Chapter Eight. The Periodic Table

Transcription

1 Chapter Eight The Periodic Table 1

2 Quantum Numbers and the Periodic Table Principle quantum number, n =1 to 7 Row number of periodic table Angular momentum quantum number, l= 0 to (n-1) Specific area of periodic table, spdf 2 Magnetic quantum number, m l = l to +l Number of orbitals = = 2l+1 Spin quantum number, m s=+1/2 or -1/2 Number of electrons, look at atomic number

3 Electronic Configurations and the Periodic Table Add 1 electron for each block in the periodic table 3

4 Mendeleev s Periodic Table 1869 Arranged the known elements in order of increasing atomic mass from left to right and from top to bottom in groups. 4 Elements with similar properties are placed in same column. O I II III IV V VI VII H 1 He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Ca Ge As Se Br Kr Rb Sr In Sn Sb Te I Xe Cs Ba Tl Pb Bi Rn (222) Used table to predict properties of undiscovered elements Eka-Silicon Germanium MM: 72 MM: 72.6 Density: 5.5g/mL Density: 5.47g/mL Color: dirty gray Color: grayish white

5 The Modern Periodic Table Representative Elements: (main group elements) Incomplete s or p shell determine elemental properties 5

6 Valence and Core Electrons Valence electrons: Highest shell farthest from nucleus Largest principal quantum number (n) Located on the outside of the atom Determine the behavior of the atom 6 Core electrons Located on the inside in inner shells. Principal quantum number is lower Example Oxygen, O Z = 8 valence electrons e- = 6 Core electrons e- = s 2s 2 p 2 4 2s 2 p 2 1s

7 Effect of Valence electrons on Elements Elements most stable with noble gas configuration Last column in periodic table No electrons want to be added or removed Octet rule satisfied (8 electrons= 2s + 6p) Isoelectronic: ion has same spdf as noble gas Helium (and Hydrogen) follow duet rule (2 electrons) 7 Main group elements Valence electrons: s 2 p 6 Electrons are added: form anions Electrons removed: form cations Transition metals All form cations Remove electrons from shell 4s before 3d, 5s before 4d, etc.

8 8 Periodic Properties in Main Group Elements

9 Atomic Radius Atomic radius increases from top to bottom in a group Electrons are shielded from nucleus Previous shells blocks attraction Effective nuclear charge decreases Large size difference between shells 9 Atomic radius decreases from left to right across a row Little shielding as all electrons in same shell Effective nuclear charge higher as protons added to nucleus Electrons draw closer to nucleus

10 Anions larger than atoms Low effective nuclear charge More electrons More repulsion Ionic Radius Cations smaller than atoms High effective nuclear charge Fewer electrons Less repulsion 10

11 Ionization Energy Energy needed to remove an e- from a gaseous atom (or ion) X(g) X + + (g) + 1e- Endothermic Decreases top to bottom: Electrons shielded from nucleus Increases from left to right: Atoms want to now gain electrons 11 3 rd ionization energy > 2 nd >1 st: Higher effective nuclear charge

12 Elemental Ionization Energies 12

13 Electron Affinity Energy released when an electron is added to a gaseous atom X(g) + 1e- X - (g) Exothermic 13 Increases bottom to top Small atom (F) High nuclear:e- attraction Increases left to right Small atom (F) High nuclear:e- attraction 2 nd electron affinities lower: Electrons add to already negative ion

14 14 Physical and Chemical Properties in Main Group Elements

15 Valence Properties of Hydrogen 15 Valence Characteristics: 1s 1 Single electron in valence shell Wants to lose electron to form H + (H 3 O + in water) Can gain a second electron to form hydrides, NaH, CaH 2. Diatomic: exists as H 2 (g) Location in Periodic Table Normally placed with group 1 elements Reactions: Hydride reactions: 2NaH(s) + 2H 2 O (l) 2NaOH(aq) + H 2 (g) Combustion: 2H 2 (g) + O 2 (g) 2H 2 O (l) Acid-Base: NaOH(aq) + HCl (aq) NaCl(aq) + H 2 O (l)

