Atoms and Molecules Nestor T. Hilvano, M.D., M.P.H. (Images Copyright Discover Biology, 5th ed., Singh-Cundy and Cain, Textbook, 2012.)

Learning Objectives Definition of terms: matter, element, compound, atom, molecule, isotopes, ionic bond, covalent bond, and H bond. Describe the structure of an atoms. Discuss the beneficial and harmful effects of isotopes in man. List 4 major elements of the human body. Differentiate the types of chemical bonds. What is H bond and give it’s importance?

7 major minerals/electrolytes: Ca++, P, K+, Na+, Cl-, Mg++, S ___ What is everything around you that occupies space and has mass (composed of elements)? ___ What substances cannot be broken down into simpler (other) substances? 96% of the human body is composed of 4 elements (COHN) 7 major minerals/electrolytes: Ca++, P, K+, Na+, Cl-, Mg++, S 16 trace elements: Fe, I Elements b. Molecules c. Matter d. Compounds

Atoms Smallest unit of matter Subatomic particles Protons -positive charge (in the nucleus of an atom) neutrons -no charge (in the nucleus) electrons -negative charge (orbit in shells around the nucleus) Atomic number- tells us the no. of p+ and also the no. of e- Atomic mass (weight)- equals the no. of p+ and no. of nº Number of nº = atomic weight – atomic number i.e. C (atomic no. 6, atomic mass 12) O (atomic no. 8, atomic mass 16) H (atomic no. 1, atomic mass 1) Na (atomic no. 11, atomic mass 23) Cl (atomic no. 17, atomic mass 35)

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2 He 4 Helium Nucleus 2e Electron cloud 2 Protons Mass number  4 Figure 2.3A Helium 2 He 4 Nucleus Electron cloud 2 Protons Neutrons Electrons Mass number  4 2e Figure 2.3A Two models of a helium atom 6

Isotopes Atoms of the same element but have different numbers of neutron - isotopes of Carbon (C-12, C-13, C-14) Radioactive (unstable) isotopes- nucleus decays giving off particles and energy (ex. C-14, N-16) Harmful effects – cause disease, birth defects, death Uses or beneficial effects – markers or tracers, diagnostic procedures, treatment

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Figure 5.3 Radioisotopes Are Useful in Medical Imaging (a) The thyroid gland, located in the neck, helps regulate metabolism. The element iodine accumulates in the gland and is necessary for normal thyroid function. (b) This image is a visualization of the thyroid gland in a patient with goiter, an enlargement of the thyroid gland, often caused by iodine deficiency. Small amounts of radioactive iodine were given to the patient, and the accumulated radioisotope was visualized with a gamma-ray scan.

Chemical Bonds Electrons- part of an atom that interact; arranged in shells - innermost shell = full w/ only 2e - outermost shell = up to 8e Atoms whose outermost shell are not full will participate in a chemical bonds Exercises: Give the no. of electron shells and no. of electrons in the outermost shell (valence electrons) of the ff.: Na (atomic no. 11), H (atomic no. 1), C (atomic no. 6), N (atomic no. 7), O (atomic no. 8), Cl (atomic no. 17); and Mg (atomic no. 12)

Chemical Bonds # of shells determined by # of protons (electrons) Figure 2.5_1 Chemical Bonds Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminum Silicon Phosphorus Sulfur Chlorine Argon Figure 2.5_1 The electron distribution diagrams of the first 18 elements in the periodic table # of shells determined by # of protons (electrons) atoms want the outermost shell to be filled =STABILITY 11

Ionic Bonds Attraction of ions of opposite charges, Gaining or losing of electrons Ions are atoms with an electrical charge resulting from a gain of e-, anion; or loss of e-, cation. Ionic bond- ex. NaCl Weak bond- salt dissolves in water

Na Sodium atom Cl Chlorine atom Na Sodium ion Cl Chloride ion Figure 2.7A_s2 Transfer of electron Na Sodium atom Cl Chlorine atom Na Sodium ion Cl Chloride ion Figure 2.7A_s2 Formation of an ionic bond, producing sodium chloride (step 2) Sodium chloride (NaCl) Na (atomic no. 11, atomic mass 23) Cl (atomic no. 17, atomic mass 35) 13

Covalent bonds Molecule – 2 or more atoms held together (ex: O2) Compound- 2 or more types of atoms (different elements) joined together (ex: CO2) Covalent bonds – 2 atoms share one or more pairs of outer shell electrons; very strong bond a) Nonpolar covalent bond -electrons are shared equally between the atoms (H2, O2, CH4). b) polar covalent bond -unequal sharing of electrons (H2O).

Weak Chemical Bonds Hydrogen (H) bonds- weak bonds as in H20 molecules Importance: occur in other biological compounds like proteins and DNA, form bridges between molecules http://www.elmhurst.edu/~chm/vchembook/162othermolecules.html http://www.dna-sequencing-service.com/dna-sequencing/dna-hydrogen-bonds-2/

Homework (Self Review) Define terms: matter, atom, element, molecule, compound, ionic bond, covalent bond, polar covalent bond, nonpolar covalent bond, ion, anion, cation, and isotopes. Name and describe the 3 subatomic particles of an atom. List the 4 major elements of the human body. Discuss how isotopes cause harmful effects to human. Oxygen has atomic number of 8. What is the number of valence (outermost) electrons?