VTT 200 General Sciences Chemistry Chemical Bonding & Molecules Coville Ch. 2 pp. 17-20

Chemical Bonding A second Law of Einstein… “Everything in the universe strives for balance and stability” Atoms are stable when their outer most shell or energy level is full.

Chemical Bonding & Molecules Atoms link together in different combinations and arrangements called compounds. Links between atoms are chemical bonds. Atoms form bonds based on the electrons in their outer shell (AKA Valence electrons).

The key is the Valence Shell Chemical bonds tend to form so that each atom (by gaining, losing, or sharing one or more electrons) has its outermost shell full or shared full. Shells 2-3 will have 8 electrons if full Shell 4 will have 18 electrons if full

Covalent Bonding—p. 17 This is when atoms share (valence) electrons to become stable. This is the strongest type of bond; atoms bonded this way function as one unit This unit (molecule) is very difficult to break apart

Covalent Bonding-Shared electrons In the above example, each H atom has 1 valence electron—however, 2 electrons would fill the valence shell—by sharing the electrons, each H atom “believes” its outer shell is full

Covalent Bonding Atoms will strive to share electrons so that the valence shells appear full Look at the example of O2 on page 16 1 pair of shared electrons is a single bond. 2 pairs of shared electrons is a double bond. 3 pairs of shared electrons is a triple bond. (The more electrons shared, the stronger the bond) **Such bonding can be indicated with a shorthand using line drawings between atoms: EX: H-H (single bond between two hydrogen atoms) O=C=O (double bond from each Oxygen atom; notice the Carbon atom has 4 total bonds) Review back to the drawings in the text on p. 16

Ionic Bonds- complete transfer of electrons Let’s review what makes an ion…when an atom loses or gains electrons, its net electrical charge changes The opposing electrical charges (+) and (-) attract the atoms together and hold them. See the example on p. 17 and below Important NOTE: the ions are formed BEFORE they are attracted to each other

Hydrogen Bonding The weakest type of bond. When a hydrogen atom shares an electron with another atom, the hydrogen atom has a slight positive charge This slight positive is attracted to a slight negative of another atom. Water molecules form hydrogen bonds.

Water in Various States Examples of relationship of Hydrogen & Polar Bonding As liquid, hydrogen bonds are lax and fluid, that is water moving Under 32° F water freezes, bonds become rigid and structured Over 210° F water vaporizes, bonds break apart and individual water molecules float apart Transparency of water & ice; looking through hydrogen bonds

Chemical Reactions & Equations; . Pp. 20-21 What types of chemical reactions are discussed in your text? Another law of Einstein: Conservation of Matter: in a chemical reaction, matter can neither be created nor destroyed—atoms must be accounted for This is why equations must be balanced

Balancing Chemical Equations A reaction/ equation has two sides: -Reactants are on the left of the arrow -Products are to the right of the arrow The arrow does not mean equals, but Yields EX: 2 Hydrogen atoms + 1 Oxygen atom > 1 molecule of H2O See handout on balancing equations by counting atoms