1. Periodic Properties of Elements SANTOSH CHEMISTRY DEPT

2. The Periodic Table of Elements Elements are organized according to their physical and chemical properties in the Periodic Table of the Elements. Historically, several people contributed to this effort in the late 19th century: –Dobereiner- “triads”: Ca, Sr, Ba; Li, Na, K –Newlands- similarity between every eighth element –Mendeleev (1870) - Arranged elements according to atomic mass. Similar elements were arranged together in a “group”.

3. Triads of Elements

4. Mendeleev Father of the Periodic Table Periodic Law- Both physical and chemical properties of the elements vary periodically with increasing atomic mass. Exception placed Te (M = 127.6) a head of I (M=126.9) because Te was similar to Se and S, and I was similar to Cl and Br. Left gaps in periodic table and predicted new elements would be found. Predicted the new elements’ properties.

5. Example for “Eka-Silicon” Mendeleev’s predictionsObserved properties Property for “eka-silicon” of germanium (made in 1871)(discovered in 1886) Atomic mass7272.5 Density (g/mL)5.5 5.35 Specific Heat0.305 J/g-K 0.300 J/g-K Melting point ( o C)High947 ColorDark grayGrayish white Oxide formulaXO 2 GeO 2 Density of oxide4.7 g/mL4.70 g/mL Formula of chlorideXCl 4 GeCl 4

6. Periodicity (continued) –Meyer (1870)-Arranged elements according to their physical properties. –Elements changed properties gradually in a row or period. –Moseley (1930)- Arrange atoms according to atomic number (nuclear charge). He found a direct correlation between the square root of X- ray energy and nuclear charge (atomic number). Nuclear charge increases by one unit for each element.

7. Periods of Elements Periods of elements are the horizontal rows of the Periodic Table. The properties of the elements vary as you move from left to right across the periods. On the left, the periodic table starts with shiny reactive metals, followed by dull solids and reactive non-metals. Each period ends with a non-reactive noble gas

8. Valence Electrons Starting with one valence electron for the first element in a period, the number of electrons increases as you move from left to right across a period. The periodic changes in properties of elements coincide with their placement in the periodic table.

9. Groups and Families Vertical columns of elements in the periodic table are called groups or families. Elements in the same group or family have similar chemical properties. Representative Elements are those in the first two groups and the last six groups (s-block and p-block) in the periodic table. These groups are designated 1,2,13-18 or the A group elements

10. Electron Configurations can be Determined From the Position in the Periodic Table: Elements in group 1(1A) end in ns 1. Elements in group 2 (2A): end in ns 2 Elements in group 13 (3A) end in ns 2 np 1 Elements in group 14 (4A): end in ns 2 np 2 Elements in group 15 (5A) end in ns 2 np 3 Elements in group 16 (6A) end in ns 2 np 4 Elements in group 17 (7A) end in ns 2 np 5 Elements in group 18 (8A) end in ns 2 np 6

11. Periodic Trends in Properties of Elements Various Elemental Properties change fairly smoothly going across a period or down a group. Properties include: –Atomic and Ionic Radius –Ionization Energy –Melting Points and Boiling Points –Density and Conductivity

12. Atomic Size of Elements –Atomic size (radius) is based on the average distance between the outer electrons and the nucleus. –A measure of atomic size is the Atomic Radius (AR). –AR decreases as you move from left to right across a period. –AR increases as you move down a group

13. Trends in Atomic Radius

14. Relative Radii of Atoms

15. Periodic Trends in Atomic Radius

16. Ionic Radius When anions are formed, electron(s) are added, the radius increases. When cations are formed, electron(s) are lost, the radius decreases. Ionic radius decreases going down a group. Going from left to right across a period ionic radius decreases for cations, then increases for anions, then decreases.

17. Ionic Radius of Isoelectronic Atoms and Ions When chlorine forms an anion by adding an electron, it has the same electron configuration as argon the noble gas, [Ar]. The radius of a chloride ion is larger than the chlorine atom. It is also larger than the argon atom. When potassium forms a cation by losing an electron, it also has the same electron configuration as argon, yet the radius of the potassium cation is smaller than the potassium atom. It is also smaller than the argon atom. For isoelectronic ions, the radius decreases as the nuclear charge increases.

18. Comparing the Size of Atoms and Ions

19. An Isoelectronic Series C 4- N 3- O 2- F - Ne Na + Mg 2+ Al 3+ Increasing radius

20. Ionization Energy Ionization Energy (or Ionization Potential) –Ionization Energy (IE) is the energy required to remove one mole of electrons from one mole of gaseous atoms or ions. Na + IE Na + + e - IE increases (irregularly) as you move from left to right across a period. IE decreases (irregularly) as you move down a group.

21. Trend in Ionization Energy