Instructor: Dr. Robert Powers Office Address: 722 HaH Phone: 472-3039 e-mail:rpowers3@unl

1. NEVER FORGET Instructor: Dr. Robert Powers Office Address: 722 HaH Phone: 472-3039 e-mail:rpowers3@unl.edu web page: http://bionmr-c1.unl.edu September 11, 2001

2. Periodic Table Chemical Trends Periodicity in chemical properties is the basis of the periodic table arrangement • Periodicity of electron configuration: • Affects attraction of atom for its valence electrons • Affects attraction of valence electrons for additional electrons Determines chemical and physical properties of the elements

3. Periodic Table Chemical Trends 1s1 Hydrogen (gas) [Ar]3d104s1 Copper (solid) [Xe]5d106s2 Mercury (liquid)

4. Periodic Table • Chemical Trends • 1.)Chemical trends based on the combination of the electron configuration, octet rule and electronegativity • 2.)Electronegativity • a.) tendency to attract electrons in a compound • b.) empirically based range from 0.7 to 3.98 Attracts electrons Donate electrons

5. Periodic Table • Chemical Trends • 1.)Chemical trends based on the combination of the electron configuration, octet rule and electronegativity • 2.)Electronegativity High electronegativity pulls electrons away from elements with weaker electronegativity Low electronegativity easily loses electrons to elements with higher electronegativity

6. Periodic Table • Chemical Trends • 1.)Chemical trends based on the combination of the electron configuration, octet rule and electronegativity • 3.)The Octet Rule The representative elements achieve a noble-gas configuration (eight valence electrons) in most of their compounds, except hydrogen, which only has two valence electrons in its corresponding noble gas structure.

7. Periodic Table • Chemical Trends • 4.)Chemical reactions between Group IA elements and Group VIIA elements • Group IA – single valence electron easily removed  noble configuration • Group VIIA – easily attracts one electron  noble configuration (ns2p6) • Form 1:1 ionic compound where Group IA loses e- and Group VIIA gains e- • Ionic compounds are usually solids high ns1 ns2p5 low

8. Periodic Table • Chemical Trends • 5.)Electronegativity differences determine the outcome of a chemical reaction • Electronegativity of Chlorine is 3.16 • Electronegativity of Bromine is 2.96 Halogen ions have an octet in valence shell No need to share e- pale yellow clear dark brown clear • 2Br- has sixteen valence electrons (eight each) • Br2 has only fourteen valence electrons • Two electrons lost from two Br- • Two electrons gained by Cl2 to form 2Cl- The greater electronegativity of chlorine captures an electron from bromide

9. Periodic Table • Chemical Trends • 6.)Example: electronegativity difference determines chemical products Halides are expected to react similarly with water, but there are some important differences. Why? Answer: electronegativities: chlorine 3.16, oxygen 3.4, fluorine 3.98 fluorine can attract e- from oxygen - HF : eight valence electrons - O2 : six valence electrons chlorine can not attract e- from oxygen, instead attracts e- from hydrogen in water and replaces hydrogen in water - HCl : eight valence electrons - HOCl : Cl replaces H in water

10. Clicker Question

11. Clicker Question: What is a main factor that results in an atom having an increasing atomic radius compared to its neighbor? a) total number of electrons b) total number of protons and neutrons c) total number of electrons in the outer electron shell d) total number of electron shells

12. Periodic Table • Chemical Trends • 7.)Size of Atom Atomic radius – radius of the sphere containing 90% of the electron density for the free atom  related to electronic configuration Progressing from period to period • the valence shell is increasing far from the nucleus • increased separation of negatively charged electrons from positive charged protons • Size of the atoms and ions increase Increasing Atomic Radius

13. Periodic Table • Chemical Trends • 7.)Size of Atom Progressing from group to group • the valence shell is a constant • increased attraction between the negatively charged electrons from positive charged protons  all e- are drawn to the nucleus • Size of the atoms and ions decrease despite adding electrons • Minimal size change occurs for transition elements - fill inner shell d-orbitals that shield outer shell s-orbitals Decreasing Atomic Radius

14. Periodic Table • Chemical Trends • 7.)Size of Atom Changes in Size Affects Chemical Behavior Increase in: ionization energy electron affinity electronegativity Increase in attraction between nucleus and electrons Decrease in Radius

15. Periodic Table • Chemical Trends • 8.)Size of Ion When an atom gains or loses an electron, the ion is a different size than the neutral atom Like Charges Repel: Remove e- remove repulsion  smaller positive charged ion (cation) is smaller Add e-  add repulsion  larger negatively charged ion (anion) is larger Size difference can be dramatic, about a factor of 2

