1. The Periodic Law
Dimitri Mendeleev was the first scientist to publish an organized periodic table of the known elements.
He was perpetually in trouble with the Russian government and the Russian Orthodox Church, but he was brilliant never-the-less.

2. The Periodic Law
Mendeleev even went out on a limb and predicted the properties of 2 at the time undiscovered elements.
Mendeleev, for instance, predicted the discovery of germanium (which he called eka-silicon) as an element with an atomic weight between that of zinc and arsenic, but with chemical properties similar to those of silicon.

3. Mendeleev, for instance, predicted the discovery of germanium (which he called eka-silicon) as an element with an atomic weight between that of zinc and arsenic, but with chemical properties similar to those of silicon. (Same properties = Same group/Family = 4A)

4. The Periodic Law Mendeleev understood the ‘Periodic Law’ which states:
PERIODIC LAW - When arranged by increasing atomic number, the chemical elements display a regular and repeating pattern of chemical and physical properties.
(Everything in 1A had the SAME properties)

5. Periodic Law: (repeating pattern) Same number of valence electrons
= same properties = same group/family
Atoms with similar properties appear in groups or families (vertical columns) on the periodic table.
They are similar because they all have the same number of valence (outer shell) electrons, which governs their chemical behavior.

6. Metals, Nonmetals, Metalloids

7. Metals
Metals are lustrous (shiny), malleable, ductile, and are good conductors of heat and electricity.
They are mostly solids at room temp.
What is one exception?

8. Nonmetals Nonmetals are the opposite.
They are dull, brittle, nonconductors (insulators).
Some are solid, but many are gases, and Bromine is a liquid.

9. Metalloids Have some characteristics of metals, some of nonmetals.
For instance, silicon looks shiny, but is brittle and fairly poor conductor.

10. Metalloids Metalloids, aka semi-metals are just that.
They have characteristics of both metals and nonmetals.
They are shiny but brittle.
And they are semiconductors.
What is our most important semiconductor?

11. Which element is more NON-Metallic?

12. Which element is the MOST metallic?
Francium

13. Periodic Trends
There are several important atomic characteristics that show predictable trends that you should know.
The first and most important is atomic radius.
Radius is the distance from the center of the nucleus to the “edge” of the electron cloud.

14. Covalent Radius Nucleus
Two Br atoms bonded together are 2.86 angstroms apart. So, the radius of each atom is 1.43 Å.
2.86 Å
1.43 Å
Nucleus
Electron Cloud

15. Li – 2, 1
Period 2 = E2
Period 3 = E3
Na – 2,8, 1
Atomic radius increase down a group
K – 2,8,8, 1
Period 4 = E4
What do you think will happen to the radius across a period?
Rb – 2,8,18,8, 1
Period 5 = E5

16. Smallest Radius Largest Radius
Atomic Radius
 Increases
Smallest Radius
 Increases
Largest Radius

17. Effective Nuclear Charge (Z)
Atomic Radius
4P+
5P+
6P+
7P+
8P+
9P+ - + - + - + - +
Effective Nuclear Charge (Z)
Same Energy Level (2) – More positive protons  greater pull on electrons  smaller radius
Effective nuclear charge is the pull that an electron (negative) “feels” from the nucleus (positive).

18. Effective Nuclear Charge (Z)
Atomic Radius
Moving across a period, each element gains one proton
A more positive nucleus (more protons) has a greater pull on the electron cloud.
The nucleus is more positive and the electron cloud is more negative.
The increased attraction pulls the cloud in closer, making atoms smaller as we move from left to right across a period. - + - + - + - +
Effective Nuclear Charge (Z)

19. Smallest Radius Largest Radius
Atomic Radius
 Fewer Protons = Less Pull
Smallest Radius
 More Energy Levels
Largest Radius

20. Trends for Atomic Radius
NOTES = (Draw the box below)
Trends for Atomic Radius
Smallest Radius
Largest Radius

21. Which Element has the larger atomic radii?

22. Ionization Energy This is the second important periodic trend.
If an electron is given enough energy (in the form of a photon) to overcome the effective nuclear charge holding the electron in the cloud, it can leave the atom completely.
The atom has been “ionized” or charged.
The number of protons and electrons is no longer equal.

23. Ionization Energy
Ionization energy - The energy required to remove an electron from an atom . (measured in kilojoules, kJ)
-- Larger atom = Lower ionization energy
The larger the atom is, the further away the valence electrons are, the easier its electrons are to remove.
Ionization energy and atomic radius are inversely proportional.
Ionization energy is always endothermic, that is energy is added to the atom to remove the electron.

24. What is the trend?
Ionization Energy

25. Larger atom = Lower Ionization Energy
Effective nuclear charge is the pull that an electron (negative) “feels” from the nucleus (positive)
In the same energy level (period), FEWER protons  Weaker pull  Valence Electrons further from the nucleus  Larger Atom  Lower Ionization Energy need to remove an electron.. -

26. 3. Trend in Ionization Potential

27. Trends for Ionization energy
NOTES = (Draw the box below)
Trends for Ionization energy
Highest
Lowest

28. Which Element has the greater Ionization Energy?

29. Electron Affinity What does the word ‘affinity’ mean?
Electron affinity is the energy change that occurs when an atom gains an electron (also measured in kJ).
Where ionization energy is always endothermic (energy IN), electron affinity is usually exothermic (energy OUT), but not always.

30. Trends in Electron Affinity
Electron Affinity - The energy release when an electron is added to an atom.
--An affinity (attraction) of ADDITIONAL electrons
(same period) More protons  More Effective Nuclear Charge  Great pull on electrons  Greater affinity (attraction) of additional electrons.
4P+
5P+
6P+
7P+
8P+
9P+

31. Trends for Electron Affinity
NOTES = (Draw the box below)
Trends for Electron Affinity
Highest
Lowest

32. Highest Lowest Electronegativity
Electronegativity - a measure of an atom’s attraction for another atom’s shared electrons. (covalently bonded electrons)
Highest
Lowest

33. Which Element has the greater Electronegativity?

34. Overall Reactivity
This ties all the previous trends together in one package.
However, we must treat metals and nonmetals separately.
The most reactive metals are the largest since they are the best electron givers.
The most reactive nonmetals are the smallest ones, the best electron takers.

35. Overall Reactivity