The+Atom

= The Atom = = =



__ Early Models of the Atom __

 * ==== Particles that make up matter are microscopic ====
 * ====** Atom ** : the smallest particle of an element that retains its identity in a chemical reaction ====
 * ==== [[image:Picture_9.png width="175" height="179"]] ====
 * ====__ Democritus’s Atomic Philosophy __====
 * ==== Democritus was one of the first to propose the existence of atoms ====
 * ==== He believed they were indivisible and indestructible ====
 * ==== His ideas did not explain chemical behavior, nor did they provide experimental support as he did not follow the scientific method ====
 * =====__ Dalton’s Atomic Theory __=====
 * John Dalton was an English chemist and scholar
 * He began the modern discovery of atoms
 * He transformed Democritus’s ideas into a theory
 * He studied ratios of chemical reactions by experimenting
 * ** Dalton’s Atomic Theory ** :
 * 1) ==== All elements are composed of tiny indivisible particles called atoms ====
 * 2) ==== Atoms of the same element are identical. Atoms of one element are different from those of another ====
 * 3) ==== Atoms of different elements can physically combine to form mixtures or chemically combine to form compounds ====
 * 4) ==== Chemical reactions are caused by atoms separating, joining, or rearranging. Atoms of an element are never transformed into atoms of another element ====

Democritus is found below left and Dalton can be seen below right.

=== ===

Lexie page 103
= __**Sizing Up the Atom**__ =
 * A pure piece of copper can be ground into dust
 * A speck of this dust can become smaller
 * When you have reached the smallest possible particle of copper, this is an **ATOM**
 * **Copper atoms are very small**
 * Pure copper in the size of a penny contains 2.4 x 10(22) atoms [the population of earth is about 6 x 10(9) people]
 * If you lined up 100,000,000 copper atoms side by side, the line would be 1cm long
 * The radii of most atoms fall within the range of 5 x 10(-11) m to 2 x 10(-10) m
 * == Despite their small size, individual atoms are observable with instruments such as scanning tunneling microscopes ==
 * [[image:Picture_8.png width="201" height="272"]]
 * a scanning tunneling microscope
 * Individual atoms can be moved around and arranged into patterns
 * This ability holds promise for the creation of atomic-sized electronic devices (such as circuits and computer chips)
 * This atomic-scale ("nanoscale") technology could become essential to future applications in medicine, communications, solar energy, and space exploration

Nick (coeditor) page 104-105
**__Subatomic Particles__**
 * Dalton's theory did not address subatomic particles.
 * Subatomic particles are the particles that make up an atom.
 * The subatomic particles are electrons, neutrons, and protons.[[image:http://images.tutorvista.com/content/feed/tvcs/cathode20rays.gif width="400" height="200" align="right"]]
 * __Electrons__**
 * Electrons are negatively charged.
 * J.J. Thompson discovered the electron in 1897.
 * Thompson did experiments with electrons that involved passing electric currents through gases at low pressures.
 * The gases were in glass tubes that had electrodes(metal disks) on each end.
 * Each electrode was connected to an electrical source.
 * The anode was positively charged and the cathode was negatively charged.
 * A cathode ray was formed between each electrode.
 * Cathode rays could be deflected by electrically charged plates.
 * Positive plates attract the rays and negative plates repel them.
 * This lead to the Thompson saying that the cathode ray was composed of tiny negative particles.
 * These were electrons.
 * Thompson discovered that the ratio of the mass of the electron and charge were the same for all gases.
 * Electrons must be a part of all atoms.
 * Robert A. Milikan continued experimenting on electrons.
 * He measured the quantity of the charge in an electron.

Korey page 106~
= __**Protons and Neutrons:**__ =

[[image:mrdesjardinsdd12wiki/Wiki.jpg width="599" height="191" caption="Properties of Subatomic Particles"]]

 * === **First, atoms have no electric charge; they are electrically neutral.** ===
 * === **One important piece of evidence for electrical neutrality is that you do not receive an electric shock every time you touch something.** ===
 * === Second, electric charges are carried by particles of matter. ===


 * === Third, electric charges always exist in whole-number multiples of a single basic unit; that is, there are no fractions of charges. ===
 * === Fourth, when a given number of negatively charged particles combines with an equal number of positively charged particles, an electrically neutral particle is formed. ===
 * === Considering all of this information, it follows that a particle with one unit of positive charge should remain when a typical hydrogen atom loses an electron. ===
 * === Evidence for such a positively charged particle was found in 1886, when Eugen Goldstein (1850-1930) observed a cathode-ray tube and found rays traveling in the direction opposite to that of the cathode rays. ===
 * === He called these rays canal rays and concluded that they were composed of positive particles. ===
 * === Such positively charged subatomic particles are called protons. Each proton has a mass about 1840 times that of an electron. ===
 * === In 1932, the English physicist James Chadwick (1891-1974) confirmed the existence of yet another subatomic particle: the neutron. ===
 * === Neutrons are subatomic particles with no charge but with a mass nearly equal to that of a proton. ===
 * === Table 4.1 summarizes the properties of these subatomic particles. ===

