Lecture 3 on Biology for Health Sciences

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BIOL - Biology
BIOL 105
Gregory Zagursky

Atoms and Molecules Everything an organism is and does depends on chemistry Chemistry is in turn dependent on the arrangement of atoms and molecules Ultimately the atoms function by the rules of physics Life requires about 25 chemical elements A chemical element is a substance that cannot be broken down to other substances by ordinary chemical means  About 25 elements are needed to sustain/be used in life Basic chemistry Chemical elements  Carbon-C  Hydrogen-H  Nitrogen-N  Oxygen-O  Phosphorous-P  Sulfur-S  “CHNOPS” Atoms consist of protons, neutrons and electrons The smallest part of an element is an atom Different elements have different types of atoms  An atom is made up of protons and neutrons located in a central nucleus  The nucleus is surrounded by electrons Each atom is held together by attractions between the positively charged protons and negatively charged electrons  Neutrons remain neutral Atoms of each element are distinguished by a specific number of protons  The number of neutrons may vary  Variant forms of an element are called isotopes  Some isotopes are radioactive Radioactive isotopes can help or harm us Radioactive tracers are frequently used in medical diagnosis Sophisticated imaging instruments are used to detect them  An imaging instrument that uses positron emission tomography (PET) detects the location of injected radioactive materials  PET is useful for diagnosing heart disorders and cancer and in brain research Atoms and Molecules Elements can combine to form compounds Chemical elements combine in fixed ratios to form compounds  Ex. Sodium+ chloride = sodium chloride Ionic Bonds are attractions between ions of opposite charge When atoms gain or lose electrons, charged atoms called ions are created An electrical attraction between ions with opposite charges result in an ionic bond Covalent Bonds, the sharing of electrons, join atoms into molecules Some atoms share electrons with other atoms, forming covalent bonds  Atoms joined together by covalent bonds form molecules  Covalent bonds in molecules can be represented in many ways Chemical Bonds Covalent  Atoms in a covalently bonded molecule may share electrons equally, creating a nonpolar molecule  If electrons are shared unequally, a
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