40S Unit 5: Atomic Theories Flashcards
describe John Dalton’s atomic theory
published in 1805 and it was the first atomic theory. it had 4 main parts:
1. all matter is made up of tiny solid, indivisible particle called atoms
2. all atoms of the same element are identical, and atoms of different elements are different
3. compounds are created when atoms from different types of elements combine in fixed proportions
4. atoms cannot be created or destroyed, or subdivided into smaller particles
describe J.J. Thomson’s atomic theory
his theory was that atoms were a positive solid sphere with much smaller negatively charged particles called electrons in them that can be removed. the number of negatively charged particles is equal to the number of positive charge in the solid atom.
explain the experiment that led J.J. Thomson to his theory
he applied a high voltage between 2 electrodes in a vacuum and discovered that negatively charged particles flowed from one electrode to another, leaving the previously neutrally charged electrodes either positively or negatively charged and proving that an atom was divisible into smaller parts
describe Ernest Rutherford’s atomic theory
in 1909 he carried out the gold foil experiment in which is shot alpha particles through a thin gold foil. he discovered that some of the alpha particles were deflected back at completely unexpected angles. he reasoned that such deflections could only occur if all the mass of the atom was concentrated in a tiny dense center that was smaller than the atom. in 1911 he published his findings and introduced the nuclear model of the atom where the nucleus contained positive particles he called protons and electrons orbiting the nucleus with the vast majority of the atom being empty space.
who discovered the neutron
James Chadwick, a student of Rutherford’s. he discovered the neutron in 1932 through his investigation of isotopes
what is an isotope
isotopes are atoms of the same element that have the same atomic number, but different atomic masses
why are isotopes significant?
they can be radioactive and radioactive substances can emit powerful energies like alpha particles, beta particles or gamma rays from the nucleus of the atom
describe Neils Bohr’s atomic theory and explain the experiments he performed
Bohr’s theory said that electrons orbit the nucleus in very specific energy levels that he called ‘principal energy levels’. the electrons could exist at each level but they could not exist in between a level. he found that when gases were excited, they emitted light and that light formed a very specific spectral band distribution rather than a spectrum.
who is credited with started the quantum theory process with his investigation of black bodies
Max Planck with his investigation and analysis of black body radiation
use the Bohr theory to explain hoe it is possible for an atom to emit light
atoms are able to emit light when their electrons get excited through the addition of energy. the excited electrons jump up to a higher energy level equivalent to the amount of energy absorbed. later the same electron falls back down to its original resting state, and gives off light equivalent to the difference in energy levels. the frequency of light emitted can be determined using the ΔE = nhf. the greater the drop the greater the energy and frequency, thus the colours of the spectral lines indicate the amount of change in energy experienced by the electron producing the photon
what is the photo electric effect
the effect of using light to eject electrons off of a metal plate as discovered by Albert Einstein in 1905. it led to his notion that light waves behaved as particles in a wave-particle package he called a photon
what is a photon
a wave-particle package that is able to transport energy through a variety of mediums including a vacuum. a beam of light is made up of a stream of photons
identify the colours of a rainbow in terms of energy, from highest energy frequencies to lowest
violet
indigo
blue
green
yellow
orange
red
high energy implies ________ frequency and _____ wavelengths
high, small
why was the Bohr model replaced by the quantum model
the biggest reason was the discovery that there were actually energy levels within energy levels, and thus the Bohr model with only principal energy levels was not enough
what was the evidence that led to the secondary quantum number
when spectral lines were examined, they discovered that there were lines within lines. Arnold Sommerfeld later explained this phenomena using elliptical, rather than circular orbits. the second quantum number is given the symbol ‘l’
what was the evidence that led to the magnetic quantum number
the discovery that there were even more energy subdivisions that became evident when the spectral emissions were passed through a strong magnetic field. it is given the symbol m subscript l
what was the evidence that led to the spin quantum number
Wolfgang Pauli discovered through the investigation of paramagnetic materials that the very slight magnetic effects were caused by the spin of the electron. there are only 2 ways an object can spin, clockwise or counter-clockwise and he called one spin +1/2 and the other -1/2
describe 4 ways in which orbitals are different from orbits
- orbits are circular or elliptical while orbitals can exist in a variety of shapes
- orbits are 2D while orbitals are 3D
- orbits involve a solid electron that goes around and around while orbitals involve a standing wave of electrons energy state
- orbits can be described using simple math and classical physics while orbitals need to be described using more complicated equations like the Schroedinger equations
what do the letters s, p, d and f represent and how many electrons can each level hold
s - sharp - 2 electrons max
p -principal - 6 electrons max
d - diffuse - 10 electrons max
f - fundamental - 14 electrons max
what is the Aufbau principle
it states that electrons will always fill the available energy levels starting by filling the lowest energy levels first
what is the Pauli exclusion principle
it states that when electrons pair up to fill an orbital, they always do so such that they each have a opposite spin, two electrons of the same spin, two electrons of the same spin do not occupy the same orbital ever
what is Hund’s Rule
it states that when electrons are filling the various orbitals in a given energy level, they each occupy their own orbital until they are forced to share
what is the valence shell
the valence shell is composed of electrons in the highest principal quantum number. this is why all the elements in the transition metals and inner transition metals only have 2 electrons in their valence shell. it is also why the octet rule exists, because the valence shell is formed by the s and p orbitals of a given principal energy level
