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CHEM-C 117: EXAM 1
law of conservation of energy (first law of thermodynamics)
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states that energy can be neither created nor destroyed--the total energy of the universe is constant
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Hess's Law
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if two or more chemical equations can be combined to give another equation, then enthalpy change for that equation will be the sum of the enthalpy changes for the equations that were combined.
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thermodynamics
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the science of heat, work, and the transformations of each into into the other
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Cal |
kilocalorie
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cal
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calorie |
1 Cal(kilocal)=
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4184 Joules
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1 cal=
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4.184 joules
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open system
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exchange mass and energy
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closed system
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exchange energy--not mass
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isolated system
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does not exchange energy or mass
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heat capacity
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accounts for transfer of energy between sameples of matter as a result of temperature differences
- quantity of energy required to increase the temp of an OBJECT by one degree
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energy transfers
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accompant physical and chemical changes, even though there may be no change in temperature
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work |
transfering energy to an object
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total internal energy
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sum of individual energies, depends on temperature, type of particles and NUMBER of particles in sample
ex: hot tub has more energy than boiling water
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law of conservation of energy equation
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delta E= q (quantitiy of energy) + w (work on system)
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specific heat capacity
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amount of energy needed to raise 1 g of sample by 1 degree celcius
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specific heat capacity equation
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c= q/(m*delta T)
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molar heat capacity
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quantity of energy that must be transferred to increase the temp of one mole by one degree celcius
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liquid to gas
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endothermic becuase energy must be transfered in to maintain constant temp
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gas to liquid
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opposite of boiling-- condensation
exothermic
energy must be transfered out to maintain temp
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burn from steam of water worse? why?
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steam becuase of condensation.. steam hurts skin a lot more becuase there is a heat transfer due to condensation as well as the differece in temp between the water and your skin
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work |
when a force moves something through some distance
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enthalpy change
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amount of thermal energy transferred into a system at constant pressure
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phase change
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temperature remains constant, but energy must be continually transfered into (melting boiling) or out of the system (condensing, freezing)
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enthalpy of vaporization
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amount of energy needed to be transfered at constant pressure to convert liquid to vapor (gas)
LARGER THAN ENTHALPY OF FUSION
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state functions
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properties that define a state but do not rely on the path taken to arrive at that state.
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if there is one mole of H2O(l) --> H20 (g) what is delta H?
if there are two moles of H20(l)-->H2O(g) what is delta H?
if there is one mole of H20 (g) --> H20(l)?
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44 kJ
88 kJ
-44 kJ
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chemical reactions involve much larger...
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energy transfers
**significant temp change is a sign of chemical reaction
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standard molar enthalpy formation (delta H sub f)
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standard enthalpy change for formation of one mole of compound from its elements in their standard states
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chemical fuel
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any substance that will react exothermically with atmospheric oxygen
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if bonds formed are stronger than bonds broken
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exothermic reaction
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hydrogen as fuel
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not good becuase it is rare naturally as an element, it is almost always in a compound so it it expensive to manufacture. Its also hard to store because it is not easily condensed into water for denser storage
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cellulose formula
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CH2O
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fuel value
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amount of energy released when 1g of fuel is burned to form carbon dioxide and water
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energy density
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amount of energy released per unit volume of fuel
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generation and distribution of electricity is only ____ efficient
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33%
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food consists of mainly
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carbs, proteins, and fats
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glucose formula
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C6 H12 O6
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carbs |
metabolize quickly. powers muscles, transmits nerve impulses, repair tissue, maintains body temp--all extra stored in fats
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fats
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not water soluble
stores more than twice the energy as proteins of same mass
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protein |
release energy. metabolic rate same as carbs
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ethanol
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contributes calories becuase it can be metabolized exothermically
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Basal metabolic rate (BMR)
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minimum energy intake required to maintain a body that is awake and at rest, excluding energy needed to digest, absorb and metabolize that food (which is about 10% of caloric intake)
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excited state
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when an electron in an atom has gained energy from electricity, heating, etc. extra energy released as light
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electromagnetic radiation
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consists of oscillating, perpendicular electric and magnetic fields that travel through space at the same rate
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spectrum
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distribution of intensities of wavelengths of frequencies of electromagnetic radiation emitted or absorbed by an object.
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wavelength |
distance between adjacent crests or troughs in wave
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frequency
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number of complete waves passing a point in a given period of time. waves per second--
# x 10^x S^-1
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sound wave intensity=
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loudness--amplitude--height of wave
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green light
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495 nm
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planks quantum theory
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packets of energy released
E=hv
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to find energy with planks constant formula:
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E=hc/wavelength
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when energy gets higher, wavelength gets:
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smaller
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photoelectric effect
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such metals emit electrons when illuminated by light of certain wavelengths
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dual nature
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light has wave and particle characteristics
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wave theory fails and succeeds at explaining what about light?
