Biology I Covalent Bonds 3.00_Chemistry of Biology Biology I Covalent Bonds Slides 132-145

Covalent Bonding

Chemistry: What is a Covalent Bond? (Polar and Nonpolar) https://www.youtube.com/watch?v=ZxWmyZmwXtA

Polar Covalent Bonds https://www.youtube.com/watch?v=15NvvwuTr5E

Covalent Bonding Chemical bond that forms when electrons are shared. Most compounds in living organisms have covalent bonds holding them together. A molecule is a compound in which the atoms are held together by covalent bonds. Depending on the number of pairs of electrons that are shared, covalent bonds can be single (H2), double (O2), or triple (N2).

Covalent Bond Covalent bonds occur when 2 atoms share a pair of electrons. The electrons spend part of their time with both atoms, so the octet rule is satisfied sufficiently. A molecule of hydrogen gas, H2, has 2 hydrogen atoms. Each atom provides 1 electron, so in the bond each atom shares 2, a complete shell for hydrogen. The bond is symbolized as a line connecting the 2 H’s: H-H In water (H2O), the oxygen has 6 electrons in its outer shell, and it shares one with each of the 2 hydrogens, giving 8 shared electrons for oxygen and 2 for each hydrogen. Covalent bonds are the most common type in biological molecules. 6

Covalent Bonding Occur when electrons are SHARED by atoms. These new structures that result from covalent bonds are called MOLECULES ** In general, the more chemical bonds a molecule as the more energy it contains SHARING IS CARING!

Chlorine atom 2,8,7 2 Chlorine atoms Outer shells only Chlorine molecule Cl2 Electrons shared Each outer shell has 8 electrons Forces (bonds) between atoms in the molecule very strong Forces between molecules very weak Molecular or covalent compounds are usually gases or liquids – they have low melting points and low boiling points Molecules have no overall electric charge

Chlorine Cl2 Cl Cl Cl Cl

Covalent bonds- Two atoms share one or more pairs of outer-shell electrons. Oxygen Atom Oxygen Atom Oxygen Molecule (O2)

Covalent Bonds: Water H2O Methane CH4 Ammonia NH3 Hydrogen H2 Hydrogen Chloride HCl Oxygen O2 N.B. Oxygen has a double bond

2 Oxygen atoms (outer shells only) Oxygen O 16 8 Double covalent bond O

Covalent bonds can be represented in 3 ways:

Covalent Bonding Covalent bonds: a covalent bonds forms when two atoms share a pair of electrons together ( thus each atom will be donating an electron to form the bond) .If each atom donates 2electrons a double bond is formed which is stronger and more rigid, and a triple bond is formed when 3electrons is donated by each atom. It is the strongest chemical bond. It can be a non-polar covalent bond, which arises when the two atoms involved are of the same element thus having the same electronegativity thus share the pair of electrons equally. Non-polar covalent bond