UW - Chem 142 Exam 1
Units 1 and 2
Terms in this set (117)
arrow drawn to show the uneven distribution of electrons in a bond or molecule, a molecule that has a center of positive charge and a center of negative charge.
De Broglie Wavelength
wavelength of an object is inversely proportional to its mass, or in other words, equation used to determine mass or wavelength when either of those and speed is given
a chart showing all the elements arranged in columns with similar chemical properties.
the capacity to do work or to produce heat
law of conservation of energy
energy can be converted from one form to another, but cannot be created or destroyed
energy due to position or composition
energy due to motion and mass and velocity of object
involves transfer of energy between two objects due to a temperature change
a force acting over a distance
a property of the system that depends only on its present state (energy)
when a reaction produces heat
when a reaction requires/absorbs heat
contains electrical and magnetic fields that simultaneously oscillate in planes
distance between 2 consecutive peaks/troughs in a wave
the number of waves (cycles) per second that pass a given point
6.62607 x 10^-34 Js = h
Used to determine energy gained or lost
energy comes in quantized "packets" of energy
EM radiation can be viewed as a stream of photons
phenomenon in which electrons are emitted from the surface of a metal when light strikes it
results when light is scattered from a regular array of points or lines
- colors result because various wavelengths are not scattered in the same way
Do electrons exhibit particle or wave properties?
All matter, not just electrons exhibits BOTH
electrons become excited via the breaking of bonds, and thus produce EM radiation
all wavelengths of visible light
shows specific lines of emission or absorption
- differs for each element
What are the energy levels available to the electrons in the Hydrogen atom?
E = -2.178 x 10^-18 J (Z^2/n^2)
In relation to the movement of electrons, when is energy released from a system?
As electrons move closer to the nucleus, Energy is released from the system and the overall energy lowers.
Quantum wave mechanics
approach developed by de Broglie and Schrodinger to replace the Bohr Model.
Why is the Bohr model wrong?
The Bohr model is wrong because it can only be applied to Hydrogen atoms (or one-electron systems). As the number of electrons increases, or rather, the entire number of atoms in the system, the model is too simple to account for these changes. In addition, we cannot know the exact position of the electron as it moves around the nucleus, and thus it is not appropriate to assume that the electron is moving around the nucleus in a well-defined orbit.
stationary waves because they do not travel the length
points of zero lateral displacement, located at either end of waves, and form as the frequency increases
used to describe the Hydrogen electron as a wave
the specific wavefunction for a given electron
Heisenberg Uncertainty Principle
there is a fundamental limitation to how precisely we can know both the position and movement of a particle at a given time, where delta(x) = uncertainty in position, delta(p)= uncertainty in momentum, and h = Planck's constant divided by 2pi
used to determine the position of the electron in 3D space, where n = principle #, l = angular momentum #, and ml = magnetic quantum #. In other words, these are orbital descriptors that arise when boundary conditions are applied.
What do we use to determine the energy of the system?
The principle quantum number, because as n increases, the orbital becomes larger and the electrons spend more time farther from the nucleus.
Why is it important that the principle quantum number is only in integers?
Energy is quantized, meaning that energy can only assume discrete values, which is achieved by a whole number for the principle quantum number.
Where is the highest probability of finding an electron?
As shown by the electron density map, the highest probability of finding an electron is nearest the nucleus, which drops rapidly as the distance from the nucleus increases.
radial probability distribution
imagine dividing the electron density maps into spherical shells and this is what you get. 90% of the total electron probability is enclosed in each specific sphere.
a set of orbitals with a given value of l, designated by giving the value of n and the letter for l.
available to all levels, sphere shaped, 1 orbital and max of 2 electrons
available to levels above 2s, dumbbell shaped because have 2 lobes separated by a node at the nucleus, 3 orbitals and max of 6 electrons
available to levels above 3p, 2 fundamental shapes, four of them being 4 lobes centered in the plane, and the other one being 2 lobes along z axis and a "belt" in xy plane, 5 orbitals and max of 10 electrons
available to levels above 4d, very complex, 7 orbitals and max of 14 electrons.
