increases

Valence Electrons The electrons in the outermost energy level (s and p orbitals only!) Across – increase Na Mg Al Si … Ar 3s1 3s2 3s23p1 3s23p2 …3s23p6 1 2 3 4 ... 8

Valence Electrons The electrons in the outer most energy level (s and p orbitals only!) Down – stays the same. This is why there are trends in reactivity for families Be Mg Ca Sr 2s2 3s2 4s2 5s2 2 2 2 2

Atomic Mass Weighted average (based on mass and percent abundance of each naturally occurring isotope) Across – increases Down – increases Remember there are some exceptions to this – like Te and I

Shielding Effect The shielding effect is the reduction of attractive force between the nucleus (+) and its outer electrons (-) due to the blocking affect of the inner electrons Nucleus Shielding electrons Valence electrons ‘shielded’ by inner electrons

Shielding Effect Across – stays the same Electrons are added in the Valence shell and the shielding electrons remain the same

Shielding Effect Down – increases Another layer of electrons is added and the shielding between the valence shell and the nucleus increases

Atomic Radius One half the distance from center to center of like atoms 1/2

Atomic Radius Across – decreases As the number of p+ in the nucleus and e- in the valence shell increases, the nucleus exerts a greater pull on all of the electrons

Atomic Radius Down – increases A new energy level is added increasing the size of the atoms

Ionization energy The amount of energy needed to remove an electron 1st Ionization Energy – energy needed to remove the 1st e- from an atom + Ionization Energy + + e-

Ionization Energy Across – increases e- are more strongly attracted to nucleus, increasing the energy necessary to remove an e-

Ionization Energy Down – Decreases e- are further from the nucleus. Less energy is needed to remove an electron.

Ionic Radius Radius of an ion -- the size of an ion is different than the size of the atom it came from. If an atom loses an e- then it will have a pos. charge and is called a CATION. If an atom gains an e- then it will have a neg. charge and is called an ANION.

Ionic Radius Cations will be smaller than the original atom. This is due to a stronger nuclear pull. Anions will be larger than the original atom. The additional e- goes into the same energy level and the e- will repel each other and spread out.

Electronegativity The tendency for an atom to attract electrons in a bond.

Electronegativity Across – Increases Stronger nuclei have greater nuclear pull for e-.

Electronegativity Down – Decreases Larger atoms have less pull on e-.

Electron Affinity The energy change when an electron is added to a neutral atom to form a negative ion Higher e- affinity = easier to add an e- = stronger nucleus

Trends Across the Periodic Table Shielding Effect Stays the Same Atomic Radius decreases Ionization Energy Increases Electronegativity Increases Electron Affinity Increases

Trends Down the Periodic Table Shielding Effect Increases Atomic Radius Increases Ionization Energy Decreases Electronegativity Decreases Electron Affinity Decreases