1. Bond Types Unit 6 Chapter 12

2. Type Cast When we look at various compounds, we see some very basic differences Different substances fall into three categories: Ionic Covalent Metallic

3. Ionic Substances Form when two or more ions combine. All ionic compounds are called salts. They have very high melting points (CaCl 2 = 772°C) All of them are solid at room temperature – the only exceptions are really complex organic molecules!

4. Ionic Substances Will dissociate in water (if they dissolve) Will not dissolve in Oil Conductivity As a solid, ionic compounds are insulators When molten (liquid) & aqueous, they are conductors Examples: NaBr, MgF 2, AlCl 3, CsOH

5. Covalent Substances Usually form between a nonmetal and another nonmetal. They have low melting points. They can be solids, liquids, or gases at room temperature. They may dissolve in water or oil – but usually not both

6. Covalent Substances Two different types of covalent compounds: Polar and Nonpolar They will not dissociate in water. Will not conduct electricity (though there are a few exceptions) Examples: H 2 O, N 2, CCl 4, CH 4, C 8 H 18, SF 6, CO 2, SiO 2, S 8

7. Metallic Substances Form from metals Can be pure metals or alloys Usually solid, but a few liquids at or near room temperature. They will not dissolve in Water or Oil

8. Metallic Substances May react with water (forming H 2 & a salt) All metals conduct electricity at least a little bit. Examples: Fe, Cu 3 Zn 2 (Brass), Na, Mg, Ag 29 Cu 4 (Sterling Silver)

9. It’s all about the Electrons Bonds form between atoms due to the interactions of electrons. Core Electrons Electrons closest to the nucleus Unable to participate in bonding Shielded by electrons farther away Valence Electrons Electrons farthest from the nucleus Determine the chemical reactivity of the atom

10. What’s the Difference? Ionic Bonds form when electrons are transferred from one atom to another. Bonding = Electrostatic attraction b/w positively and negatively charged ions – no physical connection! Covalent Bonds form when electrons are shared between two atoms. Bonding = Physical connection via overlap of shared electron’s wavefunction! Metallic Bonds form when electrons between atoms are delocalized and are free to move around in an electron sea. Bonding = Electrostatic attraction b/w positively charged metal atoms (not ions) and negatively charged electron sea!  electrical conductivity & malleability.

11. How Do We Know Bond Type? Metallic bonds form between metals There is no distinct line between covalent and ionic bonds Remember, Ionic bonds transfer electrons Covalent bonds share electrons Na Cl +1 Cl Na K K K K

12. The Tug of War Ionic or Covalent – it depends on who pulls stronger! Recall: Electronegativity is a measure of how much an atom wants another electron. Think of it as how strong an atom is in a tug of war!

13. The Tug of War Elements with high electronegativity will pull electrons away from those with low electronegativity. Atoms with similar electronegativity will share electrons. Few bonds are strictly ionic or covalent. Ionic Character is the difference in electronegativity b/w bonding atoms.

14. Defining Ionic Character If the difference is  0.4, bond is covalent The e - is equally shared. If the difference is  1.6 = Polar Covalent Unequal Sharing – e - pulled more to one side. If the difference is > 1.6 = Ionic e - is transferred from one atom to the other.

15. Exceptions…Of Course Some compounds behave ionically even though their ENeg difference is < 1.6 HCl ionizes completely in water (ionic) Some compounds behave covalently even though their ENeg difference is > 1.6 HF is a gaseous molecule.

16. Comparison of Bond Types Ca F I I O C F +2 O Ionic Bond Polar Covalent Bonds Covalent Bond