CHAPTER 6: THE CHEMISTRY IN BIOLOGY 6.1 CHEMICIAL BONDS CHAPTER 6: THE CHEMISTRY IN BIOLOGY

Aim: differential between the different types of bonds

COMPOUNDS Elements can undergo chemical reactions to combine with other elements in order to become stable. Stable elements have their outer energy level filled-meaning they have 8 electrons

CHEMICAL BONDS The force that holds atoms together is known as a chemical bond. Electrons are directly involved in the formation of chemical bonds. -They travel around the nucleus of an atom in areas called energy levels. -Each energy levels has a specific number of electrons that it can hold at any time -The first energy level which is closest to the nucleus can hold up to 2 electrons. -The second energy level can hold 8 electrons.

TYPES OF CHEMICAL BONDS I. Covalent bonds II. Ionic bonds

Covalent bonds - Covalent bond—forms when atoms share one or more pairs of electrons A molecule is a compound in which the atoms are held together by covalent bonds. Occur in only nonpolar elements Can be a single, double, or triple bond depending on number of pairs of electrons shared. There are 2 types: 1. Nonpolar Covalent - equal sharing of electrons 2. Polar Covalent- unequal sharing of electrons

covalent bonds

Covalent Bond

Ionic Bonds Ionic Bond—forms when atom gives up electrons and another receives electrons in order to become stable Electrical attraction between two oppositely charged atoms or groups of atoms called ions. Most ionic compounds are crystalline at room temperature and have higher melting points than molecular compounds formed by covalent bonds.

Ionic Bonds Sodium and Chlorine -both atoms are unstable -to become stable, sodium gives away 1 electron and becomes positive, chlorine receives 1 electron and becomes negative

Ionic bonds

Ionic bonds Some atoms tend to donate or accept electrons more easily than other atoms. The elements identified as metals tend to donate electrons. The elements identified as nonmetals tend to accept electrons.

ionic bonds

Van der waals forces Defined as the attraction between molecules This occurs when molecules come close together, and the attractive forces between slightly positive and negative regions pull on the molecules and hold them together. The strength of the attraction depends on the size of the molecule, its shape, and its ability to attract electrons Important in biological processes.

Van der waals forces

The end Tomorrow’s lecture will be on activation energy and enzymes