Kyle S page 106-107

 * __The Atomic Nucleus__ **
 * The discovery of subatomic particles lead many scientists to wonder about the makeup of an atom
 * Some thought electrons were spread out evenly throughout an atom filled uniformly with positively charged material
 * Then came the ground breaking work of Ernest Rutherford

**Rutherford's Gold-Foil Experiment**


 * Rutherford decided that the best thing to do would be to test the current theory about atomic structures
 * In 1911, he conducted an experiment with coworkers at the UNiversity of manchester, England
 * They used a narrow beam of alpha particles and directed it towards a very thin sheet of gold foil
 * Most of these particles passes right through the gold atoms with no deflection, while other bounced off at large angles
 * This went against the theory that said that the particles should have passed through with little deflection

This video should better explain his experiment:

media type="youtube" key="5pZj0u_XMbc" height="315" width="420" align="center"

**The Rutherford Atomic Model**


 * Rutherford created a new theory that the atom was made of mostly empty space, which is why there was very little deflect of the particles
 * This also meant that all of the positive charge and mass that accounted for the large deflection of some of the particle was concentrated in one area in the atom
 * This region would be called the nucleus, which is the small central core of the atom made up of protons and neutrons
 * This model came to be known as the nuclear atom
 * Although it was much improved from previous models, it still was not yet complete

Maddie page 110-111
Atomic Number
 * Atoms are made up of protons, neutrons, and electrons.
 * Protons and neutrons are located in the nucleus
 * Electrons surround the nucleus
 * Elements are different because they contain different numbers of protons
 * The atomic number of an element is the number of protons in the nucleus of an atom of that element.

Mass Number
 * The mass of an atom is concentrated in its nucleus
 * Mass number is the total number of protons and neutrons in an atom.
 * You can calculate the amount of neutrons in an atom
 * The atomic number is equal to the number of protons, which is equal to the number of electrons.
 * The mass number of an element is equal to the number of protons plus the number of neutrons.
 * The number of neutrons in an atom is the difference between the mass number and atomic number.**





= Hannah page 112-114 = = Isotopes = -These element isotopes have different mass numbers -Chemically alike to original element
 * -Isotopes are atoms that have the same number of protons, but different numbers of neutrons.
 * -Hydrogen has 3 isotopes:



= Atomic Mass = -masses of elements are too small to be practical to use -relative masses are compared instead -carbon-12 is used as a standard reference isotope -an atomic mass unit (amu)= 1/12 the mass of a carbon-12 atom
 * -Protons and neutrons have a small mass
 * -Electrons are even smaller in mass
 * -Even large atoms have small masses because the particles that make them up have such small masses
 * -The mass spectrometer is used to find the mass of atoms of elements
 * -Atomic masses are generally not whole numbers

Darby (coeditor) page 115-116
= Atomic Mass (Continued) =

-In nature, most elements occur as a mixture of two or more isotopes

Each isotope of an element has a mixed mass and a natural percent abundance

A weighted average mass of the atoms in a naturally occurring sample of the element

This average reflects both the mass and the relative abundance of the isotopes as they occur in nature

**//__To calculate the atomic mass of an element, multiple the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products__//**

The sum that results if the weighted average mass of the atoms of the element as they occur in nature

__** The Development of Atomic Models **__
-Ernest Rutherford created a model of the atom that explained a few simple properties of atoms. However, his model did not explain the chemical properties of elements. -Certain observations, such as why objects change color when heated, could not be explained with his model. -In order to learn more about the behavior of electrons within atoms, chemists had to develop a new model of the atom that explained these things that were missing. Ernest Rutherford

__**The Bohr Model**__
-Niels Bohr was one of Rutherford's students, who decided to develop a more efficient model of the atom. -He proposed that an electron is found only in specific circular paths or orbits around the nucleus. Neil Bohr (1885-1962)
 * Each electron in his model has a fixed energy. These fixed energy levels that an electron can have are called **energy levels.**
 * A **quantum** of energy is the amount of energy needed to move an electron from one energy level to another.
 * The amount of energy that an electron gains or loses in an atom can change. The higher energy levels are closer together, while lower ones are farther apart. The higher the energy level that is occupied by an electron, the less energy is required to move from that energy level to the next highest energy level.

