Unit 2 – Electrons and Periodic Behavior

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

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

3. 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

4. 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

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

6. Propertiesof 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

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

8. 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

9. 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

10. The Properties of a Group: the Alkali Metals • 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)

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

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

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

14. The Bohr Model of the Atom 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!!! Neils Bohr

15. 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: 2n2

16. 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… Orbital shapes are defined as the surface that contains 90% of the total electron probability.

17. Energy Levels, Sublevels, Electrons

18. Orbital filling table

19. 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

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

21. Determination of Atomic Radius: 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

22. Table of Atomic Radii

23. ION • 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 negative charge when they gain electrons • Ionization is the process that results in the formation of an ion.

24. Ionization Energy - the energy required to remove an electron from an atom • 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

25. Table of 1st Ionization Energies

26. 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

27. Periodic Table of Electronegativities

28. Summation of Periodic Trends

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