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Chem 152 exam 2
Terms in this set (85)
Democritus' atomic theory
atoms were indivisible and indestructible
Continuous matter theory
matter can be subdivided infinitely without reaching ultimate particles
particulate (atomic) theory
subdividing matter repeatedly eventually reaches a smallest particle that cannot be further subdivided, the atom
Dalton's atomic theory (*)
1. all matter is made up of indivisible atoms
2. every atom of the same element has the same properties, especially its atomic weight.
3. atoms of elements combine in specific whole number ratios to make a given compound
Which laws support Dalton's atomic theory?
the law of conservation of mass/ the law of definite composition
law of definite composition
compounds are always composed of the same elements in the same proportion
law of conservation of mass
total mass of reactants must equal the mass of the products
law of multiple proportions
two or more elements can combine in different proportions by mass to form different compounds
revisions to Dalton's theory
1. atoms are not indivisible, atoms are composed of subatomic particles
2. not all atoms of the same element have an identical mass (isotopes)
3. nuclear reactions decompose atoms.
atomic mass (atomic weight)
mass of one atom in amu's; may be found in tables
formula mass (formula weight)
mass obtained by adding up atomic masses in chemical formula
quantity of a substance (atoms, molecules, etc) that contains Avogadro's number of particles. (1 mole of atoms/molecule/electrons etc.= 6.022x10^23 atoms/molecules/electrons etc.)
a conversion factor that is used for conversions between number of moles and number of particles. (6.022x10^23)
numerically the same as atomic mass, but in g/mole, not amu's.
molar mass as a conversion factor
used for converting between mass and number of moles.
molecular/formula mass (molecular/formula weight)
mass of 1 molecule in amu's; found by adding up atomic weights of all the atoms represented in the chemical formula.
chemical formula in which subscripts represent smallest whole number ratio of atoms or ions in a substance; also represent the smallest whole number ratio of moles or atoms or ions in the substance.
why is the empirical formula important?
even though compounds with the same empirical formula have the same percent composition, they have very different chemical and physical properties.
actual chemical formula of a compound. represents the total number of atoms in one formula unit of the compound; represent exact number of moles of atoms of each element in one mole of entire substance.
protons, neutrons, electrons
Positively charged particles ~1 amu
neutral particles that do not have an electrical charge 1 amu
negatively charged particles. almost no mass (.0005)
Rutherford's Alpha Scattering experiment
Involved the scattering of positively charged alpha particles through a 3-4 atom thick gold sheet. If the chocolate chip cookie model is correct, then all the alpha particles should pass through. Instead, 1% deflected and .01% bounced back. His experiment proved the existence of a positive, dense nucleus. (nuclear model of the atom)
Plum Pudding model
Negative and positive charges distributed evenly throughout the atom. suggested by JJ Thompson.
nuclear model for the atom
atom has a small centrally located nucleus that contains all the positive charge and almost all the mass of the atom. the negatively charged electrons are scattered outside the nucleus. the atom is mostly empty space.
Atomic number, Z
number of protons in atom or ion. each element has a unique atomic number which identifies the element.
Atoms with the same number of protons but different numbers of neutrons, thus resulting in different mass numbers.
mass number, A
number of protons + number of neutrons (always an integer)
Mass number on top. Atomic number/number of protons on bottom. charge to the upper right.
An atom or group of atoms that has a positive or negative charge, meaning the number of electrons and number of protons are different.
electrons are lost from atoms (positively charged)
electrons are gained from atoms (negatively charged)
atomic mass (weight)
weighted average of masses of all the naturally- occurring isotopes of an element.
Bohr model of atom
1. electron revolves around nucleus in circular path or orbit (stationary state or energy level). energy is greater the further the orbit is from nucleus
2. as long as electron remains in same energy level, it does not change energy.
3. electron can change levels. if it gains energy it can move to a higher level. if it loses or emits energy it may go to a lower level.
Limitation of Bohr model
it did not work well for atoms having more than one electron.
Arnold Sommerfield's modification of the bohr model of the atom
1. the allowed orbits could be elliptical
2. required two quantum numbers: n for the size of the orbit, and l for the shape.
limitation of Arnold Sommerfield modification
it assumed a certain definiteness in the motion of the electron around the nucleus.
what did Louis de Broglie suggest?
that matter might have a wavelength and that wavelength is inversely related to mass.
since electron is so small, wavelength is significant
electron wavelength significance and Bohr model
because of the wavelength properties of an electron, its motion could not be known with the definiteness implied by the Bohr model.
Heisenberg Uncertainty Principle
it is not possible to know precisely both the location and the momentum of the electron. the more precisely the location is known, the less precisely the momentum is known.
