Chemical Periodicity Chapter 5 Periodic Trends in Atomic Size Periodic Trends in Ionization Energy Periodic Trends in Ionic Size Periodic Trends in Electronegativity

Periodic Trends in Atomic Size The boundary of an atom can't be measured directly Atomic Radius: half the distance between nuclei of two like atoms.

Write the Electron Configuration for Li, K and F Look at the position of these elements on the Periodic Table. Can you detect a “trend” in size as you go down a group? What do you think the trend is going across a period?

Periodic Trends in Atomic Size Atomic size increases down a group –What happens to the energy level as we go down a group? Where are the electrons? Atomic size decreases from left to right –Where are the electrons? –the nucleus has more attraction to the electrons

Periodic Trends in Atomic Size

Which would be bigger? a. Sodium or Aluminum b. Magnesium or Barium c. Nickel or Bromine d. Calcium or Yttrium e. Describe in your own words why atoms in the same period decrease in size from left to right.

Periodic Trends in Ionization Energy Ionization Energy: –Energy required to overcome the attraction of the nucleus and remove an electron.

Draw a Bohr model for Li, Na and N and F Ionization energy decreases as you move down a group because electrons are further away so they are easier to strip off. Ionization energy increases as you move left to right, for representative elements because the attraction by the nucleus is stronger so it is harder to pull electrons away.

Ionization Energy Graph Graph the data listed on the Table of ionization energies. Graph the Atomic number on the x-axis (1 thru 22) Graph the ionization energy on the y-axis (0 thru 160) What trend do you see?

Look at the Table of Ionization Energies First ionization energy- energy necessary to remove the 1 st electron Second ionization energy- energy necessary to remove the 2nd electron. Third ionization energy- energy necessary to remove the 3 rd electron.

Periodic Trends in Ionization Energy

Trends in Electron Affinity The energy change that occurs when an atom gains an electron. Let’s look at Li and F AGAIN Which one wants to gain an electron? It would have a high electron affinity

Electron Affinity-most atoms release energy when gaining an electron (explains the negative sign) Li kJ/mol Have to force the atom to take the electron. Energy absorbed Low affinity F -340 kJ/mol Gains electrons easily Energy is released High affinity

Trend in Electron Affinity

Periodic Trends in Ionic Size Let’s look at Li and F again. If each atom wants to achieve a full outer energy level (full octet)…. What has to happen to the electrons? When they gain or lose electrons, what do they become? What happens to the size of the atom?

Periodic Trends in Ionic Size Anions are atoms that have gained electrons and have an overall negative charge. Anions are larger than the atoms from which they have formed. Why?

Cations are atoms that have lost an electron and have an overall positive charge. Cations are smaller than the atom from which they have formed.

Check it out!

Periodic Trends in Ionic Size Cations decrease in the size from left to right. Anions decrease in size from left to right As you move down a group the radius increases because of more electrons in higher energy levels

Warm Up Which atom is the largest? Mg or Mg 2+ O or O 2- Cu 2+ or Cu 4+ Write a rule that will help you get these right every time!

Let’s go over some homework!

Isoelectronic Na 1+, Ne and F 1- are said to be Isoelectronic. Na 1+, Ne and F 1- are said to be Isoelectronic. a. Determine the electron configuration for each of the atoms b. Define isoelectronic

Isoelectronic 1. Write a 2- ion that is isoelectronic with Mg Write 3 ions that are isoelectronic with Kr 3. Write 2 ions that are isoelectonic with Ni

Trends in Electronegativity Electronegativity: –The tendency of an element to attract electrons when in a chemical bond. Let’s look at Li, Cs and F

Warm Up: In CB Which is more electronegative? Use the trend, then check them using the table. Al or Cl? Ca or Ba? Ga or S I or Cl? W or Zn?

Element Reactivity What would make an element reactive? Which elements are most reactive? What would make an element unreactive? Which elements would be most unreactive?

Let’s look at your table of electronegativities. Electronegativity table: –Noble gases are left out because they do not form compounds. –Metals have low electronegativity numbers because they want to give electrons away, not attract them. –Nonmetals have high electronegativity numbers because they attract electrons to make their configurations more stable

Trends in Electronegativity

Relationship Between Electronegativity and Ionization Energy Moving left to right, the representative elements, electronegativity increases because ionization energy increases Moving down a group electronegativity decreases because ionization energy decreases

Warm Up- Fill in the following table (p.159 may help) Atom Metal or nonmetal? Stable ion Size relative to neutral atom Larger or smaller than S 2- P Rb Cl Be Al

How did you do? Atom Metal or nonmetal? Stable ion Size relative to neutral atom Larger or smaller than S 2- Pnm P 3- largerlarger Rbm Rb 1+ smallersmaller Clnm Cl 1- largersmaller Bem Be 2+ smallersmaller Alm Al 3+ smallersmaller

Let’s practice some EC Al 3+ C 4-