all orbitals with the same value of n have the same energy
Pauli exclusion principle
in a given atom, no 2 electrons can have the same set of 4 quantum numbers (n, l, ml, ms)
because of the Pauli exclusion principle, this has been introduced to allow for a maximum of 2 electrons per orbital with opposite spin
ms = +1/2
ms = -1/2
atoms with more than one electron
electron correlation problem
we cannot rigorously account for the effect a given electron has on the motions of the other electrons in an atom
as protons are added one by one to the nucleus to build up the elements, electron are similarly added to the atomic orbitals
the lowest Energy configuration for an atom is the one having the maximum number of unpaired electrons allowed by the Pauli principle in a particular set of degenerate orbitals. In other words, when drawing electron configurations, spread out the electrons as much as possible
the electrons in the outermost principal quantum level of an atom, or rather, the electrons we care about
the electrons in the inner principal quantum levels
forces that hold groups of atoms together and make the atoms function as a unit
the energy required to break the bonds
when a metal reacts with a nonmetal
the energy of interaction between a pair of ions, used to calculate the attractive and repulsive energy of two ions
the distance at which the Energy of the system is minimum
non-polar covalent bonding
a bond in which electrons are shared equally
polar covalent bonding
a bond in which the electrons are shared unequally
a bond in which the electrons are "transferred" from an atom that easily loses electrons to one that easily gains electrons
the ability of an atom in a molecule to attract shared electrons to itself
In relation to the periodic table, how does electronegativity increase?
In general, it increases from left to right and top to bottom, with Fluorine being the most electronegative element.
Localized electron model
a simple model that can be easily applied to very complicated molecules, assumes that a molecule is composed of atoms that are bound together by using atomic orbitals to share electron pairs
the pairs of electron localized on an atom
the pairs of electrons found in the space between the atoms
represents arrangement of valence electrons among atoms in a molecule
What do all atoms want to achieve to be stable?
All atoms want to achieve noble gas configuration, or in other words, a full valence shell with 8 electrons.
Hydrogen forms stable molecules where it shares 2 electrons
atoms that are surrounded by 8 electrons are stable and have full valence shells
What are the steps for writing or drawing Lewis Structures?
1. sum valence electrons of all atoms
2. use pairs of electrons to form bonds between each pair
3. arrange remaining electrons to satisfy duet rule and octet rule
invoked when more than one valid Lewis structure (in terms of placement of electrons) can be written for a particular molecule, resulting electron structure of molecule is given by the average of these structures
What is the defective assumption of the localized electron model?
It assumes that are electrons are localized. This is why resonance structures are sometimes required.
Lewis structures that contain the same atoms but in different bonding relationships
the difference between the number of valence electrons on the free atom and the number of valence electrons assigned to the atom in the molecule.
What is formal charge used for?
It is used to determine the most accurate Lewis structure out of several structural isomers
the 3D arrangement of atoms in a molecule
Valence Shell Electron Pair Repulsion model
a simple model that is useful in predicting geometries of molecules formed by non metals
What are the steps for drawing VSEPR models?
1. draw Lewis structure for molecule
2. count number of electron pairs around central atom and arrange them in the way that minimizes repulsions
3. determine position of atoms from way electron pairs are shared
4. name molecular structure from positions of atoms.
What is the dual nature of light?
Light can be seen as either a particle or a wave
a pattern produced by waves that have undergone diffraction
used in 3d models to show where there are higher probabilities of finding electrons
effective nuclear charge
The net positive charge experienced by an electron in a multi-electron atom
Middle of the table. Non-reactive metals. Variety of different metals.
elements from period 6 that follow the element lanthanum
in the periodic table, the f-block elements from period 7 that follow the element actinium
Main group elements
an element in the s-block or p-block of the periodic table
elements with properties that fall between those of metals and nonmetals
trough of a wave
Property of atoms: having the same number of electrons
relationship between wavelength and frequency
inversely related; the bigger the wavelength, the longer the frequency
order of the electromagnetic spectrum, smallest to largest frequencies using terms microwaves, gamma-rays, ultraviolet radiation, visible light, infrared radiation, radio waves, and x-rays
radio waves, microwaves, infrared radiation, visible light, ultraviolet radiation, x-rays, gamma rays.
two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei; differ in atomic mass but not in atomic number
atomic mass number
the number of protons plus the number of neutrons
number of protons in the atom