1. Unit 2: All Biology is Chemistry Lesson 2: The Chemistry of Life

2. Drill 30 September 2008 Look at the chemical symbols to the left. 1.Name each element. 2.Which element is most abundant in the human body? Least abundant? 3.Which element(s) are major elements for the human body? 4.Be prepared to share information about the trace element you researched for homework. OVCSeNH

3. Objectives At the conclusion of this lesson students will be able to: 4.Explain the relationship between elements and atoms.elements atoms 5.Identify and compare the charge, mass, and location of subatomic particles.subatomic particles 6.Draw and label a Bohr model of the structure of the atom.Bohr model 7.Be able to calculate the mass number of an atom.mass number 8.Define isotope and explain two of their uses in biology.isotope

4. The Atom – The Simplest of Particles The atom is the simplest particle of an element that retains the properties of that element.atom –From Greek word “atomos” meaning “unable to be cut.” Obj. 1 Obj. 1

5. The Structure of an Atom Bohr Model – “planetary model” Proposed by Niels Bohr in 1915 A useful approximation of the structure of an atom. Consists of two parts: A central region, or nucleus Electron cloud – composed of orbitals or three-dimensional regions around a nucleus

6. The Bohr Model Below is a Bohr Model of a helium (He) atom. n + n + Nucleus 2 protons neutrons 2 neutrons Electron cloud Consists of orbitals where high-energy electrons orbit the nucleus

7. Subatomic Particles Protons Positively (+) charged particles Have mass (1 amu = 1 atomic mass unit) Located in the nucleus + Neutrons Neutral particles (No charge) Have mass – 1 amu Also located in the nucleus n Electrons Negatively (-) charged particles Mass is negligible (1/1840 amu) Remain in constant motion in orbitals Obj. 3 Obj. 3

8. Another Look at the Periodic Table 6 C 12.011 Atomic Number

9. Atomically Speaking… The number of protons in an atom is called the atomic number. In an atom, the number of positive protons is balanced by an equal number of negative electrons. –net electrical charge equals zero The Bohr model to the left represents an atom of which element? How many electrons must be in the electron cloud? = neutron= proton

10. Atomically Speaking… The mass number of an atom is equal to the total number of protons and neutrons of the atom. What is the mass number of our carbon atom? = neutron= proton Obj. 4 Obj. 4

11. Isotopes: Not All Atoms are Created Equal IsotopesIsotopes are atoms of the same element that have different numbers of neutrons. –therefore they will have different mass numbers –this is the reason for the average atomic mass in the periodic table = neutron= proton Click here to compare these two atoms. These two atoms are both carbon atoms. But the atom on the left has 6 neutrons while the atom on the right has 7 neutrons. Because of this, these two atoms are said to be isotopes of one another. CLOSECLOSE Isotope: from the Greek isos, meaning “equal” and topos, meaning “place” Obj. 5 Obj. 5

12. Radioactive Isotopes Sometimes having too many neutrons can make the nucleus of an atom unstable. –Unstable nuclei decay, or break apart. –Particles (usually neutrons) and energy in the form of radiation are released. –This radiation can be used to calculate the age of an object or it can be used in medical treatments such as radiation therapy.

13. A Few Words About Electrons High energy particles Are attracted to (+)ve protons in the nucleus – keeps them close together Constant energy of motion prevents them from collapsing into nucleus Exact path of travel cannot be known An electron’s energy confines it to an energy level within the electron cloud Electrons with higher energy occupy energy levels farther from the nucleus

14. Orbitals Energy levels contain orbitals which can only hold a certain number of electrons.orbitals Energy Level # of orbitals Maximum # of electrons 112 248 3918

15. Expanding the Bohr Model Example: A carbon atom We know: From periodic tableperiodic table atomic number of carbon equals six; therefore the number of electrons equals six Why? Why? From previous chartprevious chart first energy level holds two electrons maximum second energy level holds eight electrons maximum

16. = neutron= proton= electron Expanding the Bohr Model Putting it all together: Two of carbon’s electrons will be found in the first energy level of the electron cloud. The remaining four electrons will be found in the second energy level of the electron cloud. The second energy level of a carbon atom is not full. It can still accommodate four more electrons.

17. Homework: Bohr-ing Practice Using the worksheet provided as a guide, draw Bohr models for the listed atoms. Complete the summary tables for each atom after you have drawn them. HOMEWORK!! Obj. 2 Obj. 2

18. Glossary – Part 1 mattermatter – anything that occupies space and has mass massmass – quantity of matter an object has elementelement – a substance that cannot be broken down chemically into simpler substances atomatom – simplest particle of an element that retains all of the properties of that element compound – a substance containing atoms of two or more elements that are chemically combined in fixed proportions trace element trace element – an element that makes up less than 0.01% of your body mass

19. Glossary – Part 2 organic compound organic compound – a compound that contains the element carbon orbitalsorbitals – a three-dimensional region around a nucleus that indicates a probably location of an electron isotopesisotopes – atoms of the same element that have a different number of neutrons chemical bonds chemical bonds – attractive forces that hold atoms together

20. Works Cited Campbell, Neil A., Brad Williamson, and Robin J. Heyden. Biology: Exploring Life. Upper Saddle River, NJ: Pearson Education, 2004. Emsley, John. The Elements. 3rd. Oxford: Clarendon Press, 1998. Postlethwait, John H., and Janet L. Hopson. Modern Biology. Austin, TX: Holt, Rinehart and Winston, 2006. "Radiation Therapy Career Overview." May School of Health Sciences. 2003. Mayo Foundation for Medical Education and Research. 28 Sep 2008.