CHAPTER 2 Flashcards
define: atoms, electrons, protons, and neutrons
-atoms: smallest unit of matter
-electrons: negligible mass; negative charge
-protons: have mass; positive charge
-neutrons: have mass; no charge
mass of one proton/neutron?
1 dalton or 1.7 x10^-24 grams
define: element, atomic number. mass number
-element: fundamental substance containing only one kind of atom
-atomic number: number of protons in an element
-mass number: protons + neutrons
define isotopes. give examples
-isotopes: forms of an element with different numbers of neutrons, and thus different mass numbers
-EX: carbon isotops; C12, C13, C14
define: radioistopes, radioactive decay, molecule
-radioisotpes: give off energy in the form of alpha, beta, and gamma radiation from the nucleus (radioactive decay). the atom is transformed, sometimes to a different element
-radioisotopes can be incorporated into molecules to act as a tag or ;Abe;
-molecule: a stable association of atoms
what determines how an element will combine with other atoms? define orbital. define electron shells
-the number of electrons in an atom determines how it will combine with other atoms
-orbital: region where an electron is found at least 90% of the time
-electron shell: The region surrounding the atomic nucleus at a fixed energy level in which electrons orbit.
what does the first shell, second shell, and additional shell hold?
-first shell: 1 orbital; holds 2 electrons
-second shell: 4 orbitals; hold 8 electrons
-additional shells: 4 orbitals; hold 8 electrons
relationship between shell distance from the nucleus and energy level of electrons in that shell?
the farther a shell is from the nucleus, the higher the energy level of electrons in that shell
define valence shell. what makes an atom reactive or stable?
-valence shell: The outermost energy shell of an atom, containing the valence electrons involved in chemical reactivity.
-if the outermost shell is full, the atom is stable; it wont react with other atoms
-having unpaired electrons in their outermost shell will make an atom reactive
how do reactive atoms become stable? define octet rule
-reactive atoms can share, lose, or gain an electron; which results in a bond together to form molecules
-octet rule: tendency of atoms to form stable molecules resulting in full valence shells
define: chemical bond, covalent bond
-chemical bond: attractive force that links atoms together to form molecules
-covalent bonds: (very strong) atoms share one or more pairs of electrons so that the outer shells are filled; a lot of energy required to break them
define: compound, molecular weight
-compound: pure substance made up of two or more different elements bonded together in a fixed ratio
-molecular weight of a compound = the some of atomic eights of all atoms in the molecule
what give molecules their shape? what does molecule shape change do?
-length, angle, and direction of bonds between any two elements are always the same; this orientation gives molecules their shapes, which contributes to their biological functions
-molecule shape can change as atoms rotate around a covalent bond
define electronegativity
-attractive force that an atomic nucleus exerts on electrons
-depends on number of protons and distance between the nucleus and electrons
define: polar covalent bond, non polar covalent bond
-non polar covalent bond: electrons are shared equally (atoms have similar electronegativity)
polar covalent bond: one atom has greater electronegativity, so electrons are drawn more to that nucleus
define ionic bonds
-when one atom is much more electronegative than the other, a complete transfer of electrons may occur
-this results in two ions with full outer shells
-formed by electrical attrition of positive and negative ions
define: ions, cations, anions, and complex ions
-ions: electrically charged particles formed when atoms lose or gain one or more electrons
-cations: positive
-anions: negative
-complex ion: group of covalently bonded atoms that carry a charge
define hydrogen bonds
-attraction between the δ– end of one molecule and the e δ+ hydrogen end of another molecule
-these bonds are weaker than ionic and covalent bonds
-many hydrogen bonds in a large molecule can be strong and play important role in the structure of DNA and proteins
define hydrophilic and hydrophobic
-hydrophilic: polar molecules that form hydrogen bonds with water (water loving)
-hydrophobic: non polar molecules, such as hydrocarbons (water hating)
what is Van Der Waals forces?
-attraction between non-polar molecules that are close together
-individual interactions are brief and weak, but can be substantial when summed over a large molecule
-when hydrophobic regions of molecules such as an enzyme and a substrate come together
what is a oxidation-reduction reaction?
-electrons are transferred between two molecules
-the electron acceptor gains electrons and become reduced
-the electron donor loses electrons becomes oxidized
-EX: combustion reaction
when do chemical reactions occur?
-occur when atoms collide with enough energy to combine or change their bonding partner
define energy
-capacity to do work or the capacity for change
-energy usually changes form during chemical reactions
what causes water’s unusual properties? what are water’s unusual properties?
-since water is polar it has many unusual properties
-ice floats; the space between molecules as ice makes it less dense than water
-water has high specific heat; (amount of energy needed to raise temperature of 1 gram of a substance by 1 degree C)
-ice requires a lot of energy to melt, to break the hydrogen bonds; when water freezes, a lot of energy is released to the environment
-water has high heat of evaporation; a lot of heat energy is required to change water from the liquid to gaseous stare; the heat must be absorbed from the environment in contact with the water and results in cooling
-cohesion: hydrogen bonds between water molecules cause them to stick together; helps water move through plants; results in surface tension
-adhesion:attraction of water molecules together molecules of a different type
-solution:substance dissolved in a liquid; water is a great solvent to polar atoms
define acids & bases. give examples of weak and strong
-acids: release hydrogen ions
(H+) in water
-weak acids: not all the acid molecules dissociate into ions (EX: CH3COOH acetic acid)
-strong acid: completly dissociate (HCL)
-bases: accept H+ ions
-strong base: NaOH
-weak bases: bicarbonate ion(HCO3-), ammonia (NH3). and compounds with amino groups (NH2)
what can happen with acid-base reactions?
-acid base reactions may be reversible
-ionization of strong acids and bases is irreversible
-ionization of weka acids and bases is somewhat reversible
define pH. what does low, high, neutral pH mean?
-pH: negative log of the molar concentration of free H+ ions in the solution
-lower pH numbers (less than 7) means higher H+ concentration; greater acidity
-higher pH means its basic (more than 7)
-neutral pH means its neutral duh (equal 7)
define: buffer, law of mass action
-buffer: a weak acid and its corresponding base; buffers help maintain constant pH
-buffers illustrate the law of mass action: addition of reactant on one side of a reversible system drives the system in the direction that uses up that compound
