40S Unit 5: Atomic Theories

Question 1

describe John Dalton’s atomic theory

Answer 1

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

Question 2

describe J.J. Thomson’s atomic theory

Answer 2

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.

Question 3

explain the experiment that led J.J. Thomson to his theory

Answer 3

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

Question 4

describe Ernest Rutherford’s atomic theory

Answer 4

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.

Question 5

who discovered the neutron

Answer 5

James Chadwick, a student of Rutherford’s. he discovered the neutron in 1932 through his investigation of isotopes

Question 6

what is an isotope

Answer 6

isotopes are atoms of the same element that have the same atomic number, but different atomic masses

Question 7

why are isotopes significant?

Answer 7

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

Question 8

describe Neils Bohr’s atomic theory and explain the experiments he performed

Answer 8

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.

Question 9

who is credited with started the quantum theory process with his investigation of black bodies

Answer 9

Max Planck with his investigation and analysis of black body radiation

Question 10

use the Bohr theory to explain hoe it is possible for an atom to emit light

Answer 10

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

Question 11

what is the photo electric effect

Answer 11

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

Question 12

what is a photon

Answer 12

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

Question 13

identify the colours of a rainbow in terms of energy, from highest energy frequencies to lowest

Answer 13

violet
indigo
blue
green
yellow
orange
red

Question 14

high energy implies ________ frequency and _____ wavelengths

Answer 14

high, small

Question 15

why was the Bohr model replaced by the quantum model

Answer 15

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

Question 16

what was the evidence that led to the secondary quantum number

Answer 16

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’

Question 17

what was the evidence that led to the magnetic quantum number

Answer 17

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

Question 18

what was the evidence that led to the spin quantum number

Answer 18

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

Question 19

describe 4 ways in which orbitals are different from orbits

Answer 19

1. orbits are circular or elliptical while orbitals can exist in a variety of shapes
2. orbits are 2D while orbitals are 3D
3. orbits involve a solid electron that goes around and around while orbitals involve a standing wave of electrons energy state
4. orbits can be described using simple math and classical physics while orbitals need to be described using more complicated equations like the Schroedinger equations

Question 20

what do the letters s, p, d and f represent and how many electrons can each level hold

Answer 20

s - sharp - 2 electrons max
p -principal - 6 electrons max
d - diffuse - 10 electrons max
f - fundamental - 14 electrons max

Question 21

what is the Aufbau principle

Answer 21

it states that electrons will always fill the available energy levels starting by filling the lowest energy levels first

Question 22

what is the Pauli exclusion principle

Answer 22

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

Question 23

what is Hund’s Rule

Answer 23

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

Question 24

what is the valence shell

Answer 24

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

Question 25

why is the valence shell important

Answer 25

it is important because the valence shell determines the main chemical properties of the element, and it is also why elements in the same vertical column of the periodic table are called members of a family in that they all share similar chemical behaviours

Question 26

what is the importance of Louis de Broglie’s idea of reversing Einstein’s light waves can behave as particles, into particles like electrons can behave as waves

Answer 26

it helped in explaining why electrons can only exist in certain particular energy levels, and why the energy levels jump in quantum amounts. the wave nature of the electron causing standing waves and standing waves can only exist in integer increments, each one a significant ‘lap’ in more energy than its previous level. electrons cannot exist at the in between amounts for that same reason that standing waves cannot exist at 4.75 wavelengths only 4 or 5 wavelengths.

Question 27

explain why electrons in the p orbital for instance, can move from side to side without ever being able to be found in between

Answer 27

electrons can travel back and forth between the 2 sides of the hour-glass shape and never be found in the middle because the superposition of a crest and a trough results in the appearance of no waves, when in fact there are two waves present at the same time, but they cancel each other out

Question 28

what is the difference between the 2 main philosophical approaches of idealism an materialism

Answer 28

1. idealism believes in the supremacy of the spirit/soul over the material world
2. materialism believes in the dominance of he material world, believing consciousness and spirit to be simple a manifestation of particles interacting

Question 29

what are 5 key differences between classical and quantum physics

Answer 29

1. in classical physics, energy is continuous and was thought to exist at any level or interval. a graph of energy versus intensity was thought to be a perfectly continuous and straight line. in quantum physics, the minute level energy increases in small increments called quanta. this was discovered thrugh Max Plank’s investigation of black bodies
2. in classical physics, all waves were thought to be formed by continuous oscillations. in quantum mechanics, Albert Einstein discovered that light waves behave as discreet particles, and thus introduced the concept of the photon which is simultaneously like a particle and like a wave
3. in classical physics, waves and particles were 2 independent phenomena with the electron being a particle with mass and charge. in quantum mechanics, Louis deBroglie discovered that the electron is a wave with mass and charge
4. in classical physics, objects orbit in 2D circular or elliptical orbits. in quantum mechanics, the electrons orbit the nucleus in 3D orbital clouds where the location of the electron can be guessed at using probabilities
5. in classical physics, the location of where an object could theoretically be known with complete certainty. in quantum mechanics, the location of the electron can only be known with probabilities. Erwin Schrodinger developed a set of wave equations to mathematically determine these probabilities