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The Atom as Matter
Dalton’s atomic theory had problems
It considered atoms to be hard, indivisible particles
Did not explain why atoms reacted
Also did not explain why atoms had varying abilities to combine with each other
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Need for a New TheoryContinued research on the nature of the atom after 1885 led to more understanding of the atomic structure
Scientist of importance included
Becquerel
Thomson
Rutherford
Chadwick
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Parts of the Atom
Three fundamental particles
Protons
Neutrons
Electrons
The number and arrangement of these three particles determines the nature and properties of the different kinds of atoms.
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ElectronDiscovered by J.J. Thomson in 1897
Represented with a negative sign, or e, e-
Has the mass of only 1/1837th that of the hydrogen atom
Name is derived from Greek “elektron”- means amber- rub a piece of amber with fur or wool, it will attract light objects
Cause of attraction is an electrical charge
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Protons
Discovered by Ernest Rutherford in 1919
Represented with a + sign, the letter p, or p+
Charge is equal and opposite of an electron
Mass is 1836/1837 that of an Hydrogen atom
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Neutrons
Discovered by James Chadwick in 1932
Represented with the letter n, 0, n0
They have no charge, thus they are neutral
has about the same mass as that of a proton
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Summation of the Parts
Particle Symbol Charge Mass in amu
Location in Atom
Electron e, -, e- Negative, -1 0.00055 Surrounding
the nucleus
Proton p, +, p+ Positive, +1 1.00732 Inside the Nucleus
Neutron n, 0, n0 Neutral, 0 1.00866 Inside the Nucleus
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The Electron Theory of Atomic Structure
Understand that the knowledge and understanding of the structure of the atom is not by direct observation but rather how the energy is absorbed or given off by large number of atoms
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Terminology
Atoms are described by scientist in terms of particles and energy due to this phenomenon
We will discuss this idea in more detail later
Called Quantum Mechanics
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ModelOne of the first major developments in this model is derived from
Niels Bohr
came up with the idea of a nucleus and shells of electrons
Postulated that a strong electrical force kept the tiny universe intact
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The AtomNucleus= where protons and neutrons are found at
Positive charge
most massive area
Then a “Cloud” of electrons orbiting outside of the nucleus
negative charge
areas where electrons are relatively found at are called shells or energy levels
Electrons spin on their axis13
The IdeaThe idea was that there was a shell
general region of electron movement around the nucleus
Electrons generally stay in the region unless they are excited
Each shell or region is a specific distance
Orbitals are the paths that the electron goes within a shell
Erwin Muller helped in this by photographing the location of atoms in metal crystals
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ElectronsElectrons also spin while they revolve
This spinning creates a magnetic field
Electrons that spin opposite of one another are attracted to each other (Just like magnets)
Pauli exclusion principle (1925)- no more than 2 e- can occupy the same orbital (Due to Spin)
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Orderly Arrangement of Electrons
Each atom has one or more shells depending upon the number of protons and electrons
Since orbitals are limiting, then there are only a certain number of electrons that can fit in one orbital
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Think
Think about the periodic table and all that you have learned before
What is the maximum capacity of this orbital?
Based on Pauli Exclusion Principle, what is true about the spins?
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Energy Sublevels or Subshells Quantum Mechanics aka Quantum Theory
Niels Bohr- 1913- developed the theory that electrons revolve at definite energy levels, and this is the basis of Quantum Theory
In order for an electron to move it must gain or lose energy
The amount of energy an electron must give off or take on is the difference between its original energy level and the one below it or above it
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How to See itWe can see this change by using a spectroscope
we see the light being emitted as the electron changes its orbital
This is the foundations of quantum theory
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TransformationOverall this change of energy is a change from electrical energy or heat into light
the color (energy) of the light depends upon the change or changes in energy levels made by the electrons
The jumps from outer to inner energy levels are revealed by the characteristic lines observed for different elements in the spectroscope
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The s, p, d, f
In orbitals you have subshells (energy sublevels)
We designate these levels with letters like s,p,d,f
Get out your Periodic Tables
All electrons within a specific energy sublevel have the same amount of energy
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s- Orbitals
Smallest amount of energy
the other orbitals will have increasing energies
these levels have definite amounts or packets of energy also called quantum
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p, d, and f
Let’s take a look at the periodic table and lets see how this all fits
Remember how I taught you to fold the periodic table- now we use it again
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Atomic Structure
The number of electrons in any atom equals the number of protons
Atomic Number
this determines the element!!!!
Great way to classify elements into an orderly arrangement called the periodic table
ground state is always neutral (protons equal electrons)
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Chemical ActivityAtoms with a full octet or filled outer shells
do not combine with other atoms
they are inert
Noble gases
Incomplete filled shells tend to combine with other kinds of atoms whose shells are also not filled
do this by sharing, gaining, or losing electrons
Chemical activity is determined by outermost electrons also called valence electrons
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Three Rules of Filling
Electrons always occupy orbitals of the lowest energy available
There can be a maximum of only two electrons in any given orbital. (spins will be opposite- Pauli’s Exclusion principle)
Electrons are added successively filling subshells with electrons in a specific order based on increasing energies of the subshells.
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Last Items
What are Isotopes. We have been looking at the periodic table and the Atomic Mass Unit is not an even number.
Why
Those numbers are based on the abundancy of the isotopes.
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Isotopes
Isotopes- an element that varies due to number of neutrons
Remember that the element is determined by the number of protons.
Isotopes have different weights and this difference can cause some elements to have different radioactivity
note that the chemical properties remain virtually the same
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Calculations of Neutrons
Take the difference between Atomic Mass and Atomic Number in order to determine the number of neutrons
AN Isotope would be like
C12 and C14
C14 is the isotope because C12 is the norm
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Antimatter1929 Dirac made a prediction that there must exist “extraordinary” electrons or particles that have the same mass but are opposite in charge.
3 years later Anderson proved that there were positrons
These particles make up antimatter and may be controlled by antigravity
More can be found at Antimatter:Mirror of the Universe
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