1. Chapter 2 - 1 ISSUES TO ADDRESS... What promotes bonding? What types of bonds are there? What properties are dependent on bonding? CHAPTER 2: A tomic structure and interatomic bonding

2. Chapter 2 - 2 Atomic Structure atom – electrons – 9.11 x 10 -31 kg protons neutrons atomic number = # of protons in nucleus of atom = # of electrons of neutral electrically or complete atom atomic mass = the sum of the masses of proton and neutrons within the nucleus Atomic wt = wt of 6.023 x 10 23 molecules or atoms amu – atomic mass unit 1 amu/atom = 1g/mol C 12.011 H 1.008 etc. } 1.67 x 10 -27 kg

3. Chapter 2 - 3 Atomic Structure Valence electrons are those that occupy the outermost shell. These electrons are extremely important, they participate in the bonding between atoms to form atomic and molecular aggregates. Valence electrons determine all of the following properties 1)Chemical 2)Electrical 3)Thermal 4)Optical

4. Chapter 2 - 4 Electronic Structure Electrons have wavelike and particulate properties. –This means that electrons are in orbitals defined by a probability. –Each orbital at discrete energy level determined by quantum numbers. Quantum # Designation n = principal (energy level-shell)K, L, M, N, O (1, 2, 3, etc.) l = subsidiary (orbitals)s, p, d, f (0, 1, 2, 3,…, n -1)

5. Chapter 2 - 5 Electron Energy States 1s1s 2s2s 2p2p K-shell n = 1 L-shell n = 2 3s3s 3p3p M-shell n = 3 3d3d 4s4s 4p4p 4d4d Energy N-shell n = 4 have discrete energy states (2,6,10,14) tend to occupy lowest available energy state. Electrons...

6. Chapter 2 - 6 The order by which the electrons fill up orbitals is as follows: The electron configuration of the elements is determined experimentally. It is noted that there are some irregularities inconsistent with the previously listed system. For ex, copper ( Z=29) has the outer electron configuration to be One would expect The reason for these irregularities is not precisely know

7. Chapter 2 - 7 Most elements: Electron configuration not stable. SURVEY OF ELEMENTS Electron configuration (stable)... 1s1s 2 2s2s 2 2p2p 6 3s3s 2 3p3p 6 (stable)... 1s1s 2 2s2s 2 2p2p 6 3s3s 2 3p3p 6 3d3d 10 4s4s 2 4p4p 6 (stable) Atomic # 18... 36 Element 1s1s 1 1Hydrogen 1s1s 2 2Helium 1s1s 2 2s2s 1 3Lithium 1s1s 2 2s2s 2 4Beryllium 1s1s 2 2s2s 2 2p2p 1 5Boron 1s1s 2 2s2s 2 2p2p 2 6Carbon... 1s1s 2 2s2s 2 2p2p 6 (stable) 10Neon 1s1s 2 2s2s 2 2p2p 6 3s3s 1 11Sodium 1s1s 2 2s2s 2 2p2p 6 3s3s 2 12Magnesium 1s1s 2 2s2s 2 2p2p 6 3s3s 2 3p3p 1 13Aluminum... Argon... Krypton

8. Chapter 2 - 8 Electron Configurations Valence electrons – those in unfilled shells Filled shells more stable Valence electrons are most available for bonding and tend to control the chemical properties –example: C (atomic number = 6) 1s 2 2s 2 2p 2 valence electrons

9. Chapter 2 - 9 Electronic Configurations ex: Fe - atomic # = 26 valence electrons 1s1s 2s2s 2p2p K-shell n = 1 L-shell n = 2 3s3s 3p3p M-shell n = 3 3d3d 4s4s 4p4p 4d4d Energy N-shell n = 4 1s 2 2s 2 2p 6 3s 2 3p 6 3d 6 4s 2

10. Chapter 2 - 10 The Periodic Table Columns: Similar Valence Structure Electropositive elements: Readily give up electrons to become (+ ions). Electronegative elements: Readily accept electrons to become (- ions). give up 1e give up 2e give up 3e inert gases accept 1eaccept 2e O Se Te PoAt I Br He Ne Ar Kr Xe Rn F ClS LiBe H NaMg BaCs RaFr CaKSc SrRbY Atomic #

11. Chapter 2 - The Periodic Table all elements have been classified according to electron configuration in the periodic table Here the elements are situated, with increasing atomic number, in seven horizontal rows called period The arrangement in such that all elements arrayed in a given column or group have similar valence electron structures, as well as chemical and physical properties 11

