Understanding Chemical Bonds and Reactions: Molecules and Compounds

1. Molecules Compounds Chemical Reactions

2. Molecules • two or more of same or different elements chemically combine H (atom) +H (atom) H2 (molecule)

3. Compounds • two or more different atoms combine together to form a molecule called a compound 4H (atoms) + C (atom) CH4 (molecule) (methane)

4. Chemical Reactions • when atoms combine or dissociate from other atoms: - new products are formed - chemical reactions are foundation of all life processes Chemical Bonds • formed when atoms unite chemically

5. Bond Formation • energy relationship (not physical) • involves reactions between electrons of reacting atoms • electrons in outermost shell are most important in bonding

6. Electrons • occupy specific regions in rotation around the nucleus of an atom • these regions vary in distances from the nucleus • each orbit around nucleus represents one electron shell or energy level

7. Electrons (cont.) • each shell holds a certain maximumnumber of electrons • innermost shell nearest nucleus never holds more than 2 electrons • second shell holds 8 (rule of 8’s) • third 18 • higher shells (7) hold many more electrons

8. Stability • atoms will react to maintain 8 electrons in their valence shell (except shell one which is full at 2 electrons) • if valence shell has less than 8 electrons the atom will gain, loose, or share electrons to remain stable

9. Electrons • electrons in energy level closest to nucleus are most strongly attracted to its +charge • electrons farthest from nucleus or + charge are most likely to react with other atoms

10. Bonding • most important electrons are those in outermost shell (valence shell) • inner shells do not necessarily take part in bonding

11. Types of Chemical Bonds

12. Ionic Bonds • formed when electrons are completely transferred from one atom to another • during bonding atoms gain or loose electrons • therefore atoms are no longer neutral • now called ions

13. Ions • are atoms that have gained or lost electrons • negatively or positively charged particles • Two types of ions: - anion(-) atom that has gained electrons - cation (+) atom that has lost electrons

14. Electrolytes • are ions in solution • ionic solution is capable of conducting electrical current

15. Sodium(atomic number = 11) • valence shell has 1 electron • incomplete • if 1 electron is lost it will have more protons than electrons • +charge • cation

16. Chlorine(atomic number = 17) • valence shell has 7 electrons • incomplete, needs one electron to fill valence shell • if 1 electron is gained it will have more electrons than neutrons • -charge • anion

17. Ionic Bond - Sodium Chloride • sodium tends to give up its single electron in its valence shell • chlorine will pick up one electron to completely fill its valence shell

18. Covalent Bonds

19. Covalent Bonds • bonds in which atoms share electrons • more common bond in the body than ionic • electrons of combining atoms are neither lost or gained • electrons are shared

20. Single Covalent Bond H2 (H H) • when two atoms share one pair of electrons (H-H) • valence electrons are shared • shared electrons orbit whole molecule and satisfy stability needs of both hydrogen atoms

21. Double Covalent Bond Oxygen (O O) • occurs when two atoms share two pairs of electrons

22. Triple Covalent Bond Nitrogen (N N) • occurs when three pairs of electrons are shared

23. Nonpolar Covalent Bonds • electrons are shared equally between two atoms • strongest of all chemical bonds • electrons spend approximately equal time around each nucleus • Example: - carbon:carbon, and hydrogen:hydrogen bonds are nonpolar covalent

24. Polar Covalent Bonds • unequal sharing of electrons between atoms • one atom attracts shared electrons more strongly than the other • Example: - hydrogen and oxygen in a molecule of water

25. Hydrogen Bonds • attraction between partially (-) or (+) charged atoms • Examples: - exist between adjacent H2O molecules - between polarized regions of same large molecules (protein) - between two strands of a DNA molecule

26. Chemical Reactions

27. Chemical Reactions • involved in making or breaking bonds between atoms • new bonds are formed • total amount of atoms remains the same • new arrangement or combination

28. Synthesis Reaction(anabolism) • two or more molecules or reactants bond together to form larger complex molecule • involve bond formation • energy-requiring reaction • growth/constructive • repair

29. Synthesis Reaction(anabolism) • A + B AB • 2H + O H2O

30. Decomposition Reaction(catabolism) • molecule is broken down into smaller parts • synthesis reaction in reverse • energy is released • destructive • Example: - digestion of foods into building blocks

31. Decomposition Reaction(catabolism) • AB A+B • NaCl Na+ + Cl-

32. Exchange Reaction • involve synthesis and decomposition reactions • bonds are made and broken • molecule parts switched

33. Exchange Reaction • AB + CD AD + CB • Example: - iron-containing complex in RBC unloads carbon dioxide and picks up oxygen in lungs.