The Chemical Context of Life Chapter 2 The Chemical Context of Life Students -Test corrections due tomorrow – my error from yesterday  -Transport - next Tuesday -Tossing 1 question: For corrections, write “Question tossed” A – 27, B – 5 Learning Log mid-point check: Next Thursday – Ch 2 & 3 -Costa Rica trip info -Cell phones in bin – ON SILENT OR OFF!!!!!!!

Chapter 2 The Chemical Context of Life 1. What is the hierarchy of life? (smallest to largest)

6 Organs and organ systems 7 Tissues 10 Molecules 8 Cells 6 Organs and organ systems 7 Tissues 10 Molecules 9 Organelles 50 µm 10 µm 1 µm Cell Atoms

Figure 1.3 Exploring Levels of Biological Organization 1 The biosphere 2 Ecosystems 3 Communities 4 Populations 5 Organisms

Chapter 2 The Chemical Context of Life What is the hierarchy of life? (smallest to largest) What is an atom? Smallest unit of matter that retains the physical & chemical properties of its element Element – a substance that cannot be broken down into other substances by chemical rxn What is an atom made of? Proton – (+1) charge, found in nucleus, 1 amu Neutron – no charge, found in nucleus, 1 amu Electron – (-1) charge, orbit nucleus, mass negligible

Figure 2.4 Simplified models of a helium (He) atom Cloud of negative charge (2 electrons) Electrons Nucleus (a) (b)

Chapter 2 The Chemical Context of Life What is an atom? What is an atom made of? What do these numbers mean? 23Na 12C 11Na 6C What is an isotope? Radioisotope? Atoms of an element that have the same atomic # but different atomic mass Unstable isotope where the nucleus spontaneously decays emitting subatomic particles &/or energy as radioactivity. 5. What are radioisotopes used for? Atomic mass - protons + neutrons Atomic # - # of protons

Chapter 2 The Chemical Context of Life What is an atom? What is an atom made of? What do these numbers mean? What is an isotope? Radioisotope? What are radioisotopes used for? How are atoms held together? What are the different types of strong bonds? Covalent – sharing of electrons Polar covalent – UNequal sharing Non-polar covalent – equal sharing Ionic – complete transfer of electrons bonds

Chapter 2 The Chemical Context of Life What is an atom? What is an atom made of? What do these numbers mean? What is an isotope? Radioisotope? What are radioisotopes used for? How are atoms held together? What are the different types of strong bonds? What is electronegativity? Atom’s ability to attract & hold electrons In Biology – most concerned with N & O

Formation of a covalent bond Hydrogen atoms (2 H) Hydrogen molecule (H2) + In each hydrogen atom, the single electron is held in its orbital by its attraction to the proton in the nucleus. 1 When two hydrogen atoms approach each other, the electron of each atom is also attracted to the proton in the other nucleus. 2 The two electrons become shared in a covalent bond, forming an H2 molecule. 3 Figure 2.10

Single and double covalent bonds Name (molecular formula) Electron- shell diagram Structural formula Space- filling model Hydrogen (H2). Two hydrogen atoms can form a single bond. Oxygen (O2). Two oxygen atoms share two pairs of electrons to form a double bond. H O Figure 2.11 A, B (a) (b)

Covalent bonding in compounds Name (molecular formula) Electron- shell diagram Structural formula Space- filling model (c) Methane (CH4). Four hydrogen atoms can satisfy the valence of one carbon atom, forming methane. Water (H2O). Two hydrogen atoms and one oxygen atom are joined by covalent bonds to produce a molecule of water. (d) H O C Figure 2.11 C, D

In a polar covalent bond The atoms have differing electronegativities Share the electrons unequally This results in a partial negative charge on the oxygen and a partial positive charge on the hydrogens. H2O d– O H d+ Because oxygen (O) is more electronegative than hydrogen (H), shared electrons are pulled more toward oxygen. d– Figure 2.12

Sodium chloride (NaCl) An ionic bond Is an attraction between anions and cations Due to high electronegativity Cl– Chloride ion (an anion) – The lone valence electron of a sodium atom is transferred to join the 7 valence electrons of a chlorine atom. 1 Each resulting ion has a completed valence shell. An ionic bond can form between the oppositely charged ions. 2 Na Cl + Sodium atom (an uncharged atom) Chlorine atom Na+ Sodium on (a cation) Sodium chloride (NaCl) Figure 2.13

Hydrogen Bonds A hydrogen bond Occurs between 2 molecules with polar covalent bonds Forms when a hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom  –  + Water (H2O) Ammonia (NH3) O H  +  – N A hydrogen bond results from the attraction between the partial positive charge on the hydrogen atom of water and the partial negative charge on the nitrogen atom of ammonia. + d+ Figure 2.15  +

Molecular shape Determines how biological molecules recognize and respond to one another with specificity

Figure 2.17 Carbon Nitrogen Hydrogen Sulfur Oxygen Natural endorphin Morphine Carbon Hydrogen Nitrogen Sulfur Oxygen Natural endorphin (a) Structures of endorphin and morphine. The boxed portion of the endorphin molecule (left) binds to receptor molecules on target cells in the brain. The boxed portion of the morphine molecule is a close match. (b) Binding to endorphin receptors. Endorphin receptors on the surface of a brain cell recognize and can bind to both endorphin and morphine. Endorphin receptors Brain cell Figure 2.17

Chapter 2 The Chemical Context of Life What is an atom? What is an atom made of? What do these numbers mean? What is an isotope? Radioisotope? What are radioisotopes used for? How are atoms held together? What are the different types of strong bonds? What is electronegativity? How are bonds created between atoms?

What is chemical equilibrium? Chemical reactions Convert reactants to products Reactants Reaction Product 2 H2 O2 2 H2O + What is chemical equilibrium?

Chemical equilibrium Is reached when the forward and reverse reaction rates are equal