1.3 Periodic Trends 1) Metallic Character

2) Atomic Radius 3) Ionization Energy 4) Electron Affinity

METALLIC CHARACTER: how much an element behaves like a metal

Trend Across a PeriodMetallic Character decreases

Trend Down a GroupMetallic Character increases

Atomic Radiusthe distance from the center of an atom to the

outer valence shellHowever, the outer shell is a cloud, so really its the distance

between 2 nuclei of 2 atoms divided by 2.

atomic radius trend

3Li 4Be 5B 6C 7N 8O 9F 10Ne

Across a Period:

Effective nuclear charge (Zeff ) is the “positive charge” felt by an electron.

Atomic Radius Across a Period:As the number of protons in the nucleus increases, so does the effective nuclear charge, which causes electrons to be attracted to the nucleus, resulting in a smaller atomic radius.

The Reason for the Trend

3Lidown a group: 3Li

11Na

19K

37Rb

55Cs 11Na

19K

Atomic Radius increases down a group because there are more energy levels

IONIZATION ENERGY:the energy required to remove an electron from an atomhttp://www.youtube.com/watch?v=LxXqLzK9vmY

Trend Across a period: INCREASESBecause there are more protons (greater effective nuclear charge) increasing the attraction between the nucleus and the valence electrons. More energy is required to overcome this attraction.

Trend Going down a group: DECREASESBecause electrons in the outer level are further from the nucleus (weaker effective nuclear charge), less energy is needed to remove electrons from distant energy levels.

Electron Affinity

The energy absorbed or released when an electron is ADDED to a neutral atom

The electron affinities are expressed as negative values because energy is released in the formation of an ion.

As the values become more negative, the ions become more stable.

Trend: Across a Period: Electron Affinity increases (values are more negative) Why: Greater Effective Nuclear Charge increases the attraction of electrons to the nucleus

Down a Group : Electron Affinity decreasesWhy: Effective Nuclear Charge decreases because of the greater distance from the nucleus.

Question:The first I.E for Na is 495.9eVThe 2nd I.E. for Na is 4560 eVWhy is there a difference?

After Na loses its first electron it is isolectronic with the noble gas Neon. To lose a second electron would mean disrupting a stable ion; therefore the 2nd I.E is much higher.

Rearrange the following elements in order of Increasing Atomic Radius

F Li B

Rearrange the following elements in order of decreasing Atomic Radius

Br F Cl

F LiB

Br F Cl

Rearrange the following elements in order of increasing Ionization Energy

Na PAr Na P Ar

Rearrange the following elements in order of decreasing Ionization Energy

Br F Cl Br F Cl

Homework

Complete trends assignment and hand in. Pay attention to marking scheme on worksheet

Checkpoint 5: pg. 40 #2,,4,7,8,9