12. Chapter 2 - 12 Ranges from 0.7 to 4.0, Smaller electronegativityLarger electronegativity Large values: tendency to acquire electrons. Electronegativity

13. Chapter 2 - Atomic bonding in solid Primary ( or chemical) bonds : – metallic – ionic – covalent secondary ( or physical) forces: – van der walls bonding – Are weak in comparison to the primary o chemical ones –Secondary bonding is evidenced for the inert gases, which have stable electron structures, and, in addition, between molecules in molecular structures that are covalently bonded –Hydrogen bonding, a special type of secondary bonding, is found to exist between some molecules that have hydrogen as one of the constituents 13

14. Chapter 2 - 14 Metallic Bonding It is found in metals and their alloys Is nondirectional in character Bonding may be strong or weak; bonding energies range from 68 kJ/mol for mercury to 850 kJ/mol for tungsten. Their respective melting temperatures are -39 and 3410 C

15. Chapter 2 - 15 + + + + + + + + + Ion cores Sea of valence electrons

16. Chapter 2 - 16 Some general behavior of the various material types (i.e., metals, ceramics, and polymers) may be explained by bonding type. For example, metals are good conductors of both electricity and heat, as a consequence of their free electrons. By the way of contrast, ionically and covalently bonded materials are typically electrical and thermal insulators, due to the absence of large numbers of free electrons.

17. Chapter 2 - 17 Ionic bond – metal + nonmetal donates accepts electrons electrons Dissimilar electronegativities ex: MgOMg 1s 2 2s 2 2p 6 3s 2 O 1s 2 2s 2 2p 4 [Ne] 3s 2 Mg 2+ 1s 2 2s 2 2p 6 O 2- 1s 2 2s 2 2p 6

18. Chapter 2 - 18 Occurs between + and – ions.( metalic+nonmetalic) elem Requires electron transfer.( high electroneg+high electropoz) Large difference in electronegativity required. Example: NaCl ( Na=11, Cl=17) Ionic Bonding Na (metal) unstable Cl (nonmetal) unstable electron + - Coulombic Attraction Na (cation) stable Cl (anion) stable

19. Chapter 2 - 19 Predominant bonding in Ceramics Examples: Ionic Bonding Give up electronsAccept electrons NaCl MgO CaF 2 CsCl

20. Chapter 2 - C: has 4 valence e -, needs 4 more H: has 1 valence e -, needs 1 more Electronegativities are comparable. Covalent Bonding similar electronegativity  share electrons bonds determined by valence – s & p orbitals dominate bonding Example: CH 4 shared electrons from carbon atom shared electrons from hydrogen atoms H H H H C CH 4

21. Chapter 2 - 21 Primary Bonding Ionic-Covalent Mixed Bonding % ionic character = where X A & X B are Pauling electronegativities %)100( x Ex: MgOX Mg = 1.3 X O = 3.5

22. Chapter 2 - Arises from interaction between dipoles Permanent dipoles-molecule induced Fluctuating dipoles -general case: -ex: liquid HCl -ex: polymer SECONDARY BONDING asymmetric electron clouds +-+- secondary bonding HHHH H 2 H 2 secondary bonding ex: liquid H 2 H Cl H secondary bonding secondary bonding +-+- secondary bonding

23. Chapter 2 - 23 Type Ionic Covalent Metallic Secondary Bond Energy Large! Variable large-Diamond small-Bismuth Variable large-Tungsten small-Mercury smallest Comments Nondirectional (ceramics) Directional (semiconductors, ceramics polymer chains) Nondirectional (metals) Directional inter-chain (polymer) inter-molecular Summary: Bonding

24. Chapter 2 - 24 Bond length, r Bond energy, E o Melting Temperature, T m T m is larger if E o is larger. Properties From Bonding: T m r o r Energy r larger T m smaller T m EoEo = “bond energy” Energy r o r unstretched length

25. Chapter 2 - 25 Coefficient of thermal expansion,   ~ symmetry at r o  is smaller if E o is larger. Properties From Bonding :  =  (T 2 -T 1 )  L L o coeff. thermal expansion  L length,L o unheated, T 1 heated, T 2 r o r larger  smaller  Energy unstretched length EoEo EoEo

26. Chapter 2 - 26 Ceramics (Ionic & covalent bonding): Metals (Metallic bonding): Polymers (Covalent & Secondary): Large bond energy large T m large E small  Variable bond energy moderate T m moderate E moderate  Directional Properties Secondary bonding dominates small T m small E large  Summary: Primary Bonds secondary bonding