7-2: Covalent Bonding

Covalent Bonds in Water

Covalent Bond: Formed when two atoms SHARE a PAIR of electrons. Formed when two atoms SHARE a PAIR of electrons. Each atom donates an electron to make the SHARED PAIR. Each atom donates an electron to make the SHARED PAIR. Molecule: atoms joined by a covalent bond. Molecule: atoms joined by a covalent bond.

Examples of covalent compounds Water Water DNA DNA Gasoline Gasoline Glucose Glucose

Types of Formulas for Covalent Cmpds. Molecular formula: gives numbers and kinds of atoms present Molecular formula: gives numbers and kinds of atoms present Empirical formula: smallest whole number ratio of atoms Empirical formula: smallest whole number ratio of atoms Structural formula: shows which atoms are bonded to each other Structural formula: shows which atoms are bonded to each other

Covalent Bond Miscellanous Unshared pair: a pair of electrons that are not bonded Unshared pair: a pair of electrons that are not bonded One dash between two atoms represents a bond One dash between two atoms represents a bond Single bond: 2 electrons (1 PAIR) shared Single bond: 2 electrons (1 PAIR) shared Example: propane gas, water Example: propane gas, water Double bond: 4 electrons (2 PAIR) shared Double bond: 4 electrons (2 PAIR) shared Example: acetone Example: acetone Triple bond: 6 electrons (3 PAIR) shared Triple bond: 6 electrons (3 PAIR) shared Example: acetylene gas Example: acetylene gas

Properties of Covalent Bonds Some atoms do not share electrons equally. Some atoms do not share electrons equally. Why? Why? A more electronegative atom will pull more on the electrons that are being shared. A more electronegative atom will pull more on the electrons that are being shared. This creates an unbalance – a polar bond – a covalent bond in which one atom is significantly more electronegative that the other This creates an unbalance – a polar bond – a covalent bond in which one atom is significantly more electronegative that the other Water is an example Water is an example

Properties of Covalent Bonds Non-polar bond: a covalent bond in which atoms share electrons equally. Example: methane, hydrogen gas Non-polar bond: a covalent bond in which atoms share electrons equally. Example: methane, hydrogen gas

Electro- negativity Difference Bond Type Description ≤0.4 (less than or equal to 0.4) Non-polar covalent Atoms share electrons fairly equally Between 0.5 to 1.9 Polar covalent Atoms share electrons, but the “stronger” one pulls the electrons closer ≥2.0 (greater than or equal to2.0) Ionic One atom is so “strong” that it pulls the electron completely away from the other atom.

Use the electronegativity table on pg. 241 to determine if the following bond are… Polar covalent Polar covalent Non-polar covalent Non-polar covalent Ionic Ionic H-O H-O N-Br N-Br Na-Cl Na-Cl K-F K-F Cl-Cl Cl-Cl

Naming Covalent Compounds Learn the following prefixes Learn the following prefixes 1. Mono- 2. Di- 3. Tri- 4. Tetra- 5. Penta- 6. Hexa- 7. Hepta- 8. Octa- 9. Nona- 10. Deca-

Naming Rules The first word is just the name of the atom. The first word is just the name of the atom. If there is more than one of the first atom, use a prefix. If there is more than one of the first atom, use a prefix. The second word ALWAYS has a prefix and ends in –ide. The second word ALWAYS has a prefix and ends in –ide.

Examples 1. NO 3 2. PF 5 3. SO 2 4. BCl 3 5. N 2 O 4 * If adding a prefix gives you “oo” or “ao”, drop the first vowel.

Common Acids Acid: a molecular substance that, when dissolved in water, produces H+ ions Acid: a molecular substance that, when dissolved in water, produces H+ ions Take the polyatomic, whatever the number is of its charge, put that many “H”s at the beginning Take the polyatomic, whatever the number is of its charge, put that many “H”s at the beginning Hydrochlor ic HCl Acetic HC 2 H 3 O 2 Nitric HNO 3 Carbonic H 2 CO 3 Sulfuric H 2 SO 4 Phosphoric H 3 PO 4

Hydrates: Ionic compounds that absorb water into their solid structures Ionic compounds that absorb water into their solid structures Named as Xhydrates, where the X is the number of water molecules Named as Xhydrates, where the X is the number of water molecules Ex: CuSO 4 · 5 H 2 O Ex: CuSO 4 · 5 H 2 O Copper (II) sulfate pentahydrate Copper (II) sulfate pentahydrate