The Structure of the Atom

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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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Gold Foil Experiment7

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

Shells, Orbitals and Erwin Muller

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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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Think ActivityLet’s see if we can figure out some patterns.

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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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Element Spectroscopy

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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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Practice Shells

Let’s draw some atoms based on old ideas

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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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New Eyes

Filling orbitals and how to write electron configuration

Let’s Practice

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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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