1. Chapter 2.3-2.4 By: Sarah Pressl Cindy Tran Nick Puleo Nelson Le

2. Summary Atoms are held together by chemical bonds Strongest are covalent and ionic Covalent bonds occur when atoms share a pair of electrons Nonpolar and polar Ionic bonds occur when atoms share electrons but one is more electronegative Ionic compound=salt Weak bonds allow large molecules to function Ex. hydrogen bonding Van der Waals interactions occur in “hot spots” of opposite charges Shape of a molecule will determine how it interacts Chemical reactions create and destroy chemical bonds Equilibrium occurs with a ratio products and reactants

3. Ionic Bonding

4. Questions • Analyze the covalent bond and create a situation in which two atoms are bonded covalently. • Justify the purpose of a valence electron in an atom. • Distinguish the differences between nonpolar covalent bonds and polar covalent bonds. • Give a situation in which weak bonds are important in living organisms. • Relate why hydrogen bonds and van der Waals interactions are weak. • Interpret the meaning of electronegativity in your own words. • What are also considered ionic bonds? • Evaluate the importance of coefficients in a chemical reaction. • Distinguish the difference between reactants and reaction. • Based on the definition of a reaction, what importance does it have in the biological world? • Analyze why it is impossible for a reaction to reverse. • Evaluate the importance of a chemical equilibrium when it occurs.

5. Clarification • “…form a molecule by sharing two pairs of valence electrons. The atoms are thus joined by what is called a double covalent bond, or simply a double bond.” • A molecule needs two unpaired electrons to form a double bond with another molecule that has two unpaired electrons • “A hydrogen bond forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative. • Hydrogen bonding occurs when a hydrogen molecule is near a molecule with an anion • “These van der Waals interactions are weak and only occur when atoms and molecules are very close together.” • Electrons are in constant motion and tend to build up in oppositely charged areas of the molecule leading to weak, temporary bonds • “The point at which the reactions offset one another exactly is called chemical equilibrium.” • When forward and reverse reactions occur at the same time, a chemical equilibrium will be formed • “The attraction of a particular kind of atom for the electrons of a covalent bond is called electronegativity.” • If the electronegativity increases to where one atom is more electronegative, it will strip the other atom of its outermost electron

6. Predictions • Molecule: • Ch.2-two or more atoms held together by covalent bonds • Ch.7-used in membrane structure and function, phospholipids and proteins arranged in a membrane of cells • Reactants: • Ch.2-starting materials in a chemical reaction • Ch.8-used in an intro to metabolism, chemical work: phosphorylates • van der Waals interactions: • Ch.2-“hot spots of positive & negative charge that allow atoms to stick together • Ch.5-used in structure and function of macromolecules, used in hydrophobic interactions • Sodium Chloride (salts): • Ch.2-compouds formed by ionic bonds • Ch.42-used in animal nutrition • Ion: • Ch.2-a charged atom or molecule • Ch.11-used in cell communication

7. Acknowledgements All pictures were obtained via the Campbell Reece AP Edition Biology Seventh Edition textbook.