BSC2010 Test 1 Review Bates chemical reactions Element A substance that cannot be broken down to other substances by o There are 92 elements that occur naturally o 20 25 are essential elements that an organism needs to life Humans need 25 elements plants only need 17 o Oxygen carbon hydrogen and nitrogen make up 96 of living matter o Calcium phosphorus potassium sulfur and few other elements make up the remaining 4 o Trace elements required by an organism in only minute quantities Compound A substance consisting of two or more different elements Atom the smallest unit of an element retaining its properties combined in a fixed ratio o Table salt NaCl 1 1 ratio o Subatomic particles Nucleus Neutrons neutrally charged Protons positively charged A neutron and proton have a mass of 1 amu or 1 7 x10 27 gram or 1 dalton Electrons Negatively charged Mass 1 2000 of a proton Atomic number The number of protons in an atom s nucleus Mass number The sum of protons and neutrons in the nucleus o Number of neutrons mass number atomic number Number of protons equals the number of electrons in an uncharged atom Atomic mass Total mass of an atom Molecular weight the sum of the atomic weights of atoms in a molecule o H2O MW 1 1 16 18 Isotope Atoms of that have the same number of protons but a different number of neutrons o Behave identically in chemical reactions but may have different Radioactive isotope An isotope where the nucleus decays spontaneously physical properties giving off energy o When it leads to a change in the number of protons it transforms the atom to an atom of a different element Only electrons are directly involved in chemical reactions Potential energy The energy that matter possesses because of its location or structure potential energy o The more distant an electron is from the nucleus the greater its o An electrons potential energy is determined by its energy level and average distance from the nucleus o Electrons are found in electron shells The first shell is closest to the nucleus and electrons in this shell have the lowest potential energy The second shell has more energy than the first and the third has even more energy When an electron absorbs energy it moves to a higher shell When it loses energy it falls back to a shell closer to the nucleus the lost energy is released as heat Orbital The three dimensional space where an electron is found 90 of the time o An orbital is a component of an electron shell The first shell has one spherical s orbital called 1s and can hold only 2 electrons The second shell has 4 orbitals one s orbital called 2s and 3 dumbbell shaped orbitals called 2p It can hold up to a maximum of 8 electrons No more than 2 electrons can occupy a single orbital Valence shell The outermost electron shell Valence electrons the outer electrons Atoms seek to gain or lost electrons until their valence shell is filled 8 paired electrons Valency The bonding capacity of an atom based on the number of unpaired electrons required to complete the atom s valence shell o Monovalent 1 electron Na K Cl o Divalent 2 electrons Ca Mg O o Trivalent 3 electrons o Tetravalent 4 electrons o Pentavalent 5 electrons Covalent bond The sharing of a pair of valence electrons by 2 atoms o Single bond a pair of shared electrons o Double bond Sharing two pairs of valence electrons o Covalent bonds are the strongest o Non polar covalent bond the electrons are shared equally because the two atoms have the same electronegativity C C and C H covalent bonds are non polar o Polar covalent bond When an atom is bonded to a more electronegative atom the electrons are not shared equally H2O is a polar covalent bond The electrons spend more time near the oxygen nucleus because the oxygen has a slight negative charge while the hydrogens have a slight positive charge O H and N H are polar covalent bonds The oxygen and nitrogen have partially negative charges Oxygen is one of the most electronegative elements Molecule Two or more atoms held together by covalent bonds Ionic bonds Electrical attraction between 2 atoms one that has gained an electron and one that has lost one o The more electronegative atom strips an electron away from its partner These opposite charges means the cations and anions attract each other which forms a bond o NaCl The lone electron sodium is transferred to the chlorine atom and both atoms end up with complete valence shells o Ionic compounds salts Compounds formed by ionic bonds o Ionic bonds are the 2nd strongest bonds Hydrogen bonds The attraction between compounds held together by polar covalent bonds o The hydrogen of one water molecule will form a hydrogen bond with the oxygen of another water molecule o Hydrogen bonds are weak bonds Van der Waals interactions Weak attraction of uncharged atoms and occur only when atoms and molecules are very close together Molecular formula Identifies the elements and the number of given atoms in o Weakest bond a molecule o H2O CH4 o H O H Structural formulas Shows the number and arrangement of covalent bonds in a compound Mole Amount of a compound equal to its molecular weight in grams o H2O 1 mole 18 g o One mole of a compound contains 6 x 1023 atoms Molarity The measure of the moles of a solute dissolved in a liter of a solution o 1M 1 mole 1L o 1mM 10 3 M 0 001 moles L Solutions Most biological compounds are present as a homogenous suspension in water o Solvent The dissolving medium water o Solute The dissolved substance Metric system units o 1 Kg 1000g o 1000mg 1 g o 1000 g 1mg o 1L 1000mL o 1mL 1000 L o Micro 10 6 o Milli 10 3 Chemical reactions The making and breaking of chemical bonds o Reactants The starting materials o Products The converted starting materials Water o Chemical equilibrium The point at which the reactions offset one another Reactions are still going on but with no net change on the concentrations of reactants and products The forward and reverse reactions occur at the same rate and the relative concentrations of products and reactants stop changing Equilibrium constant Ratio of concentrations of products and reactants at equilibrium Keq product C product D Reactant A Reactant B Irreversible reactions Reaction goes fully to the right Keq 1 o Cohesive Hydrogen bonds hold the water molecules together Allows the transport of water o Adhesion The clinging of one substance to another Allows water to stick to the molecules of well walls which counters the downward pull of gravity o Surface tension A measure of
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