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fails: photoelectric effect
succeeds: refraction of light by a prism
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Bohr model
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used plancks quantum theory to explain the behavior of an electron in a hydrogen atom
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continuous spectrum
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light of all wavelegths in visible region
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line emission spectrum
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only a few wavelengths (lines) are seen
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simplest line emission spectrum:
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hydrogen
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visible light in nm
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400-700
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principle quantum number=
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n= number of orbits or energy levels
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energy is emitted when:
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electron returns from excited state to ground state--this emitted energy is called a photon
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uncertainty principle
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it is impossible to simultaneously determine the exact position and the exact momentum of an electron
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electron density
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gives the probability that an electron will be found in a particular region of an atom
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boundary surface
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1 in 10 chance that the electron would have no definent boundry
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M sub l
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can have any integer number between l and -l
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l value for any s subshell
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zero
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the total number of atomic orbitals in a shell=
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n^2
ex: n=3: 3s+3p+3d=9
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n relates to the atomic orbitals:
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size |
l relates to the atomic orbitals
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shape
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m sub l relates to the atomic orbitals
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orientation
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s shape is
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spherical
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p shape is
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dumbbell shaped, at right angles with each other. two lobes--electron density on either side of nucleus
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each electron in an atom can exist in one of two possible spin states
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clockwise and counterclockwise
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spins opposite in direction produce
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oppositely directed magnetic fields--resulting in slightly different energies
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slight difference in energy created between electrons spins results in
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splitting the spectral lines into closely spaced pairs
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parallel spins
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same m sub s quantum number (both -1/2 or +1/2)
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paired spins
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same atomic orbital with opposite spins (on with +1/2 and other with -1/2)
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pauli exclusion principle:
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no more can two electrons can occupy the same atomic orbital in an atom, and these electrons must have opposite spins (no two electrons in the same atom can have the same set of four quantum numbers, n, l, m sub l and m sub s
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atomic orbital can hold a maximum of how many electrons?
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2 pairs
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each principle energy level, n, can accommodate a max number of
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2(n^2) electrons
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within a principal energy level n, there are ___atoomic orbitals
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n^2
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within a principle energy level n, there is a maximum of ____ electrons
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2n^2
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radial distribution plot
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graph of the electron density (probability 90-10)
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3s orbital boundary has greater volume and radius than
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2s
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d shape
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4 lobes that lie on a plane (x, y, or z)
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the atomic numbers of elements increase in numerical order from
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left to right
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atoms of a particular element contain one more electron and proton than the atom ____ that element
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preceding |
parallel spins minimize
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electron-electron repulsion, making total energy of the set of electrons as low as possible
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hunds rule
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the most stable subshell has the maximum number of unpaired electrons, all with the same spin
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when two subshells have the same n+l value...
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electrons are first assigned to the subshell with the lower n value
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half-filled subshells minimize
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electron repulsion
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elements in the same group in the periodic table have similar
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chemical behavior and valence electron configurations
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the dots in a lewis dot structure are
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the valence electrons
given by A-group
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s block elements
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1A and 2A
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p block elements
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3A - 8A
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Group 1a -3a form
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positive ions (cations) with charges = to their group numbers
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nonmetals in 5A-7A form
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ions by adding electrons to form negative ions (anions) with charges = to 8 minus their A group number
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atoms in group 1A, 2A and 3A
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lose an electron to form 1+ 2+ and 3+
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atoms in groups 7A 6A and some in 5A gain 1 2 or 3 electrons to form
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1- 2- and 3-
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negative ions have the same electron configuration as the____noble gas
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next |
isoelectric |
atoms and ions that have the same electron configuration
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when forming cations in the d section, always take from the
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n+1 s
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diamagnetic |
all electrons are paired (shells are full) and spin oppositely so their magnetic field cancels out--very weakly repelling
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paramagnetic
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unpaired electrons are attacked to magnetic field, the more unpaired electrons, the stronger the attraction.
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ferromagnetic
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permanent magnets. spins of unpaired electrons in a cluster of atoms in a solid are all aligned in the same direction
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only metals that are ferromagnetic
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nickel, cobalt, iron
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for main group elements, atomic radii increases going ____ a group
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down |
for main group elements, atomic radii _____ going across the period
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decrease
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transition elements in neighboring groups tend to be more alike in their properties than elements in their____
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groups |
screening effect
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the inner electrons shield or screen the valence electrons from the + charge or the protons in the nucleous
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effective nuclear charge
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Z*= positive charge on nucleous - the repulsion between electrons on each other
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effective nuclear charge increases from___ to ___.
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left to right
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ionization energy increases from ____ to ___
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left to right
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when an electron is removed...
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atom shrinks because there are fewer electrons to repel each other in comparison to the protons that pull them in
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electron affinity
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energy change when an electron is added to a gaseous atom to form a 1- atom
it measures the attraction an atom has for an additional electron
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fluorine and the rest of the halogens have large negative Electron affinity because
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by acquiring an electron the halogen atoms achieve stable octet
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electron affinities become more ____ across the periodic table
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negative
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metals tend to
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lose electrons
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nonmetals tend to
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gain an electron
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heated solid objects emit
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continuous spectra
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excited atomic gasses emit
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line spectra
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photon always carries
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positive energy
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De Broglie Wavelength
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all moving objects act as waves
at a node, amplitude of wave = 0
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order of wavelength lowest to highest wavelength
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gamma ray, x ray, UV, blue, green ,red, IR, Microwave, Radiowaves
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blue
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400
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red
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700
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black body spectra
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--light emitted by heated objects
--wavelength spectrum depends primarily on temp
--intensity and color depends on temp
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in blackbody radiation higher temp=
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shorter wavelength
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in enthalpy, reversing an equation changes the ___ but not the ___ of delta H
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sign, magnitude
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state defined by:
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volume, temp, pressure, composition, mass
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Delta E = q sub v
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only true if staying at constant volume
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only true if staying at constant volume
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0 |
specific heat capacity of water is higher or lower than most common elements?
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higher
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