Lecture 2: Molecules and Bonds Flashcards
Understand how valence electrons participate in covalent bond formation.
Valence electrons that are unpaired in the highest energy level are able to participate in covalent bonding.
Given the periodic table, be able to predict how many bonds an element can form.
First column has one valence electron. Second column has two valence electrons. Second to last column has seven valence electrons. Third to last column has six valence electrons. Fourth to last column has five valence electrons.
Be able to distinguish the types of strong bonds (covalent) based on electronegativity.
Non-polar covalent bonds have electrons shared nearly equally around the bond. Both atoms are either both very electronegative or both not very electronegative. The electronegativity different is less than 0.5.
Polar covalent bonds are unequally shared around the bond. One atom must be very electronegative and one atom not very electronegative. The electronegativity difference is between 0.5 and 1.4 and it creates a dipole moment.
Differentiate strong bonds from weak bonds (charge interactions).
Weak bond can break and form more easily without enzymes. Strong bonds are more permanent and require an enzyme in order to be broken. Strong bonds involve electron sharing; weak bonds only involve electrostatic attraction.
Be able to distinguish types of weak bonds (ionic, hydrogen, hydrophobic/van der waals).
Ionic bonds are charged interactions between one negatively charged ion and one positively charged ion..
Hydrogen bonds are charged attractions between a lone pair of electrons on an electronegative atom and a hydrogen that is bonded covalently to another strongly electronegative atom. Hydrogen = donor; Electronegative atom = acceptor (N or O).
Know what elements can participate in hydrogen bonding.
Nitrogen and oxygen can participate in hydrogen bonding.
Understand why dynamic living systems depend on weak bond interactions.
Weak bonds break and form without the use of enzymes and take less energy to do. Covalent bonds need enzymes and use a lot of energy to break and form. If a weak bond is mutated, a protein and ligand can still interact because there are many weak bonds helping them to interact.
Know how hydrogen bonding influences the properties of water: heat capacity, cohesion, density, and hydration.
Water can form a hydrogen bond network with itself. Stronger bonds require more energy to break. Water has a high heat capacity. When water molecules break off, they tend to bring other water molecules with them due to cohesion. Water has a density of 1000mg/kg. When water is frozen, it expands its network. If the cell freezes, water expands, and the cell bursts. Water is able to hydrate itself. Water dissolves polar solutions and surrounds non-polar solutions. Water hydrates ionic bonds and makes them weaker (NaCl).
Be able to predict the behavior of hydrophilic, hydrophobic, and amphipathic substances in water.
Hydrophobic molecules are non-polar and will aggregate away from water.
Hydrophilic molecules are water loving and will form ionic or hydrogen bonds with water.
Amphipathic molecules have both hydrophobic and hydrophilic parts.
Understand how autohydration of water is related to pH.
Water is able to hydrate itself. It forms hydronium ions. When broken back down into H2O and a proton, the proton determines the pH.
Be able to roughly estimate the pH of various common materials.
pH=-log[H+]
Blood has a pH of about 7.4.
