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UW-Milwaukee BIOSCI 150 - Atoms

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BIO SCI 150 1st Edition Lecture 2 AtomsReductionist approach: organism to organ to cell to organelle to molecule to atom to protein, electron, neutronElement: substance that cannot be broken down further by chemical or other meansAtom: basic unit of matter which retains unique property, they are mostly made of spaceCompound: 2 or more different elements (atoms) combined in a fixed rationThe elements of importance to the biologist are:Major - carbon (C) hydrogen (H) oxygen (0) nitrogen (N)Minor - calcium (Ca) phosphorus (P) potassium (K) sulfur (S) sodium (Na)Chlorine (Cl) magnesium (Mg)Trace - various metalsAtomic StructureThe atom is composed of a nucleus containing protons and neutrons. This is surrounded byelectrons. The electron contains l/2000 the mass of the proton, and in scale, if the nucleus werethe size of a golf ball, the electron would be about 1 kilometer away.Elements are classified according to the number of particles they contain.Number of protons = atomic numberNumber of protons + neutrons = atomic weight (mass number)The total mass of an atom is given in terms of daltons (1.7 x 10-24g)Neutrons and protons have masses close to one daltonGenerally the mass number (atomic weight) is twice the atomic number, however the number of neutrons may vary. The number of electrons will equal the number of’ protons.Isotopes are forms of an element with different numbers of neutronsA stable isotope does not lose neutronsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.A radioactive isotope loses particles and energyOften isotopes behave chemically like the “normal” element, but can be identified and followed by their radioactivity, hence are very useful in biology.Protons and neutrons in the nucleus determine the mass and physical properties of the element. Electrons determine the chemical behaviorElectronsLow mass l/2000 of protonCarry negative chargePossess variable energyDetermine chemical propertiesParticipate in chemical reactionsHave no fixed location in an atomReside in the orbitals outside of the nucleus at different energy levels or shells and inDifferent orbitalsShells are involved in energy release or absorption – when electrons absorb energy, they more farther from the nucleus (higher shell), and when they release energy, they move closer to the nucleus (lower shell).Atoms want to have a filled outer (valence) shell, meaning there are 8 total electronsIf an atom gets down to 0 electrons to fill another, it becomes and ion. (cation: loosing electricity, anion: gaining electricity)Atoms can also share electrons with another atom to fill their shell, this is referred to as a covalent bond (single: 2 atoms share a pair of electrons, double: 2 atoms share 2 pairs of electrons, nonpolar: if both atoms are close in electronegativity-being desperate for more electrons- charge will be distributed equally and it will have no distinct negative or positive poll, polar: if one atom is more electronegative, but not strong enough to make an electron, the atoms will share and electron pair, the more electromagnetic number will have possession of the shared electrons and will acquire a partial charge)Orbitals determine molecular shape, describe the volume and are not definite paths. They may be arranged in different shapes (spherical of dumbbell shaped)Only 2 electrons can occupy any orbitalElectrons will occupy an empty orbital before a partially filled oneThe orbital shapes and orientations help determine molecular shapeFilled or empty orbitals determine reactivity of atomsOrbitals and Energy Levels (Shells)First ShellClosest to nucleusLowest energyHolds two electronsOne spherical orbital 1sSecond ShellFarther from nucleusHigher energyHolds 8 electronsOne spherical orbital 2sThree dumbbell-shaped orbitals 2p at right angles to each otherAtoms want to fill the outer shell C, N, O need 4, 3, or 2 electronsHydrogen bondThe hydrogen atom of one polar covalent molecule is attracted to the electronegative atom of another polar covalent moleculeHydrogen bonds are essential to many biological structuresThe bonds are; weak individually, easy to form and break, directional, and limited to fixed distancesVan der Waals InteractionsWeak attractions between molecules due to shifting electron distributionsForces allow molecules to “stick together”Work only over short distances, so molecular surfaces must “fit” togetherChemical ReactionsCovalent bonds are made and broken to form new molecules.Energy is required to break bonds, and released when they are formed.Some reactions go both ways and equilibrium is established, where they can infinitely go back and forth, since the cells are trying to push them in the direction they


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