2. “Welcome to the Periodic Kingdom… … This is a land of the imagination, but it is closer to reality than it appears to be. This is the Kingdom of chemical elements, the substances from which everything tangible is made. It is not an extensive country, for it consists of only a hundred or so regions…yet it accounts for everything material in our actual world” 1 1 Davis, R.E. et al, Modern Chemistry TE, Holt, Rinehart and Wiston company, NYC 2002, p.135.

3. Periodicity by Marta de Ortiz de Zevallos n To understand how the periodic table was created n and how it can be used n allows you to predict n “the properties of elements even if you never saw them”.

4. Before the development of the modern atomic theory, many elements were discovered. To be able to understand and predict their properties it was necessary to organize them. In 1869, Dimitri Mendeleev published his periodic table. In his table the elements were arranged in order of increasing atomic mass. The properties of the elements arranged in this way repeated periodically in vertical columns.

5. Mendeleev published another version of the periodic table in 1872 in which he left blank spaces for elements that were not known yet. He predicted their existence and the properties they should have. These elements were later discovered and the properties he predicted were very accurate for the time. His work “can be thought of as similar to putting together a large puzzle.” (Heath Chemistry)

6. How is the modern periodic table different from Mendeleev’s periodic table? The modern periodic table is similar to Mendeleev’s periodic table, but with a difference proposed by Henry Moseley to solve some discrepancies between some elements (Ar and K, I and Te). If they are put in order of increasing atomic mass their properties do not match with those of the elements in the same column. In the modern periodic table the elements are in order of increasing atomic number instead of mass.

7. PERIODIC LAW: “ The properties of the elements repeat periodically when they are arranged in increasing order by their atomic numbers.

8. The Periodic Table n Metals are at the left (red) n Non-metals at the right, except for H (blue) n Metalloids are between metals and non- metals and they have properties of both.

9. More about the PT… n Groups are also called families n Why? n Because the elements in a group share properties like the members of a family. It is divided into horizontal rows called periods and vertical columns called groups.

10. What is the charge? Group 1 (alkali metals): 1+ Group 17 (halogens): 1- 1+2+ 3+4-3-2-1- Group 2 (alkaline earth metals) : 2+ Group 13 (boron group): 3+ Group 16: 2- Group 15: 3- Group 14: 4- ? ??? The non metals in:

11. Now that you have learned the electron configuration of elements, what relationship do you see between the configuration, the position in the table and the charge the elements can get ? n n The elements in the same group have the same outer configuration. n They tend to acquire the same charge Why? n Because they all tend to become isoelec- tronic with the noble gases to complete their outermost s and p orbitals.

12. They have their outer level complete. They don’t “want” more electrons and they don’t “need” to give away electrons. … all the elements “want” to be like the noble gases so they tend to become isoelectronic with them Remember that the noble gases are the happy family!

13. How do properties vary in the PT? Metallic properties: 1) Increase from top to bottom and from right to left. Most active metals: Cs & Fr So the activity of the alkali metals increases from top to bottom. However the activity of the halogens (non metals of group 17) increases from bottom to top. The most active non metal is F

14. More physical properties Atomic radius (it gives a measure of the size of the atom) The atomic radii decrease from left to right and from bottom to top in the PT. http://ull.chemistry.uakron.edu/genobc/Chapter_03/

15. More physical properties The atomic radii increase from top to bottom. Why? Because as we move down a group the electrons are added to higher energy levels (electrons have the same outermost but with higher principal quantum number), so they are less attracted by the nucleus. Besides that, as there are more inner electrons, there is more shielding effect, wich also reduces the attraction of the outer electrons by the nucleus. The atomic radii decrease from left to right in the PT. Why? Because, as we move from left to right through a period of the PT, the nuclear charge increases attracting more the electrons that are added to the same energy level.

16. More physical properties First Ionization Energy Is the energy necessary to remove an electron from a neutral gaseous atom. Can be represented by the equation:  X(g)+ IE  X + + e- The smaller the IE, the greater the tendency of the element to form a positive ion. In the PT, especially for the representative elements, the IE increases from bottom to top and from left to right. http://ull.chemistry.uakron.edu/genobc/Chapter_03 /

17.   In general, the IE increases from left to right in the PT. However some exceptions are observed in each period. For example in period 2, when going from Be to B and from N to O, the IE decreases. In the case of Be to B the decrease is due to the filled 2s orbital which provides, in the case of B, some shielding to the electron in p. In the case of N to O the decrease is due to the extra repulsion in the doubly occupied p orbital. In the PT…

18. First Ionization Energy vs atomic number http://wulff.mit.edu/pt/pert9.html 1 st IE Atomic Number

19. More physical properties Ionic Size There are various factors that affect the size of an ion:.The nuclear charge.The repulsion of electrons.The level of energy of the outer electrons

20. Comparing the ion with the parent atom: Positive ions are smaller than the neutral atom Because they have the same nuclear charge attracting less electrons, therefore the attraction is stronger. For example K + < K Negative ions are larger than the neutral atom Because they have the same nuclear charge attracting more electrons, therefore the attraction is weaker. For example F - > F

21.   In a group, the ionic size increases from top to bottom The reason is the same as for the atomic radius. e- added to higher energy levels and more shielding effect.   In a period, it depends of the type of ions But negative ions decrease from left to right and positive ions also decrease from left to right. e- are added to the same level and Z increases In the PT…

22.  The size of isoelectronic ions (ions with the same number of electrons) decreases as the nuclear charge (Z) increases, because there are more protons to attract the same amount of electrons distributed in the same levels and with the same shielding effect. Example: O 2- > F - > Na + > Mg 2+

23. More physical properties Electron Affinity Is the energy change associated with the addition of an electron to a gaseous atom.  X(g)+ + e-  X - (g). It can be energy released or absorbed. When it is negative it’s energy released. The greater the tendency of the element to form negative ions the more negative the electron affinity.. Electron affinities usually become more negative from left to right in a period of the PT.. In going down a group the electron affinities become more positive because the electrons added are farther from the nucleus.The change is small though and there are several exceptions.

24. Electronegativity… Electronegativity is the ability of an atom in a molecule to attract shared electrons to itself.. The electronegativity increases from bottom to top and from left to right.. Fluorine is the most electronegative element.. Cesium and Francium are the least electronegative elements. http://ull.chemistry.uakron.edu/genobc/Chapter_03/

25. However we can observe some patterns in the melting points when moving through a period of the PT. The melting point increases until group 14 which includes solids such as C and Si which form giant molecules with covalent bonds between the atoms. Then the melting points decrease drastically as we get to groups 15, 16, 17 and especially the noble gases in group 18. (We will talk more about this when we study interparticle forces) Other properties like melting and boiling points and densities, depend on the attraction between particles.