Ch # 6

1. Ch # 6 Electronic Structure and Chemical Periodicity.

2. The Periodic Law: • It states that when elements are arranged in increasing atomic number, the elements with similar chemical behaviors occur periodically.

3. The Periodic table: • It is a tabular arrangement of elements in order of increasing atomic number. Elements having the same chemical behaviors are grouped together in a vertical column called a group.

4. The Periodic table: • Each element is represented in a square box, which contains: • Symbol, atomic number, atomic mass number of an element.

7. Periods and Groups of Elements: • Period: A horizontal row of elements. • There are 7 periods. • The first period contains only two elements H and He. • Groups: A vertical column in the periodic table. • All elements in same groups have similar chemical properties.

8. Periods and Groups of Elements: • There are 18 groups. • Group 1A= alkali metals. Except H. React violently with water. • Group II A= alkaline Earth metals. Do not react in water. • Group VII A=Halogens. Very reactive colored gases. • Group VIII A= Noble or inert gases. Very unreactive

9. Periods and Groups of Elements: • B groups= Transition elements. • Extension of period 6=Lanthanides. • Extension of period 7= Actinides. • The metals lie to the left of the table. Nonmetals to the right. They are separated by a step up ladder. • In between this ladder are the metalloids.

10. The Shape of the Periodic Table: • Lanthanides, Actinides.

11. The Energy of an electron: • 1. subatomic particle. • 2. They have very little mass compared to proton and Neutrons. 3. Located outside the nucleus. • 4. Move around the nucleus in a volume that defines the Size of the atom.

12. The Energy of an electron: • In 1926 Schrodinger showed that laws of quantum mechanics could be used to characterize the motion of electrons. • A quantized property is a property that can have only certain values. • The energy of an electron is quantized, only certain behavior patterns are allowed.

13. Electron Shells • Electrons with higher energy have higher velocity and thus they move farther away from the nucleus.

14. Electron shell • A region in space about a nucleus that contains electrons that have approximately the same energy and that spend most of their time approximately the same distance from the nucleus.

15. Electron shell • “n” is used to identify each electron shell. • Electron energy increases as its distance from nucleus increases. • Shell energy capacity = 2n2, where n is shell number. • 7 shells maximum. • Shell # 1 has 2e, 2 has 8 es, 3 has 18 es, 4 has 32 es.

16. Electron Subshells: • A region of space within an electron shell that contains electrons that have the same energy. • Number of subshells in a shell=n, n= shell number. • The letters s, p, d, f in order indicate energies of the subshells. • S=2 es, p=6 es, d=10 es, f=14 es. • Total number of electrons in shell 1=_______, shell 2=____ shell 3=___ shell 4=___-.

19. Electron orbitals: • A region of space within an electron subshell where an electron with a specific energy is most likely to be found. • S subshell=1 orbital, p subshell=3 orbitals, d subshell=5 orbitals, f subshell=7 orbitals. • Maximum number of electrons in a subshell is always 2. • S orbital=spherical, p orbital =dumbbell shaped.

23. Electron Spin • : Property of an electron associated with its spinning on its own axis. • Pauli's exclusion Principle: The maximum number of electrons in any orbital is two and they are spinning in the opposite directions.

24. Electron Configurations • A statement of how many electrons an atom has in each of its subshells.

25. Aufbau Principle • : It states that electrons normally occupy electron subshells in an atom in order of increasing subshell energy. • Subshells are filled in order of increasing energy.

26. Aufbau Diagram: • Listing of electron subshells in the order in which electrons occupy them.

27. Orbital Diagrams • Two principles to be considered are The Aufbau’s principle and Hund’s rule. • A diagram that shows how many electrons an atom has in each of its occupied electron orbitals.

28. Hund’s Rule • It states that when electrons are placed in a set of orbitals of equal energy the order of filling the orbitals is such that each orbital will be occupied by one electron before any orbital receives a second electron. This minimizes the repulsion between the electrons.

29. Orbital Diagrams • Paired electrons: Two electrons of opposite spin present in the same orbital. • Unpaired electron: A single electron in an orbital.

30. Orbital diagram • Paramagnetic atom: An atom that has an electron arrangement containing one or more unpaired electrons. • Diamagnetic atom: It is an atom that has an electron arrangement in which all electrons are paired.

31. Electronic configurations and The periodic Law • Chemical properties repeat themselves in a repeated manner because electronic configurations repeat themselves. • Group number indicates the number of valence electrons in atom. • Valence electrons are the electrons that can loose, gain or be shared in chemical reactions. • Group 1=1 valence electron, group 7= 7 valence electrons.

32. Electronic Configurations and The Periodic Table • S area has 2 columns. • P area has 6 columns. • D area has 10 columns. • F area has 14 columns.

37. Electronic Configurations and The Periodic Table • Distinguishing Electron: Last electron added to the element’s electronic configuration when the configuration is written according to Aufbau principle. • All elements in the first column of a specific area contain 1 electron, second column contains 2 electrons ------.

38. Electronic Configurations and The Periodic Table • Shell number=period number. • For d area shell number=period number-1. • For f area shell number=period number-2.

39. Classification Systems for the Elements: • A noble gas element: group VIII A. All elements are gases. Do not react.All have 8 electrons around them , other than He. • A representative element: Located in s area or first 5 columns of the p area. • Transition element: Element located in d area • Inner transition element: Located in the f area of periodic table.

41. Based on physical properties: • Metals: luster, thermal conductivity, electrical conductivity, malleable, ductile. • All metals are solid , except Hg. • High density and high melting points. • Ex: Al, Fe. Cu, Zn, Ag, Au.(91 elements) • Left of periodic table, zigzag line

42. Based on physical properties: • Nonmetals: no luster, not malleable, not ductile, not good conductors. • Gases at RT, except: Br-liquid. • Lower densities, low Melting points. • Ex: C,S, P.(22 elements) • Right of periodic table, zigzag line. • Earth’s crust contains: O,Si,H.

44. Chemical Periodicity: • The variation in properties of elements as a function of their positions in the Periodic Table.

45. Metallic and Nonmetallic Character: • Metallic character increases right to left, in a period. • It increases from top to bottom in a group. • Nonmetallic character increases from left to right in a period. • Nonmetallic character increases from bottom to top in a group.

47. Metalloid: • Element that possess properties both of metals and nonmetals. Ex: Si, Ge Sb

48. Semiconductor: • An element that does not conduct electric current at room temperature but does so at higher temperature.

50. Atomic Size: • Unit for atomic radii is picometer. • Range is 50-200 pm. • Atomic radii decreases from left to right within a period. • Atomic radii increases from top to bottom within a group.