Quantum (wave) mechanical model.
rather that following a precise orbit, the electron occupied an orbital.
a volume of space in which there is a high probability of finding the electron.
principal quantum number, angular momentum quantum number, and magnetic quantum number
principal quantum number
n; energy level. associated with the average distance of electron from the nucleus. the higher the energy level, the further away from the nucleus.
angular momentum quantum number
l; sublevel. associated with sublevel containing orbitals of particular shape. the number of sub levels in an energy level is the same as the principal quantum number.
1 orbital, 2 electrons
dumbbell shaped (2 lobes)
3 orbitals, 6 electrons
clover shaped (4 lobes)
5 orbitals, 10 electrons
7 orbitals, 14 electrons
pauli exclusion principle
there can never be more than two electrons in the same orbital
the lowest energy state of an atom or other particle which occurs when an atom or ion occupies the lowest available orbital.
when electrons occupy higher energy orbitals while there are lower energy vacancies
electrons go into separate orbitals within the same sublevel until each orbital is half filled (contains 1 electron) before beginning to pair up in the same orbital.
the electron configuration of an element is same as electron configuration of the previous element plus one additional electron.
An electron in the highest occupied energy level or shell of an atom. they are primarily responsible for the behavior of elements.
Which blocks are main group elements?
s and p blocks.
which blocks are transition elements?
d and f block
what does group number tell you about main group elements?
number of valence electrons in a neutral atom. this also tells you that elements in that column have similar behaviors.
elements other than H in group 1a
alkaline earth metals
elements in group 2a
elements in group 7a
elements in group 8a
modern periodic law
the chemical and physical properties of the elements are periodic functions of their atomic numbers.
What 5 periodic properties can we extrapolate from the period table.
1. atomic size (atomic radius)
2. ionization energy
3. electron affinity
4. metallic character
5. nonmetallic character
Atomic size (atomic radius)
generally increases down a group due to the increasing number of occupied energy levels, causing the energy level to be further from the nucleus.
generally decreases toward the right across periods because increasing nuclear charge draws the energy levels closer to the nucleus.
the amount of energy needed to remove one valence electron from a neutral atom to form a +1 ion.
decreases down a group because shielding and distance from the nucleus makes it easier to lose electron.
increases toward the right across periods because increasing nuclear charge makes it hard to lose electrons.
the energy change when an electron is added to a neutral atom to form a -1 ion. usually negative.
the more negative the electron affinity, the greater tendency to gain an electron.
related to the tendency of the atom to lose one or more valence electrons.
generally increases down group with decreasing ionization energy making it easier to lose electrons.
decreases to right across periods with increasing ionization energy making it harder to lose electrons.
related to the tendency of the atom to gain one or more electrons in the valence energy level.
generally decreases down a group due to distance of valence electrons from nucleus which increases shielding making it harder to gain electrons.
increases across periods because increasing nuclear charge makes it easier to gain electrons.
(lewis) octet rule
elements try to attain the same electron configuration as one of the noble gases. usually this means getting 8 valence electrons. they do this by gaining or losing electrons forming negative or positive ions.
metals vs. nonmetals and gaining or losing electrons
metals tend to lose electrons to form positive ions, and nonmetals tend to gain electrons to form negative ions.
electrostatic attraction between positive and negative ions to make a compound.
electronegativity difference greater than 1.6
normally a metal and a nonmetal.
compound formed when ions are held together by ionic bonds.
A chemical bond that involves sharing a pair of electrons between atoms in a molecule
normally two nonmetals.
single covalent bond
one pair of electrons shared between two atoms
double covalent bond
two pairs of electrons shared between two atoms.
triple covalent bond
three pairs of electrons shared between two atoms.
tendency of an atom to attract electrons toward itself
tends to increase toward the right across period due to increase nuclear charge.
tends to decrease down a group due to increasing distance of valence electrons
nonpolar covalent bond
equal sharing of electrons
electronegativity difference less than .4
or if adjacent (side by side or one above the other) on the periodic table.
polar covalent bond
unequal sharing of electrons. electronegativity difference between .5-1.6
or if they are not adjacent on periodic table.
properties of ionic substances
high melting point, solid at room temperature, insoluble in nonpolar solvents.
bad conductors of heat and electricity in a solid state but excellent conductors of electricity in an aqueous solution
properties of nonpolar substances
low melting point. low boiling point. soluble in non poplar solvents. insoluble in polar solvents. bad conductors of heat and electricity in any state.
properties of polar substances
intermediate melting and boiling points. soluble in polar solvents. insoluble in nonpolar solvents. aqueous solutions may be strong or weak conductors of electricity.
pure form generally non conducting but there are some exceptions.
properties of metallic substances
excellent conductors of heat and electricity in solid state, most are solid and room temperature (except Hg). consist of positively charged cores in sea of free flowing valence electrons.
Recommended textbook explanations
Exploring Chemical Analysis
Daniel C. Harris
Introductory Chemistry Essentials
Nivaldo J. Tro
Modern Chemistry: Study Guide
Rinehart, Winston and Holt
Principles of General Chemistry (International edition)
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