Atomic trends

1. Atomic trends Mr.Yeung

2. How would you find the radius of these?

3. Atomic Radii • The atomic radius is the distance between two nuclei when two like atoms are bonded together. • In the figure above, the distance between the two nuclei in the molecule is 50 pm (1 pm = x 10−12m). • The atomic radius of the atom is then 25 pm.

4. Radii Decreases Radii increases

5. Atomic Radii Trends • Trends in atomic radius down a group • the atoms get bigger as you go down groups (moving to higher energy level). Adding more electrons, more shielding, electrons further away from nucleus, reducing forces • Trends in atomic radius across periods • atoms get smaller as you go across a period. • Adding proton  but still same energy level  shielding remains constant more force to pull on the electron  smaller atomic radius • Exclude the noble gas Shielding – Inner electrons tend to screen or shield the force of the nucleus from the outer electrons. So outer electrons can move further away.

6. Ionic Radii • Negative ions are larger • More electron – electron repulsion • Electrons outnumber protons, less forces on pulling the electrons in • Positive ions are smaller • Less electrons – less electron-electron repulsion  stronger forces pulling on the electrons • More protons  more forces

8. Ionization Energy What is it my master Splinter? Patience. Ionization energy is the amount of energy needed to remove an electron from a gaseous atom Like – A(g) + energy → A+(g) + 1e− Ahh… so what would affect the energy? Well, it depends on the force on the electron. The stronger the force, the more energy is required to remove the electron, the higher the ionization energy.

9. Well, since the atomic radii decreases as we go across the periodic table, would the ionization energy increase across since the atoms are smaller, and tighter? Yes! You are absolutely right. The distance between the nucleus and the outer electrons are closer together so they are held tighter making it more difficult to remove the electrons What about going down the periodic table? What do you think Ummm… since the atomic radii is increasing as we go down due to a new energy level and more shielding effect (as stated by He-Man), ummm I would think the energy required to remove the outer electron will decrease lowering the ionization energy Very well my young grass hopper. You are learning quickly

10. Yes, it seems like the numbers are getting bigger as more electrons are removed. But what does this mean? So the ionization energy increases as we go across the periodic table, and decreases going down the table. Is that all master Splinter? Ah my inquisitive student, it means the ionization energy increases as more electrons are removed. The more electrons you remove, the tighter the electrons are held. Some atoms can come in different ionic charges. What about the ones that have 1 electron removed, and then 2 and so on? Like this A+(g) → A2+ + 1e− Since you are removing electrons, the same number of protons will attract and hold the electrons tighter increasing the ionization energy Look at this table I made with my turtles. Do you see any patterns?

11. Is that all master? Look at this energy chart that I made. There is one thing left… The stable gases to the right. The Noble gases? Yes my son. They are very stable and do not like to be disturbed like a calm lake. When can you remove electrons from noble gases? Yes, because the outer valence electrons are removed, the next electrons that can be removed are in the lower energy level where the orbital is completely full. The electrons are also closer to the nucleus having a stronger hold with the nucleus. I see the ionization energy 2 went up dramatically! Is it because it is in the noble gas configuration since all the valence (outer) electrons are removed? What about Na+, or Al3+ Where they have removed enough electrons to achieve the noble gas configuration

12. Now is that all? Yes. You have done well my young grass hopper. I have provided you with a summary table for your atomic journey Thank you master

13. Atomic radius tends to decrease across a period and increase down a group. Ionic radius tends to decrease for every electron removed and increase for every electron added. • Ionization Energy • Ionization energy tends to increase across a period and decrease down a group. • Ionization energy tends to increase with each successive electron removed • Ionization energy tends to increase greatly when removing electrons from a noble gas configuration.