1. Formation of compounds

2. Salt: a familiar compound Sodium Chloride – NaCl (1 sodium with 1 chlorine) Uses flavor enhancer, manufacture sodium and chlorine, melt ice Physical properties: White, crystalline cube shape, brittle,800*C mp, solid non conductor, liquid conductor as well as aqueous Chemical properties: stable (unreactive)

3. Sodium and Chlorine Properties of sodium (Na)- shiny, silvery-white, soft, metal, 98*C mp, so reactive stored in oil, not found free Properties of Chlorine (Cl 2 )– Pale green, poisonous gas, odor, kills living cells, soluble in water, disinfectant, -34*C bp,

4. Carbon dioxide CO 2 formula (1 carbon and 2 oxygen) Colorless gas, metabolic by-product, used for photosynthesis Physical properties: odorless, tasteless, -80*C bp - sublimes into dry ice, soluble in water, weak conductor (aq), burn C to make Chemical properties: stable, some fire extinguishers – not support burning.

5. Carbon and oxygen Carbon – nonmetal, black, burns, organic chemistry studies. Oxygen – nonmetal, colorless, odorless, gas, 21% air, supports burning (reacts), -183*C bp, slightly soluble in water (fish gills), 46% of Earth’s crust

6. Water H 2 O formula (2 hydrogen and 1 water) Occurs in all 3 states of matter, 100*C bp, 0*C mp, Pure water – non conductor, universal solvent Stable, medium for chemical reactions, photosynthesis starting material,

7. Hydrogen and oxygen Hydrogen: Lightest, most abundant element in universe, nonmetal, odorless, colorless, gas, reactive –seldom free, -253 bp, nonconductor, slightly soluble Oxygen: same as before.

8. How elements form compounds Atoms of the element must collide to react their electron clouds. The outer, valence electrons are chiefly responsible for chemical properties and how they will react. Noble gas chemical stability – not a single compound found naturally, (Xe and Kr artificially made with F using high temperature and pressure)

9. Octet rule Each noble gas has a filled valence shell, He with 2 and the rest with 8. Octet rule state that atoms can become stable by having 8 electrons in the outer energy level. This is known as a noble gas configuration.

10. Electrons can be transferred Na (metal) with 1 valence electrons transfers its electron to Chlorine (nonmetal) with 7 valence electrons, to form ions (atoms with a charge due to loss or gain of electrons). Sodium ion is now like Neon and Chlorine is now like Argon. The ion opposite charges attract each other forming an ionic bond. The shape for NaCl is a crystal, a regular repeating arrangement of atoms, ions or molecules.

11. Ionic compounds properties Solid, hard, brittle, crystal, high melting and boiling points, electrolyte – conducts electricity when dissolved in water due to the formation of ions. All are macroscopic evidence for the strength and rigidity of the submicroscopic structure of the salt crystal.

12. Electrons can be shared Hydrogen (nonmetal) and oxygen (nonmetal) in water. They collide with enough energy to react, but not enough to take electron, they combine by sharing. Attraction of 2 atoms by sharing a pair of electrons is called a covalent bond. Compound held together this way is a covalent compound. A molecule is an uncharged group of 2+ atoms held together by a covalent bond.

13. Steps for writing electron- dot structures Step 1 Determine the total number of valence electrons in all atoms Step 2 Place singe bonds between set of atoms. Each single bond uses 2 valence electrons Step 3 Subtract the electrons used to bond the atoms, and arrange the remaining to give each atom an octet. Hydrogen only need a single bond. Step 4 If octet of all atoms cannot be completed using the remaining elects, rearrange to for a double or triple bond. Check for octet for each.

14. More than 2 electrons can be shared When charcoal burns, carbon atoms collide with oxygen to form CO 2. When you put together, oxygen still need 1 electron each. They share 2 pairs of electrons, forming a double covalent bond.

15. Explaining properties of covalent compounds The forces between particles that make up a substance are called interparticle forces. The difference in strength explains the properties. Many Covalent compound are liquid or gases at room temperature (sugar is crystal solid – low melting point), nonconductor in pure state.