Ch 8 - Quantum Model of the Atom

wavelength

the distance between the 2 corresponding points on the wave

frequency (v)

the number of the crests (or troughs) that pass a given point per second

what is the unit for frequency?

s^-1 or Hertz (Hz)

light 

a form of energy that can be described as a moving wave of magnetic and electrical potential

visible light 

the light that can be perceived by the human eye 

refract

to change the direction of light, usually through a prism 

how are wavelength and frequency related?

inversely proportional

what is the speed of light?

• c = 2.99 × 10⁸ m/s

frequency x wavelength =

c

What happens if you shine a beam of light onto a metal surface in a vacuum?

electrons will be ejected

what is the brightness of light proportional to?

the number of electrons ejected

photoelectric effect

the phenomenon of electrons being ejected when a beam of light shines onto a metal surface 

photoelectrons

the electrons emitted when light is shone on a metal surface

photons

packets or particles of light

light is both…

• a wave 

• a steam of particles 

• wave-particle duality of light 

How do low energy photons correspond to light?

with a long wavelength and low frequency

How do high energy photons correspond to light?

with short wavelengths and high frequency

Planck’s constant

h = 6.626 × 10^-34 Js

E =

hv = hc/wavelength

light absorption

occurs when an atom absorbs light energy from surroundings and gains energy 

light emission

occurs when an atom has excess energy and gives off energy by emitting light

emission spectrum

results when energy is absorbed by an atom and them released as light

Why is the emission spectrum unique?

• bc the spacing between the electronic energy level is different for each type of atom

What does the atomic spectrum of H include?

• continuous spectrum 

• line spectrum 

continuous spectrum

a continuous spectrum containing all wavelengths of visible light

line spectrum

a H line spectrum contains only a few discrete wavelengths

the Bohr Model

• H consists of a central proton about which moves an electron in a circular orbit 

• electrons can only occupy fixed orbits around the nucleus 

• fixed orbits have discrete energies 

• as the orbit gets father from the nucleus, the energy increases 

the equation for the energy different between two states

ΔE = -2.18 × 10^-18 J (1/n²_f -1/n²_j) 

ground state

(n=1) the lowest energy state for the single electron present in H

excited state

(n>1) any other states for the electron of H

What are the accomplishments of the Bohr Model?

• explains the structure of the H atom 

• determined that the location of electrons in an atom is restricted to fixed locations called orbit 

What are the drawbacks of the Bohr Model?

• it’s impossible to specify the precise position of an electron in an atom at a given instant

• the model deviates significantly from that observed by experiment when applied to atoms with 2 or more electrons

atoms and electrons have both…

wave and particle properties

quantum numbers

a series of numbers that describe various properties of an orbital, required to describe the distribution of electron density in an atom

principial quantum number

(n) 1-7 integer values, related to the size and energy of an orbital, as increases the size and energy increase 

shell 

a collection of orbitals with the same value of n 

angular movement quantum number

(l) related to the shape of atomic orbitals

when l = 0…

s (2 electrons max)

when l = 1

p (6 electrons max)

when l = 2

d (10 electrons max)

when l = 3

f (14 electrons max)

subshell

a collection of orbitals with the same value n and l

magnetic quantum numbers 

(m_l) related to the orientation or direction of orbitals, important for forming bonds 

spin quantum number

(m_s) related to the spin of electrons, can either be +1/2 or -1/2,

when m_s = +1/2

there is a parallel electron spin

when m_s = -1/2

there is an antiparallel electron spin

orbital diagrams 

graphical representations of the subshells of an atom, in which each subshell is separated vertically from the others in order of increasing energy 

electron configuration

describes how the electrons are distributed in various atomic orbitals