* What is a compound and how is it different than an element? Compound is more than one element. An element cannot be broken down by chem. Rxns. * What are the 4 main elements of life? Why?
C,H,O,N they make up 96% of living matter and they are found in all of the major macromolecules * Be able to calculate the number of protons, neutrons and electrons given an element’s mass number or atomic number. If given this symbol - 4He – can you tell me how many neutrons and protons there are? If given this symbol 12Na – can you tell me how many neutrons and protons there are? Does this element exist? * What is an isotope?
2 atoms of the same element that differ in # neutrons
* How are electrons arranged in an atom? Are they paired or unpaired? Which electrons make an element reactive? * How many electrons can reside in each electron shell (first, second and third)? * What are valence electrons and why are they important? * What is valence? What is the valence of carbon, nitrogen, oxygen and hydrogen? This information will not be given to you on the exam and therefore you must know this! * Be able to name the five types of bonds (covalent (2 types), ionic and weak chemical bonds (2 types)). What needs to happen for each of these bonds to be created? For example, for a covalent bond electrons must be shared equally between two elements and these elements will share unpaired valence electrons. Polar covalent unequal sharing of electrons, nonpolar covalent equal sharing of electrons, ionic transfer of electrons, H-bond between H and O/N/F inter- or intra-molecularly because of the partially positive charge of H and the partially negative charge of O/N/F, Van der Waals between neutral atoms with partially charged regions due to asymmetric electron accumulation by chance. The atoms/molecules must be very close together * What are their similarities and differences?
* What happens when a polar covalent bond is formed? Why do polar covalent bonds occur? Electrons are shared unequally. There is a dipole moment and partially positive/negative regions of the molecule because the atoms have different electronegativities. * What happens when an ionic bond is formed? Why do ionic bonds occur? There is a transfer of electrons from a metal to a nonmetal that creates a cation and an anion respectively. The transfer occurs because each atom seeks to have a stable electron configuration.
* Be able to draw 4 water molecules interacting through hydrogen bonding – include partial positive and negative charges on the correct atoms * Why does hydrogen bonding between water molecules enable: 1. Cohesion – what does this term mean?
As a result of H-bonding, H2O molecules stay close to ea. other. Ex: transport of water and dissolved nutrients against gravity in plants Adhesion: water adheres to other substances such as a cell wall High surface tension
2. Moderation in Temperature
High Cp. Absorbs heat from air and releases stored heat into cooler air. Can absorb/release a lot of heat w/o drastically changing its own temp. High heat of vaporization b/c of strength of H-bonds
3. Ice to float
The H-bonds keep H2O molecules a distance away from ea. other when they freeze = ice less dense. 4. Solutes to be dissolved and aqueous solutions to be formed Because of the partially neg and pos regions in H2O, it can attract both cations and anions. It forms a hydration shell by completely surrounding ions and separating them from ea. other. Nonionic polar molecules can also be dissolved b/c water forms H-bonds with them
* What is a solute compared to a solvent?
Solute is dissolved in solvent (the most abundant substance) * Be able to define “hydrophilic” and “hydrophobic.” Water loving (polar) and water fearing (nonpolar)
* What is a mole? What is molarity? Are these two terms related? How? A mole is the amount of substance in...