1. Chapter 5
The Periodic Law

2. History
Cannizzaro- 1860
presented a new method for determining mass of elements
gave scientists a way to organize elements

3. History Mendeleev-Russian 1869
organized elements according to mass and properties
noticed that properties repeated periodically
predicted elements, later identified as Sc,Ga,Ge

4. History Moseley-1911 Used X-rays for determining the # of protons
This is how our current periodic table is arranged.

5. Periodic Law
Physical and chemical properties repeat periodically if arranged according to atomic number.
Recurring or reappearing from time to time; intermittent.
Look for overall patterns- may see some variation.

6. History Changes since Moseley Noble gases-Ramsay
Lanthanides/Actinides- Seaborg

8. The Periodic Table
Trends

9. Atomic Radius tells us the size of the atom
measured using ½ the distance between the nuclei of identical atoms bonded together

10. Atomic Radius TREND: going across the atoms get smaller
going down the atoms get larger

11. Ionic Radius tells us the size of the ion Cation-positive ion
positive or negative atom because of loss or gain of electrons
Cation-positive ion
Anion-negative ion

12. Ionic Radius
Cations are smaller than the parent
Lose electrons

13. Ionic Radius
Anions are larger than the parent.
Gain electrons.

14. Ion Formation Why do ions form? Atoms try to become stable.
Achieve a noble gas configuration.
Become isoelectronic with noble gases
Having the same electron configuration

15. Ion Formation
Examples:
Calcium
Nitrogen

16. Ion Formation
You try these:
Potassium
Iodine
Aluminum

17. Ionization Energy
Amount of energy required to remove an electron from an atom

18. Electron Affinity energy change when an electron is added to an atom
energy release means it is easier to add e-
opposite of ionization energy

19. Electronegativity
measure of the ability of an atom to attract electrons when it is bonded to another atom
Think: sharing with a partner, equal sharing or unequal sharing

20. Table of Electronegativities