GSCI 163

1. GSCI 163 Lecture 5

2. Review • Electrons in an atom are distributed in shells, orbitals and energy levels. • When electrons absorb photons they jump to higher orbitals • They move back up by emitting a photon whose energy correspond to the change in energy level

3. Activity • Finding the emission lines of different compounds.

4. Chemistry • Electrons in an atom are distributed in shells, orbitals and energy levels. • The way electrons are shared will determine how elements combine with each other to form compounds. • The highest or last shell of an atom is the valence shell • The valence shell determines the chemistry and properties

5. The periodic table

6. Various groups • Metals and non-metals • Metals tend to lose electrons in chemical reactions • Non-metals tend to gain (or share) electrons in chemical reactions Semi-metals have both metallic and non-metallic properties • Most reactive metal  Cesium • Most reactive non-metal  Fluorine

7. Noble gases • The valence shell is full. Thus they almost never react. • Argon gas (Ar) is used as an inert gas in light bulbs to prevent the filament, made of tungsten (W), from reacting under intense heat

8. Other families • Alkali metals • Only one valence electron; very soft metals • React so easily with Oxygen (O) and moisture that they need to be stored under oil • Alkaline earth metals • Two valence electrons; harder than alkali metals • Not so reactive. • Halogens • Seven electrons in the valence shell • Very active non-metals • Fluorine – highly corrosive, • Chlorine – purifying agent, • Bromine – desinfectant • Semi-metals (semi-conductors) • 3,4 or 5 electrons in the valence shell • Makes them behave both as metals and insulators

9. Atomic size • Increase when: • Add a new shell (moving down a group) since electrons are farther away from the nucleus • Number of protons decrease (across a period) since electrons are more loosely bound by electrostatic force He ~ 0.064 nm Cs ~ 0.47 nm

10. Ionization energy • Energy required to remove one electron from the outer shell Hardest elements to remove one electron from He H

11. Octet rule • Most common elements have electrons on the s and porbitals of their outmost shells • We can fit 2 electrons on s and 6 on p, with a total of 8 electrons Octet rule: atoms will combine with other atoms in such a way that gives a full shell of 8 electrons

12. Naming compounds • We represent compounds with a chemical formula: H2O • Names are also used to identify the compound unambiguously Symbol of the element Number of atoms of the element

13. Compounds with special names There are no rules for these. Their names are learned individually

14. Metal and a non-metal • Groups 1A, 2A plus Aluminum (Al), Zinc (Zn) and Silver (Ag). They form only one ion. • Rule for binary compounds: • Name of the metal + non-metal with ending –ide Examples: NaCl – Sodium Chloride Al2O3 – Ca3N2 –

15. Two non-metals • Rule: • The less metallic element (farther left and/or farther down the periodic table) comes first. The second is named with ending –ide . • For more than one element use Greek prefixes: di(2), tri(3), tetra(4), penta (5), hexa (6), hepta (7), octa (8). Examples: HCl – hydrogen chloride CS2 – PBr3 – IF7 –

16. Compounds with polyatomic ions • Metal plus a polyatomic ion: Rule: name of the metal + the name of of the polyatomic ion Example: ZnSO4 – Zinc Sulfate NaC2H3O2 – Mg(NO3)2 – K3PO4 –

17. Next class Calculating reactions • To prepare for the class read: • Handout pages 17 to 20 (day 5) • Presentation by Rebecca Cross, Acids and Bases • To prepare for the quiz read: • Handout pages 16 (day 4) • Power point for this class • Your class notes