16 Valence Properties of Alkali Metals Valence Characteristics: ns 1, n 2 Single electron in valence shell is lost Forms +1 cation Low ionization energy Extremely reactive 16 Location in Table 1 st column, Group 1A Li, Na, K, Rb, Cs Reactions: With water: 2Na(s) + 2H 2 O (l) 2NaOH(aq) + H 2 (g) + heat Oxide formation: 4Li(s) + O 2 (g) 2Li 2 O (s) Other oxides can form: peroxide: Na 2 O 2, superoxide: KO 2

17 Valence Properties of Alkali Earth Metals Valence Characteristics: ns 2, n 2 Lose both s electrons Forms +2 cation 2 ionization energies Less reactive than 1A 17 Location in Table 2 nd column, Group 2A Be, Mg, Ca, Sr, Ba, Ra Reactions: With oxygen: 2Be(s) + O 2 (g) 2BeO (s) With water/steam: Ba(s) + 2H 2 O(l) Ba(OH) 2 (s) + H 2 (g) With acid: Mg(s) + H + (aq) Mg 2+ (aq) + H 2 (g) Reactivity increases going down, Be only reacts with O 2

18 Valence Properties of Group 3A Elements Valence Characteristics: ns 2 np 1, n 2 Lose s electrons & p electron Form +3 or +1 cations Weak metal characteristics Form molecular compounds Location in Table 3 rd column, Group 3A B, Al, Ga, I 18 Reactions: With oxygen: Al(s) + 3O 2 (g) 2Al 2 O 3 (s) With acid: 2Al(s) + H + (aq) Al 3+ (aq) + 3H 2 (g) Hydride formation: 2Al(s) + 3H 2 (g) 2AlH 3 (s) B is a metalloid and does not fully ionize Forms molecular compounds only

19 Valence Properties of Group 4A Elements Valence Characteristics: ns 2 np 2, n 2 Lose s electrons & p electrons +2 & +4 oxidation states Primarily molecular compounds Location in Table 4 th column, Group 4A C, Si, Ge, Sn, Pb 19 Reactions: With oxygen: C(s) + O 2 (g) CO 2 (g) also CO With acid: Pb(s) + 2H + (aq) Pb 2+ (aq) + H 2 (g) C is a nonmetal, Si and Ge are metalloids Pb and Sn are metals and can ionize C, Si and Ge form molecular compounds only

20 Valence Properties of Group 5A Elements Valence Characteristics: ns 2 np 3, n 2 May gain or lose electrons Variable oxidation states Can act as anions -3 charge in salt Location in Table 5 th column, Group 5A N, P are nonmetals As, Sb, Bi more metallic 20 Reactions: With oxygen: N(s) + O 2 (g) NO 2 (g) also NO, N 2 O, N 2 O 4 Acidic Oxides in water: N 2 O 5 (s) + H 2 O(l) 2HNO 3 (aq) P 4 O 10 (s) + H 2 O(l) 4H 3 PO 4 (aq)

21 Valence Properties of Group 6A Elements 21 Valence Characteristics: ns 2 np 4, n 2 Tend to gain electrons -2 most common charge Many molecular compounds Location in Table 6 th column, Group 6A O, S, Se, Te, Po Reactions: With water: SO 3 (g) + H 2 O(g) H 2 SO 4 (aq) Will form many nonmetal molecular compounds

22 Valence Properties of the Halogens Valence Characteristics: ns 2 np 5, n 2 Gain 1 electron -1 charge as an anion Positive oxidation state if bonded to each other, BrF 3 22 Location in Table 7 th column, Group 7A F, Cl, Br, I, At Reactions: Ref only With water: 2F 2 (g) + 2H 2 O(g) 4HF (aq) + O 2 (g) With hydrogen: H 2 (g) + X 2 (g) 4HX (g) (F 2 most reactive) All nonmetals, often designated with an X Larger halogens can have positive oxidation states All halogens are diatomic

23 Valence Properties of the Noble Gases Valence Characteristics: ns 2 np 6, n 2 Full octet: No desire to gain or lose electrons + charge if larger gases are forced to bond, XeF 4 Location in Table 8 th column, Group 8A: He, Ne, Ar, Kr, Xe 23 Reactions: Ref only Xe can react with oxygen and fluorine, but not easily All gases due to no desire to associate with other atoms