The Chemical Context of Life: Chemical Elements and Compounds
Atom: the smallest unit of an element that still retains the property of the element. Atoms are made up of neutrons, protons, and electrons
Mass Number: the number of protons and neutrons
Atomic Number: The number of protons an element possesses
• Hydrogen bonds are weak
• Covalent bonds share valence electrons (metal to metal)
• Ionic bonds oppositely charged ions (metal to nonmetal)
• Structural formula shares bonds
• Polar and nonpolar
- Atoms and Molecules
- Chemical Bonds are defined as interactions between the valence electrons of atoms, and atoms are held together by chemical bonds to form molecules
- A covalent bond occurs when valence electrons are shared by two atoms
- Nonpolar covalent bonds occur when the electrons being shared are shared equally between the two atoms.
- In polar covalent bonds, the two atoms have different electronegatives, resulting in an unequal sharing of the electrons.
- Ionic bonds are ones in which the two bonded atoms attract the shared electrons so unequally that the more electronegative atom steals the electron away form the less electronegative atom. Ionic bonds form ionic compounds or salts.
I. The Importance of Carbon
- Organic chemistry is the branch of chemistry that specializes in the study of carbon compounds
- The carbon atom
- Usually has an atomic number of 6; therefore, it has 4 valence electrons
- Usually completes its outer energy shell by sharing valence electrons in four covalent bonds; tetravalent electron configuration
- Covalent bonds link carbon atoms together in long chains that form the skeletal framework for organic molecules. These carbon skeletons may vary in:
ii. Shape (straight, chain, branched, ring)
iii. Number and location of double bonds
iv. Other elements covalently bonded to available sites
- Hydrocarbons are made containing only carbon and hydrogen
- Isomers are compounds with the same molecular formula but with different structures and hence different properties. Isomers are a source of variation among organic molecules.
- There are three types of isomers
~Structural isomers are isomers that differ in the covalent arrangement of their
*Same molecular formula, skeleton may change and can differ in location of
~Geometric isomers are isomers that share the same covalent partnerships, but
differ in their spatial arrangement.
*Double bonds are inflexible
** Don't forget that Chapter 4 Vocabulary is due tomorrow and that there is a quiz on Chapter 2. Also, test corrections are due Thursday, but Mrs. Lyon will take them Friday too.