CHAPTER 2: A tomic structure and interatomic bonding

1. CHAPTER 2:Atomic structure and interatomic bonding ISSUES TO ADDRESS... • What promotes bonding? • What types of bonds are there? • What properties are dependent on bonding?

2. Atomic Structure } 1.67 x 10-27 kg • atom – electrons – 9.11 x 10-31 kg protonsneutrons • 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 1023 molecules or atoms amu – atomic mass unit 1 amu/atom = 1g/mol C 12.011 H 1.008 etc.

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 • Chemical • Electrical • Thermal • Optical

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. 4d N-shell n = 4 4p 3d 4s 3p M-shell n = 3 Energy 3s 2p L-shell n = 2 2s 1s K-shell n = 1 Electron Energy States Electrons... • have discrete energy states (2,6,10,14) • tend to occupy lowest available energy state.

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. SURVEY OF ELEMENTS Element Atomic # Electron configuration Hydrogen 1 1s 1 Helium 2 (stable) 1s 2 Lithium 3 1s 2 2s 1 Beryllium 4 1s 2 2s 2 Boron 5 1s 2 2s 2 2p 1 1s 2 2s 2 2p 2 Carbon 6 ... ... Neon 10 1s 2 2s 2 2p 6 (stable) Sodium 11 1s 2 2s 2 2p 6 3s 1 1s 2 2s 2 2p 6 3s 2 Magnesium 12 1s 2 2s 2 2p 6 3s 2 3p 1 Aluminum 13 ... ... 1s 2 2s 2 2p 6 3s 2 3p 6 (stable) Argon 18 ... ... ... Krypton 36 1s 2 2s 2 2p 6 3s 2 3p 6 3d 10 4s 2 4p 6 (stable) • Most elements: Electron configuration not stable.

8. valence electrons 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) 1s22s2 2p2

9. 1s2 2s2 2p6 3s2 3p6 3d6 4s2 valence electrons 4d N-shell n = 4 4p 3d 4s 3p M-shell n = 3 Energy 3s 2p L-shell n = 2 2s 1s K-shell n = 1 Electronic Configurations 26 ex: Fe - atomic # =

10. inert gases give up 1e give up 2e accept 2e accept 1e give up 3e H He Li Be O F Ne Na Mg S Cl Ar K Ca Sc Se Br Kr Rb Sr Y Te I Xe Cs Ba Po At Rn Fr Ra The Periodic Table • Columns: Similar Valence Structure Atomic # Electropositive elements: Readily give up electrons to become (+ ions). Electronegative elements: Readily accept electrons to become (- ions).

11. 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

12. Electronegativity • Ranges from 0.7 to 4.0, • Large values: tendency to acquire electrons. Smaller electronegativity Larger electronegativity

13. 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

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. Ion cores + + + + + + + + + Sea of valence electrons

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, ironically and covalently bonded materials are typically electrical and thermal insulators, due to the absence of large numbers of free electrons.

17. Ionic bond – metal + nonmetal donates accepts electrons electrons Dissimilar electronegativities   ex: MgOMg 1s2 2s2 2p63s2O 1s2 2s2 2p4 [Ne] 3s2 Mg2+1s2 2s2 2p6O2- 1s2 2s2 2p6

18. Ionic Bonding Na (metal) Cl (nonmetal) unstable unstable electron - Na (cation) + Cl (anion) stable stable Coulombic Attraction • 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)

19. Examples: Ionic Bonding NaCl MgO CaF 2 CsCl Give up electrons Accept electrons • Predominant bonding in Ceramics

20. Covalent Bonding shared electrons H from carbon atom CH 4 H H C shared electrons from hydrogen H atoms • similar electronegativity share electrons • bonds determined by valence – s & p orbitals dominate bonding • Example: CH4 C: has 4 valence e-, needs 4 more H: has 1 valence e-, needs 1 more Electronegativities are comparable.

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

22. Summary: Primary Bonds secondary bonding Ceramics Large bond energy large Tm large E small a (Ionic & covalent bonding): Metals Variable bond energy moderate Tm moderate E moderate a (Metallic bonding): Polymers Directional Properties Secondary bonding dominates small Tm small E large a (Covalent & Secondary):