Periodic Trends

Li Na Li K Ne Ar

In the periodic table, vertical columns are called groups or families…

… while the horizontal rows are called periods.

Atomic Radius (AR) Make a QUICK sketch of this picture in the box. in the box.

Atomic Radius Across a period, atomic radius decreases. Reason: More protons pull on electrons which are in orbitals with similar energies.

Atomic Radius

Down a group, atomic radius increases. Reason: Elements have electrons in higher energy orbitals, which are farther from the nucleus.

The smallest radius is ______ while the largest radius is ________. The smallest radius is ______ while the largest radius is ________. Atomic Radius helium cesium(francium)

Rank the following from largest AR to smallest. 1) Br, Se, Ca 1) Br, Se, Ca Answer: Ca > Se > Br Answer: Ca > Se > Br Reason: Across a period radius ↓ Reason: Across a period radius ↓ 2) Be, Ca, Ba 2) Be, Ca, Ba Answer: Ba > Ca > Be Answer: Ba > Ca > Be Reason: Down a family, radius ↑ Reason: Down a family, radius ↑

Atomic Radius Atomic Radius Animation Atomic Radius Animation

Practice: 1. Arrange the following elements in order of increasing AR: Pb, Ba, Cs, At ___<___<___<___ 2. Arrange the following elements in order of decreasing AR: Be, Ba, Mg, Ra ___>___>___>___ At Pb Ba Cs Ra Ba Mg Be

Ion vs. Atom Size

Positive Ions Atom Size: Ion Size:

Positive Ions Positive ions are smaller than neutral atoms. Reason: There are the same number of protons pulling on fewer electrons.

Negative Ions Atom Size: Ion Size:

Negative Ions Negative ions are larger than neutral atoms. Reason: There are the same number of protons pulling on more electrons. ( More repulsion between electrons in electron cloud)

Practice:, H +1, and H -1 from largest to smallest AR: 1. Rank H, H +1, and H -1 from largest to smallest AR: H -1 > H > H +1 H -1 > H > H Which is larger: F -1 Ca or Ca +2, F or F -1 ? Ca > Ca +2 and F -1 > F

Ionic Radii Same trend as atoms, only with negative ions (anions) larger than positive ions (cations).

Practice: 1.Rank the following ions from smallest to largest: Cl -1, I -1, F -1 : F -1 < Cl -1 < I Rank the following ions from smallest to largest: Li +1, Cs +1, Na +1 : Li +1 < Na +1 < Cs Rank the following ions from smallest to largest: O -2, O -1, O : O < O -1 < O -2

Isoelectronic Series Animation

Isoelectronic Series An isoelectronic series contains atoms/ions with the same number of electrons. For example, Cl -1, Ar, and K +1 all have ______ electrons. When comparing the atomic radii in such a series, the key is to look at the number protons for each: The greater the number of protons pulling on the same number of electrons, the ______________ the radius. _______ > _______ > _______ Cl -1 Ar K +1 Cl -1 Ar K smaller

Practice: The two cations Na +1 and Al +3 are isoelectronic with what noble gas? ______. The ions both have ______ electrons, but Na has 11 protons and Al has 13 protons. Which ion will have the smaller AR and why? Ne Ne Al +3 will have a smaller AR because it has more protons

How much energy is required to remove an electron from an atom?

Ionization Energy (IE) ~ the energy required to remove an e -

What patterns do you notice across periods and down groups?

Ionization Energy

Ionization Energy (IE) ~ the energy required to remove an e - Across a period, ionization energy increases. Reason: Smaller atoms hold electrons more tightly (e - are closer to the nucleus). Link to electric hockey phet

Ionization Energy (IE) ~ the energy required to remove an e - Down a group, ionization energy decreases. Reason: Valence e - in larger atoms are farther from the nucleus. (e - are not as strongly attracted to nucleus).

Practice 1.Arrange the following elements in order of increasing IE: Pb, Ba, Cs, At Cs < Ba < Pb < At 2. Arrange the following elements in order of decreasing IE: Al, Na, S, Cl Na < Al < S < Cl