Basic Chemistry
Atoms Smallest particles that retain properties of an element Made up of subatomic particles: Protons (+) Electrons (-) Neutrons (no charge)
Examples of Atoms electron proton neutron Hydrogen Helium
Isotopes Atoms of an element with different numbers of neutrons Behave the same way in chemical reactions Radioisotopes emit particles and energy as they decay, eventually becoming a different element
Isotopes of hydrogen
Mass Number Number of protons + Number of neutrons H = 1 P +, 0 N 0 atomic mass = 1 C = 6 P +, 6 N 0 atomic mass = 12 Hydrogen 1p+, 1e _, 0N 0 Carbon 6p+, 6e, 6N 0
Electrons Carry a negative charge Repel one another Are attracted to protons in the nucleus Move in orbitals (volumes of space that surround the nucleus)
Electron Orbitals Orbitals can hold up to two electrons Atoms differ in the number of electrons in orbitals Orbitals closest to nucleus are lower energy and are filled first
Shell Model First shell Lowest orbital Holds 2 electrons Second shell 4 orbitals hold up to a total of 8 electrons Unfilled shells make atoms likely to react
The Shell Model sodium 11p +, 11e chlorine 17p +, 17e carbon 6p +, 6e oxygen 8p +, 8e neon 10p +, 10e hydrogen 1p +, 1e helium 2p +, 2e electron proton neutron Fig. 2-2, p.17
Electron First electron shell can hold 2 electrons Outer electron shell can hold 8 electrons Hydrogen H Atomic number = 1 Carbon C Atomic number = 6 Nitrogen N Atomic number = 7 Oxygen O Atomic number = 8 Figure 2.5
What Determines Whether Atoms Will Interact? The number and arrangement of their electrons
Chemical Bonds, Molecules, and Compounds Bond is union between electron structures of atoms Atoms bond to form molecules Molecules may contain atoms of only one element: O 2 Compounds contain more than one element: H 2 O
Important Bonds in Biological Molecules Ionic bonds Covalent bonds Hydrogen bonds
ionic hydrogen covalent How atoms bond
Ionic Bonding One atom loses electrons, becomes positively charged ion Another atom gains these electrons, becomes negatively charged ion Charge difference attracts the two ions to one another
Sodium atom (Na) Outer shell has one electron Chlorine atom (Cl) Outer shell has seven electrons Na transfers electron to Cl, forming Na + and Cl - Ions remain together as NaCl (sodium chloride) Formation of NaCl
NaCl Fig. 2-3a, p.18
Covalent Bonding Atoms share a pair or pairs of electrons to fill outermost shell Single covalent bond Double covalent bond Triple covalent bond Molecular hydrogen
Single Bond Molecular Hydrogen (H 2 ) Oxygen Molecular (O) Oxygen (O 2 or O=O) Double Bond Triple Bond Molecular Nitrogen (N 2 or NΞN)
Two hydrogen atoms, each with one proton, share two electrons in a single covalent bond that is nonpolar molecular hydrogen (H H) Two oxygen atoms, each with eight protons, share four electrons in a double covalent bond, also nonpolar. molecular oxygen (O=O) water (H O H) Two hydrogen atoms each share an electron with oxygen. The resulting two covalent bonds form a water molecule. These bonds are polar. The oxygen exerts a greater pull on the shared electrons, so it bears a slight negative charge. Each hydrogen bears a slight positive charge. Fig. 2-3b, p.19
Polar or Nonpolar Bonds Nonpolar if atoms share electrons equally Hydrogen gas (H - H) Polar if electrons spend more time near nucleus with most protons Water Electrons more attracted to O nucleus than to H nuclei
Water Is a Polar Covalent Molecule Molecule has no net charge slight negative charge on the oxygen atom ( ) O Oxygen end has a slight negative charge (+) H H (+) Hydrogen end has a slight positive charge slight positive charge on each hydrogen atom Fig. 2-4b, p.20
Hydrogen Bonding Atom in one polar covalent molecule is attracted to oppositely charged atom in another such molecule or in same molecule Water molecule Ammonia molecule
hydrogen bond water molecule ammonia molecule Two molecules interacting in one hydrogen (H) bond. H bonds helping to hold part of two large molecules together. Many H bonds hold DNA s two strands together. Individually, each H bond is weak, but collectively they stabilize DNA s large structure. Fig. 2-3c, p.19
Hydrogen Bonding in DNA
Properties of Water Polarity Stabilizes temperature Adhesion Cohesion Capillarity Capacity to dissolve substances
Polarity Hydrophilic substances Polar covalent bond Hydrogen bond with water Example: sugar Hydrophobic substances Nonpolar covalent bond Repelled by water Example: oil
Temperature-Stabilizing Effects Liquid water can absorb much heat before its temperature rises Energy first disrupts hydrogen bonding before increasing the movement of molecules
Evaporative Cooling As energy causes molecules to break free, they carry away some energy Evaporative water loss is used by mammals to lower body temperature
Cohesion and Evaporation
Water Adhesion Hydrogen bonding holds polar molecules together Water Ammonium
Capillarity Water climbs narrow tubes Adhesive Force Cohesive Force
Spheres of Hydration Water forms hydrogen bonds Fig. 2-5, p.21
Hydrogen Ions: H + Unbound protons Important biological functions Form when water ionizes
The ph Scale Measures H + concentration of fluid Change of 1 on scale means 10X change in H + concentration Highest H + Lowest H + 0---------------------7-------------------14 Acidic Neutral Basic
Fig. 2-7, p.22
Examples of ph Pure water is neutral with ph of 7.0 Acidic Stomach acid: ph 1.0 3.0 Lemon juice: ph 2.3 Basic Seawater: ph 7.8 8.3 Baking soda: ph 9.0
Acids Acids and Bases Donate H + when dissolved in water Acidic solutions have ph < 7 Bases Accept H + when dissolved in water Acidic solutions have ph > 7
Buffer System Minimizes shifts in ph Is a partnership between a weak acid and the base it forms when dissolved The weak acid and base work as a pair to counter shifts in ph
Carbonic Acid Bicarbonate Buffer System When blood ph rises, carbonic acid dissociates to form bicarbonate and H + H 2 CO 3 -----> HCO 3- + H + When blood ph drops, bicarbonate binds H + to form carbonic acid HCO 3 - + H + -----> H 2 CO 3
Salts Compounds that release ions other than H + and OH - when dissolved in water Example: NaCl releases Na + and Cl Many salts dissolve into ions that play important biological roles