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Atomic Theories
Democritus hypothesized that atoms are matter that can’t be cut anymore
John Dalton
billiard ball model
element consist of atoms
atoms cannot be created, destroyed, or divided
atoms of same element have identical size, mass, and properties
J.J Thomson
Plum puddling model
discovered the electron
used a high-voltage, evacuated glass tube to discover that cathode rays were streams of negatively charged particles, which he called electrons
Robert Millikan
found the mass of the electron
used charged oil droplets to determine the charge on the electron
he adjusted the voltage across 2 charged plates so he could halt the fall of the oil drops
then he calculated the charge on the oil drop therefore he calculated the mass of an electron
Henri Becquerel
demonstrated that uranium atoms are capable of spontaneously emitting energy, particles, or waves that travel through space
this is called radioactivity
3 types of radioactive emissions
Alpha particles (He2+)
Beta particle (e-)
Gamma ray
Ernest Rutherford
the nucleus
using gold foil experiment
he concluded the atom had a nucleus (a dense, possibly charged center made of protons)
electrons orbited the nucleus
Chadwick
the neutron
calculated the mass of a nuclei but the calculations didn’t match the associated charge. He concluded that missing mass is neutrons
Classical Theories of Light
it was believed that light existed as a steam of particles
Huygens proposed that light is a wave (refraction, reflection, and diffraction support the wave theory of light)
Maxwell proposed that light existed as an electromagnetic wave (known as the electromagnetic spectrum)
Hertz
the photoelectric effect - electrons are emitted by matter that absorbs energy from shortwave electromagnetic radiation
it was believed that the intensity of light shining in metal determines kinetic energy of the electrons emitted
hertz said it’s the colour of light
Planck
Quantum
when a solid black object is heated it glows red, white then blue
Planck noticed it reached a peak then decreased
this signified that energy can be gained or lost in whole number multiples
light was emitted in bursts not a stream
light behaves as a particle
Einstein
photons - EM radiation is a stream of particles called photons (units of light energy)
Problems with Bohr’s planetary model
if electrons were accelerating, photons of electromagnetic radiation should be emitted
this would result in the electron being attracted towards the nucleus and collapsing into it
Spectroscopy
study of light
By looking at the patterns of light absorbed or emitted, scientists can identify what a substance is made of and learn about its structure.
Dark line spectrum
happens when white light passes through a cooler gas.
analyze what’s left
The Bohr atomic model
Electrons orbit the nucleus in fixed paths (like planets around the sun).
Each orbit has a specific energy level.
Electrons can jump to higher or lower orbits by absorbing or releasing energy (as light).
The light released makes up an element’s spectrum.
Successes of bohrs model
his model gives a reasonable explanation for mendeleev’s periodic law: periods result from the filling of electron energy levels
max electrons in each energy level correspond to number of elements in each period
explained the line spectrum of hydrogen
Failures of Bohrs model
could not predict the spectra of ions of more than one electron
Louis de broglie
de Brogloe
if light can behave like a particle, then any particle should also be able to act like a wave
therefore, electrons have wave properties
Erwin Schrodinger
used math and statistics
He proposed the quantum mechanical model of the atom.
Instead of electrons moving in fixed orbits (like Bohr said), Schrödinger showed that electrons exist in regions called orbitals—areas where they’re most likely to be found.
Heisenberg Uncertainly Principle
you can’t know both the exact position and speed of a particle at the same time.
Orbitals vs Orbits
Orbitals
2 electrons
3D
Distance from the nucleus varies
No set path
Orbits
2n² electrons
2D
Distance from the nucleus is fixed
Path is elliptical or circular
Pauli Exclusion Principle
no two electrons have the same four quantum numbers
quantum
Aufbau Principle
an energy level must be filled before moving on to the next higher energy level
Hund’s rule
each orbital at the same energy level must have one electron in it before any orbital can contain two electrons
Exceptions in electron configurations
Chromium, Silver and copper
Cu: [Ar] 4s^1 3d^10
Ionic compounds
electrons are transferred to elements w higher electronegativity
ionic bond is between oppositely charged ions
isoelectric - having the same number of electrons
Molecular compounds
form because of attractions of electrons from one atom to the nucleus of the other
atoms share electrons
non-polar molecules
only has non-polar bonds (no dipole)
when the sum of the individual bond dipoles is zero (they cancel each other out)
dipole- dipole
attract each other by lining up so their opposite ends are together
in a liquid, dipoles attract and repel each other, so an equilibrium has to be reached
Hydrogen Bonding
strong dipole-dipole force
Hydrogen is covalently bonded to a highly electronegative atom (N,O, F) no Cl
hydrogen is attracted to the partically negative charge on a neighbouring molecule
how does hydrogen bonding affect a substance’s physical properties
a substance
they increase boiling points
important in bio and organic molecules
no hydrogen bonds = no life
proteins and DNA would not exist as they rely on hydro bonds for structure
London Dispersion
between non-polar molecules
an increase as molecular mass increases (increases boiling points)
explains why noble gases can freeze to form solids
intermolecular forces + physical properties
strengths on bonds:
Ionic>Hydrogen bonds>dipole-dipole>london dispersion
stronger the bond, the higher the boiling point, melting point, surface tension, and viscosity
4 types of solids
Ionic solids
Metallic solids
Molecular solids
Network solids
Ionic Solids
Form between the interaction of a metal with a non-metal ion
strong ionic bond holds them together
properties: Hard, brittle, dissolves in water, high melting point, good conductor of electricity when dissolved
Metallic Crystals
closely packed metal atoms held together by electrostatic interactions and free-moving electrons
common properties: shiny, good conductor of thermal energy and electricity
don’t have similar properties as each other (electron sea theory)
electron Sea theory
metals are composed of closely packed atoms whose valence electrons are free to move
positively charged nuclei are fixed while the electrons are mobile
as electrons move from one positive nucleus to another, they hold the positively charged nuclei together
molecular crystals
similar to ionic crystal lattice but more complex
ex: ice can form many different crystals (snowflakes)
intermolecular forces will determine its structure and properties
intermolecular force is london-dispersion, resulting in lower melting points, less hard, doesn’t conduct electricity well
Covalent network crystals
ex: diamonds
strong intermolecular forces are working
electrons don’t move freely
properties: very high melting point, extremely hard, not good conductor on electricity
Carbon
carbon atoms can form different structures
this causes structures that are formed from carbon to have different properties
c
Diamonds
carbon forms a tetrahedral structure
very hard, not good conductors of electricity
Graphite
has a trigonal planar arrangement also forms hexagonal sheet between layers - contains strong covalent bonds in the plane and weaker london-dispersion between the graphite sheet layers)
bc of arrangement, electrons can break loose
slippery, black, good electrical conductor
Quartz
Made of silicone and oxygen (SiO2)
when silica is heated and cooled it forms quartz glass, a more disorganized structure