Bio 111 Ch 2: The Chemical Context of Life PDF

Ch 2. The Chemical Context of Life Julia E. Porado MS CT(ASCP) Matter  Anything that takes up space and has mass  Everything is composed of matter Chemical elements in pure form, and/or in combinations (“compounds”) Elements v. Compounds  Matter is made u...

Ch 2. The Chemical Context of Life Julia E. Porado MS CT(ASCP) Matter  Anything that takes up space and has mass  Everything is composed of matter Chemical elements in pure form, and/or in combinations (“compounds”) Elements v. Compounds  Matter is made up of elements A substance that cannot be broken down to other substances by chemical reactions  Ex: Carbon, hydrogen, oxygen, sodium, etc  92 elements occur in nature  Compound  Consists of two or more different elements combined in a fixed ratio  Ex: Sodium Chloride (NaCl). Na and Cl in a 1:1 ratio; water (H2O) H and O in a 2:1 ratio Structure of an atom The Elements of Life (p.29)  Essential elements  Necessary for life  Similar between organisms; some variation  Humans require 25 elements to survive  Plants require 17 elements to survive  96% of living matter made up of 4 4% of living matter mostly made up by elements Calcium (Ca) Phosphorous (P)  Oxygen (O) Potassium (K)  Hydrogen (H) Safer (S)  Nitrogen (N)  Carbon ( C ) Trace elements  Required by an organism in minimal quantities  Some, such as Iron (Fe), are required in all forms of life  Others are only required by certain species  Some naturally occurring elements can be toxic to organisms  Ex: arsenic –Linked to disease; can be lethal  An element’s properties depend on the structure of it’s atoms  Atom- smallest unit of matter that still retains the properties of an element  Subatomic particles-  Neutrons- no charge  Protons- positive charge (+)  Electrons- negative charge (-) Atomic nucleus- protons and neutrons packed together at the center of an atom; protons give the nucleus a positive charge Electron “cloud” around the nucleus is negatively charged. Opposite charges attract each other and hold the atom together Atomic number and atomic mass  Atomic number- the number of protons unique to that element  Mass number-total number of neutrons and protons within the nucleus of an atom  Atomic mass- close to the mass number, measured in daltons  Dalton-atomic mass unit, used to quantify subatomic particles Neutrons and protons each have a mass very close to 1 dalton Isotope  Some atoms have more neutrons than other atoms of the same element  Isotope Has greater mass  in nature, an element may occur as a mixture of its isotopes  Radioactive isotope- an isotope in which the nucleus decays spontaneously, giving off particles and energy  When the radioactive decay of an atom leads to a change in the number of protons—>transforms the atom to an atom of a different element Radioactive tracer  Radioactive isotopes are often used as diagnostic tools in medicine  Can be ingested/injected into human body, targeting specific areas  Utilizes physiology to highlight problem areas Used to image thyroid disease Energy levels of electrons  An atom’s electrons vary in the amount of energy they possess  Energy- the capacity to cause change By doing work  Potential energy- the energy that matter possesses because of its location or structure Ex:water in a reservoir on a hill—>the water has potential energy due to its altitude  The electrons of an atom have potential energy due to their distance from the nucleus  The electrons’ (-) attraction to the protons (+) (nucleus)  Energy levels of electrons (continued)  It takes work to move an electron away from the nucleus  The more distant an electron is from the nucleus, the greater its potential energy  An electron’s potential energy depends on its energy level  Electron shells The further a shell is from the nucleus, the higher its energy level  An electron can move from one shell to the other by absorbing or losing energy Absorbing energy—> moves to a shell farther from the nucleus Losing energy—> “falls back” to a shell closer to the nucleus Electron distribution and chemical properties (p.34)  The chemical behavior of an atom is determined by the distribution of electrons in the atom’s shells  Valence electrons- occupy the outermost shell (“valence shell”)  An atom with a completed valence shell is nonreactive- inert  Ex: noble gasses  Will not readily react with other atoms Electron orbitals (p. 35)  The 3d space an electron is found 90% of the time.  Not a circle like the previous diagrams  Each electron shell contains electrons of a particular energy level, distributed among a specific number of orbitals of distinctive shapes and orientations  Each orbital has a maximum of 2 electrons Chemical bonds  The formation and function of molecules and ionic compounds depend on chemical bonding between atoms  Atoms with incomplete valance shells can interact with other atoms in such a way that each partner atom shares a valence shell  They share or transfer electrons Atoms held together by electron interactions- chemical bonds Covalent bond  The sharing of a pair of valence electrons by two atoms  Single bond- one pair of electrons is shared  Double bond- two pairs of electrons are shared Valence  Each atom has a bonding capacity corresponding to the number of covalent bonds an atom can form  Valence  Ex on board: carbon, oxygen Electronegativity  Atoms in a molecule attract shared bonding electrons to varying degrees, depending on the element  Electronegativity- the attraction of a particular atom for the electrons of a covalent bond  The higher the electronegativity of an atom—> stronger it pulls shared electrons to itself  Ina covalent bond between atoms of the same element, the electrons are shared equally because both atoms have the same electronegativity  “nonpolar covalent bond”  When an atom is bonded to a more electronegative atom, the electrons of the bond re not shared equally  “polar covalent bond” Polar Covalent Bond Ionic bonds  In some cases, two atoms are so unequal in their attraction for valence electrons that the more electronegative atom strips an electron completely away from its partner  Resulting in two oppositely charged atoms- ions  Cation- positively charged  Anion- negatively charged  Due to their opposite charges, cations and anions attract each other – ionic bond  Ionic compounds (“salts”)- compounds formed by ionic bonds  Weak chemical interactions  Hydrogen bond-  when a hydrogen atom is covalently bonded to an electronegative atom, the hydrogen atom has partial positive charge which allows it to be attracted to a different electronegative atom with a partial negative barge nearby  Noncovalent  Van dear Waals Interactions-  The ever changing positively and negatively charged regions of a molecule based on the movement of electrons and electronegative attractions  Attraction between atoms due to these charged regions interacting when atoms are close by  Weakest chemical interaction Hydrogen bond Chemical reactions make or break chemical bonds (p.40-41)  Chemical reactions- the forming or breaking of chemical bonds, leading to changes in the composition of matter  Reactants-starting materials  Products- resulting materials  Chemical equilibrium- the point at which two reactions offset each other-balance END