Download ARRANGEMENT OF ELECTRONS IN ATOMS

ARRANGEMENT OF ELECTRONS IN ATOMS
4-1 The development of a New Atomic Model
Properties of light
- __________________________________________________ - a form of energy that exhibits wavelike behavior
as it travels through space
- examples: visible light, X rays, ultraviolet and
infrared light, microwaves, and radio waves
- move at 3 x 108 meters per second (m/s)
through a vacuum and slower through matter
- _________________________________________________ - all the forms of electromagnetic radiation put
together
- Wave motion is repetitive:
- ______________________________ () - the distance between corresponding points on adjacent waves
- meter, centimeter, or nanometer (1 nm = 1 x 10 -9 m) is unit
for measuring
- ________________________________ ( v ) - the number of waves that pass a given point in a specific
time, usually one second
- waves/second; 1 wave/second = ________________ (Hz)
- The distance between any 2 corresponding points on one of these water waves, such as from crest to crest,
is the wave’s ________________________________,  . We can measure the waves’ frequency, v, by
observing how often the ___________________________________rises and falls at a given point, such as
at the post.
- Frequency and wavelength are related to each other:
c =
v
(c = speed of light) (the product
v is a constant) (  is inversely proportional to
v; so the wavelength of light ________________________________, frequency ___________________)
_____________________________________________________ - the emission of electrons from a metal when light shines
on the metal
- involved the frequency of the light striking the metal,
ejecting electrons and creating an electric current
- __________________________ - the minimum quantity of energy that can be lost
or gained by an atom
- E = hv
(E = energy in joules;
h = constant, 6.626 x 10-34 J s;
v = frequency of radiation emitted)
Each of particle of light carries a quantum of energy. These particles are called __________________________ - a
particle of electromagnetic radiation having zero mass and carrying a quantum of energy.
The energy of a particular photon depends on the frequency of the radiation
E photon = hv
In order for an electron to be ejected from a metal surface, the electron must be struck by a single photon
possessing at least the minimum energy required to knock the electron loose. The minimum
energy corresponds to a minimum frequency. Electrons in different metal are bound more or less
tightly, so different metal require different minimum frequencies to exhibit the photoelectric
effect.
Hydrogen-Atom Line-Emission spectrum
- When current is passed thru a gas at low pressure, the potential energy of some of the gas atoms
increases.
- ___________________________________________ - lowest energy state of an atom
- _________________________________________ - a state in which an atom has a higher potential energy than it
has in its ground state
- example: neon light - when an excited atom returns to its
ground state, it gives off the energy it gained in the form of
electromagnetic radiation; a colored light
- ________________________________________________ - when a narrow beam of the emitted light was shined
through a prism, it was separated into a series of
specific frequencies, or bands of light, (and
therefore specific wavelengths) of visible light
- _______________________________________________________ - the emission of a continuous range of
frequencies of electromagnetic radiation
- When an excited atom with energy E2 falls back to energy E1, it releases a photon that has energy
E2 - E1 = Ephoton = hv
Bohr Model of the hydrogen atom
- the model linked the atom’s electron with photon emission
- the electron can circle the nucleus only in allowed paths or orbits
- when the electron is in one of these orbits, the atom has a definite, fixed energy. The electron, and therefore the
hydrogen atom, is in its lowest energy state when it is in the orbit closest to the nucleus. This orbit is separated
from the nucleus by a large empty space where the electron cannot exist. The energy of the electron is higher when
it is in orbits that are successively farther from the nucleus.
- while in an orbit, the electron can neither gain or lose energy It can, however, move to a higher energy orbit by
gaining an amount of energy equal to the difference in energy between the higher-energy orbit and the initial lowerenergy orbit. When a hydrogen atom is in an excited state, its electron is in a higher-energy orbit. When the atom
falls back from the exited state, the electron drops down to a lower-energy orbit. In the process, a photon is emitted
that has an energy equal to the energy difference between the initial higher-energy orbit and the final lower-energy
orbit.
4-2 The Quantum Model of the Atom
____________________________________________ - bending of a wave as it passes by the edge of an object
________________________________________ - overlapping of waves which results in the reduction of energy in some
areas and an increase of energy in others
_______________________________________________________________ - it is impossible to determine simultaneously
both the position and the velocity of an
electron or any other particle
___________________________________________________ - describes mathematically the wave properties of electrons
and other very small particles
- solutions are known as _____________________________
_____________________________ - a 3-D region around the nucleus that indicates the probable location of an electron
- have different shapes called sublevels
- _______________________________________ - specify the properties of atomic
orbitals and the properties of electrons in orbitals
- first three quantum numbers indicate the main energy level, the shape, and
the orientation of an orbital
1) PRINCIPAL QUANTUM NUMBER
- symbolized by n, indicates the main energy level
occupied by the electron.
- n = 1, 2, 3,. . . . .
- as n increases, electron’s energy and the
average distance from the nucleus
increases
- the total number of orbitals that exist in a given shell,
or main energy level, is equal to n2
2) ANGULAR MOMENTUM QUANTUM NUMBER
- symbol (l), which are assigned letters of s , p , d , f
- s = spherical
- p = dumbbell shaped
- d = complex
- f = very complex
- indicates the shape of the orbital
- for a specific main energy level, the number of
orbital shapes possible is equal to n
- the values of l allowed are 0 and all positive integers
< n-1
- second energy level, n = 2, has two
sublevels – the s and p, etc.
3) MAGNETIC QUANTUM NUMBER
- symbol m
- indicates the orientation of an orbital around the
nucleus
- s orbital is spherical and is centered
around the nucleus, it has only one
possible orientation, so m = 0
- p orbital has three along the x, y, or z
axis: px , py , pz
correspond in no particular order as to the
values of m = -l, m = 0, m = +1
- d orbital have five (one has a different
shape)
correspond to the values of m = -2,
m = -l, m = 0, m = +1, m = +2
- f orbital has seven
- the fourth, the spin quantum number, describes a fundamental state
of the electron that occupies the orbital
1) SPIN QUANTUM NUMBER
- has only two possible values – (+1/2, -1/2)
- indicates the two fundamental spin states of an
electron in an orbital
- a single orbital can hold a maximum of two
electrons, which must have opposite spins
Bohr: electrons of increasing energy occupy orbits farther and farther from the nucleus
Schrodinger: electrons in orbitals also have quantized energies
4-3 Electron Configurations
___________________________________________________ - arrangement of electrons in an atom
Electrons assume arrangements that have the lowest possible energies called the ____________________________________
_____________________________________________ - an electron occupies the lowest-energy orbital that can receive it
- 3d and 4s orbitals can have exceptions (half full is more stable) –
less energy is required for two electrons to pair up in the 4s orbital
than for a single electron to occupy a 3d orbital
_________________________________________________________ - no two electrons in the same atom can have the same
set of four quantum numbers
________________________________________ - orbitals of equal energy are each occupied by one electron before any
orbital is occupied by a second electron, and all electrons in singly
occupied orbitals must have the same spin