2016 Trends and nuclear charge.notebook

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February 17, 2016

TRENDS IN THE PERIODIC TABLE 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

Trend Down a GroupMetallic Character

decreases

increases

Atomic Radiusthe distance from the center of an atom to the

outer valence shell

However, the outer shell is a cloud, so really its the distance between 2 nuclei of 2 atoms divided by 2.

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

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

Across a Period: ATOMIC RADIUS DECREASES

Li C F

2016 Trends and nuclear charge.notebook

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February 17, 2016

3Lidown a group:

3Li

11Na

19K

37Rb

55Cs

11Na

19K

Atomic Radius increases

because there are more energy levels

atomic radius trend

IONIZATION ENERGY:the energy required to remove an electron from an atomwatch

Trend Across a period: Because 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: Because 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.

INCREASES

DECREASES

2016 Trends and nuclear charge.notebook

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February 17, 2016

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

Ne Li B

Rearrange the following elements in order of decreasing Atomic Radius

Br F Cl

Ne 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

Electron Affinity

The energy 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 attractions to the nucleus

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