16. Periodic Table • Chemical Trends • 8.)Size of Ion When an atom gains or loses an electron, the ion is a different size than the neutral atom Like Charges Repel: Isoelectronic ions are bigger the greater the negative charge Again, greater nuclear charge can hold electrons closer than smaller nuclear charge 2s22p6: 7N3- > 8O2- > 9F- > 11Na+ > 12Mg2+ > 13Al3+ 171 140 133 102 72 50 picometers (pm)

17. Periodic Table • Chemical Trends • 9.)Example: converting mass density to molar and atomic density Given a density of 5.54 g/cm3 for titanium (Ti) and a density of 7.874 g/cm3 for iron (Fe), calculate the atomic density and atomic radius in the metals if Ti occupies 74% of the volume and Fe occupies 68% of the volume. • Solution: • Calculate Molar Density:

18. Periodic Table • Chemical Trends • 9.)Example: converting mass density to molar and atomic density Given a density of 5.54 g/cm3 for titanium (Ti) and a density of 7.874 g/cm3 for iron (Fe), calculate the atomic density and atomic radius in the metals if Ti occupies 74% of the volume and Fe occupies 68% of the volume. • Solution: • Calculate Atomic Density:

19. Periodic Table • Chemical Trends • 9.)Example: converting mass density to molar and atomic density Given a density of 5.54 g/cm3 for titanium (Ti) and a density of 7.874 g/cm3 for iron (Fe), calculate the atomic density and atomic radius in the metals if Ti occupies 74% of the volume and Fe occupies 68% of the volume. • Solution: • Calculate Volume per Atom in the Solid: • Calculate Atomic Volume:

20. Periodic Table • Chemical Trends • 9.)Example: converting mass density to molar and atomic density Given a density of 5.54 g/cm3 for titanium (Ti) and a density of 7.874 g/cm3 for iron (Fe), calculate the atomic density and atomic radius in the metals if Ti occupies 74% of the volume and Fe occupies 68% of the volume. • Solution: • Calculate Atomic Radius: Smaller than atomic radius because of interatomic interactions 200 pm 172 pm

21. Periodic Table • Trends in Physical Properties • 1.)Classification of the Elements • Elements in Periodic table are classified into three broad categories Nonmetals Semimetals Increasing metal characteristics Metals Metallic character associated with few valence s and p electrons and increases as those electrons are located farther from the nucleus

22. Periodic Table • Trends in Physical Properties • 1.)Classification of the Elements • Metals • Vast majority (~75%) of the elements • Left-hand of the periodic table • Defined by being: • Malleable – pounded into a sheet • Ductile – drawn into a wire • Most are solid at room temperature • Silvery shiny sheen • Conduct heat and electricity well • Low electronegativity values • Low ionization energy Valence electrons held loosely Facile movement of metal atoms over each other in solid

23. Periodic Table • Trends in Physical Properties • 1.)Classification of the Elements • Nonmetals • Right-side of the periodic table • Defined by being: • Variable physical states • Solids are brittle and poor conductors of heat and electricity • Insulating solids • high electronegativity values • Allotropes: different forms of the same elements with different properties • Carbon: - diamond: hardest material known  cutting tool - graphite: conductor, lubricant but not malleable or ductile - “bucky balls” Graphite Bucky ball Diamond

24. Periodic Table • Trends in Physical Properties • 1.)Classification of the Elements • Semimetals (metalloids) • Smallest number of elements • Fall between metals and nonmetals • Some properties common to metals others to nonmetals • Defined by being: • Solids at room temperature • Brittle • Poor conductors of electricity • Semiconductors: increasing conductivity with temperature properties • Metals conductivity decrease with temperature • Silicon (Si) and Germanium (Ge) Silicon wafer

25. gas solid Periodic Table • Trends in Physical Properties • 2.)Physical Form of the Elements • Phase of the elements at room temperature also reveals a periodic variation. • Most elements are solids, some are gases, few are liquids • Except for 1st period every period begins with solid and ends with gas • Different interactions among atoms of the element

26. Periodic Table • Trends in Physical Properties • 3.)Interactions and the Three Phases of Matter • Solids – holds its shape without support of a container • Interactions in solid must be strong • Liquids – adopt shape of container • Atoms in liquid flow readily over one another • Interactions are weaker than in a solid • Gas – expands to fill container • Interactions are very weak

27. Periodic Table • Trends in Physical Properties • 4.)Phase Transitions: transforming from a solid to a liquid and from a liquid to a gas Melting point Boiling point Gas Liquid Solid Freezing point Condensation point Increasing energy Decreasing energy Decreasing temperature Increasing temperature