2. Unit 2 – Electrons and Periodic Behavior Cartoon courtesy of NearingZero.net

3. Mendeleev’s Periodic Table By the mid-1800s, about 70 elements were known to exist Dmitri Mendeleev – a Russian chemist and teacher Arranged elements in order of increasing atomic mass Thus, the first “Periodic Table”

4. A better arrangement In 1913, Henry Moseley – British physicist, arranged elements according to increasing atomic number The arrangement used today

5. The Periodic Table Period Group or family Period Group or Family

6. Periodic Table Periodic table is divided into 3 classes Metals Non metals Metalloids The horizontal rows are called periods while the vertical columns of the periodic table are called Groups or Families

7. Properties of Metals  Metals are good conductors of heat and electricity  Metals are malleable  Metals are ductile  Metals have high tensile strength  Metals have luster

8. Examples of Metals Potassium, K reacts with water and must be stored in kerosene Zinc, Zn, is more stable than potassium Copper, Cu, is a relatively soft metal, and a very good electrical conductor. Mercury, Hg, is the only metal that exists as a liquid at room temperature

9. Properties of Nonmetals Carbon, the graphite in “pencil lead” is a great example of a nonmetallic element.  Nonmetals are poor conductors of heat and electricity  Nonmetals tend to be brittle  Many nonmetals are gases at room temperature

10. Examples of Nonmetals Sulfur, S, was once known as “brimstone” Microspheres of phosphorus, P, a reactive nonmetal Graphite is not the only pure form of carbon, C. Diamond is also carbon; the color comes from impurities caught within the crystal structure

11. Properties of Metalloids Metalloids straddle the border between metals and nonmetals on the periodic table.  They have properties of both metals and nonmetals.  Metalloids are more brittle than metals, less brittle than most nonmetallic solids  Metalloids are semiconductors of electricity  Some metalloids possess metallic luster

12. Silicon, Si – A Metalloid  Silicon has metallic luster  Silicon is brittle like a nonmetal  Silicon is a semiconductor of electricity Other metalloids include:  Boron, B  Germanium, Ge  Arsenic, As  Antimony, Sb  Tellurium, Te

13. Easily lose valence electron (Reducing agents) React violently with water Large hydration energy React with halogens to form salts (valence electrons are electrons in the outermost shell of an atom) The Properties of a Group: the Alkali Metals

14. Properties of Alkaline earth metals They are the group II A elements They are the group II A elements Denser, harder and stronger than Group I A elements but less reactive Denser, harder and stronger than Group I A elements but less reactive Too reactive to be found pure in nature Too reactive to be found pure in nature

15. Halogens and Noble Gases Halogens are the most reactive of the non metals. Halogens are the most reactive of the non metals. They are the group VII A elements They are the group VII A elements The noble gases are the group VIII A elements. The noble gases are the group VIII A elements. They are also called inert gases because they undergo very few reactions. They are also called inert gases because they undergo very few reactions.

16. Periodic Law When elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties.

17. The Bohr Model of the Atom Neils Bohr I pictured electrons orbiting the nucleus much like planets orbiting the sun. But I was wrong! They’re more like bees around a hive. WRONG!!!

18. Electron Energy Level (Shell) Generally symbolized by n, it denotes the probable distance of the electron from the nucleus. Number of electrons that can fit in a shell: 2n 2

19. Orbital shapes are defined as the surface that contains 90% of the total electron probability. An orbital is a region within an energy level where there is a probability of finding an electron. This is a probability diagram for the s orbital in the first energy level…

20. Energy Level (n) Sublevels in main energy level (n sublevels) Number of orbitals per sublevel Number of Electrons per sublevel Number of electrons per main energy level (2n 2 ) 1s122 2spsp 1313 2626 8 3spdspd 135135 2 6 10 18 4spdfspdf 13571357 2 6 10 14 32 Energy Levels, Sublevels, Electrons

21. Orbital filling table

22. Irregular conformations of Cr and Cu Chromium steals a 4s electron to half fill its 3d sublevel Copper steals a 4s electron to FILL its 3d sublevel

23. Periodic Trends How do properties of elements change as you go across a periodic table?

24. Half of the distance between nuclei in covalently bonded diatomic molecule "covalent atomic radii" Periodic Trends in Atomic Radius Radius decreases across a period Increased effective nuclear charge due to decreased shielding Radius increases down a group Addition of principal quantum levels Determination of Atomic Radius:

25. Table of Atomic Radii

26. ION An atom or a group of atoms that has a positive or negative charge are called ions. An atom or a group of atoms that has a positive or negative charge are called ions. Atoms get a positive charge when they lose electrons Atoms get a positive charge when they lose electrons Atoms get a negative charge when they gain electrons Atoms get a negative charge when they gain electrons Ionization is the process that results in the formation of an ion. Ionization is the process that results in the formation of an ion.

27. Increases for successive electrons taken from the same atom Tends to increase across a period Electrons in the same quantum level do not shield as effectively as electrons in inner levels Irregularities at half filled and filled sublevels due to extra repulsion of electrons paired in orbitals, making them easier to remove Tends to decrease down a group Outer electrons are farther from the nucleus Ionization Energy - the energy required to remove an electron from an atom Ionization Energy - the energy required to remove an electron from an atom

28. Table of 1 st Ionization Energies

29. Electronegativity A measure of the ability of an atom in a chemical compound to attract electrons Electronegativities tend to increase across a period Electronegativities tend to decrease down a group or remain the same

30. Periodic Table of Electronegativities

31. Summation of Periodic Trends

32. Ionic Radii Cations Positively charged ions formed when an atom of a metal loses one or more electrons Smaller than the corresponding atom Anions  Negatively charged ions formed when nonmetallic atoms gain one or more electrons  Larger than the corresponding atom