Watch this video: The Structure of Atoms http://www.youtube.com/watch?v=-YYBCNQnYNM&feature=related

Sean page 128-130
The Quantum Mechanical Model

__ 1926- __ Austrian Physicist Erwin Schrodinger used new theoretical calculations and experimental results to create and solve a mathematical equation that shows the behavior of the electron in a hydrogen atom.

The modern description of the behavior of electrons in atoms that comes from solution to Schrodinger’s equation is called the ** quantum mechanical model. **
 * This model restricts the energy of electrons to certain values but doesn’t include electrons going around the nucleus in an exact path.
 * ** This model determines the allowed energies an electron can have and how easy it is to find an electron in different places around the nucleus. ** How likely it is to find an electron in a particular spot is shown by probability.
 * This model’s description of how electrons move around the nucleus is similar to how a propeller blade rotates in flight. You know the blade is somewhere in the blurry region that you see, but you can’t find its exact location at any moment. Likewise, the quantum mechanical model shows the probability of finding the electron inside of a certain amount of space around the nucleus is represented with a fuzzy cloud. The cloud is less faded where it is more likely to find an electron and is very faded where it is less likely to find one.
 * It is unclear where the cloud stops but it is possible to find an electron very far from the nucleus. So the cloud represents where electrons are found 90% of the time.

Electron Configurations
-change proceeds toward the lowest possible energy -an electron and nucleus interact to make most stable arrangement possible -electron configurations: the ways in which electrons are arranged in various orbitals around the nuclei of atoms

How to find electron configurations of atoms: -states that electrons occupy the orbitals of lowest energy first -orbitals for any sublevel of a principal energy level are always of equal energy -s sublevel is always lowest energy sublevel -range of energy levels within a principal energy level can overlap the energy levels of another principal energy level -states that an atomic orbital may describe at most two electrons -ex.) either one or two electrons can occupy an s orbital or a p orbital -to occupy same orbital: two electrons must have opposite spins  -spin is a quantum mechanical property of electrons (clockwise/counterclockwise)  -a vertical arrow represents an electron and its spin  -one with paired electrons is represented as one arrow up and one arrow down
 * Aufbau Principle
 * Pauli Exclusion Principle

Some elements have an electronic configuration that is an exception to the aufbau principle.

 * ====== This is because half-filled sublevels are not as stable as filled sublevels, but they are more stable than other configurations. ======

These changes occur due to subtle electron-electron interactions within orbitals that have similar energies.

 * ====== Energy differences vetween some sublevels are very small, leading to many exceptions to the aufbau principle. ======

The following video provides an example of exceptions to electron configuration:
[]

Brittany page 138-140
Light:
 * The quantum mechanical model grew out of the study of light
 * Isaac Newton tried to explain what was known about the behavior of light by assuming that light consists of particles
 * However, light actually consists of waves [[image:mrdesjardinsdd12wiki/wavelentgth.jpeg width="213" height="190"]]
 * Each complete wave cycle starts at zero, increases to its highest value, passes through zero to reach its lowest value, and returns to zero again
 * amplitude - the wave's height from 0 to the crest
 * wavelength - distance between crests
 * frequency - number of wave cycles to pass a give point per unit of time
 * usually in cycles per second (hertz)
 * the wavelength and frequency of light are inversely proportional to each other
 * as wavelength increases, frequency decreases
 * as wavelength decreases, frequency increases
 * light consists of electromagnetic waves
 * electromagnetic radiation - includes radio waves, microwaves, infrared waves, visible light, ultraviolet waves, X-rays, and gamma rays
 * all electromagnetic waves travel in a vacuum at 2.998 x 10^8 m/s
 * sunlight consists of light with a continuous range of wavelengths and frequencies
 * when sunlight passes through a prism, the different frequencies separate into a spectrum of colors Calculating Frequency and Wavelength

Atomic Spectra

 * When atoms absorb energy, electrons move into higher energy levels, and these electrons move into higher energy levels, and these electrons lose energy by emitting light when they return to lower energy levels.
 * This light emitted is a specific frequency. Everything has its own frequency of light emitted.
 * The light when put through a prism, is turned into discrete colors which can be viewed as the element’s **Atomic Emission Spectrum**.


 * //__An emission spectrum is like a person’s fingerprint. It is unique to each individual element and no other element has the same one.__//**

=An Explanation of Atomic Spectra=

===
 * The lowest possible energy level for an electron is its **ground state.**
 * When an electron becomes excited by absorbing energy raises it from the ground state into higher levels.
 * Ø When this electron goes back down to a lower level, quanta of energy in the form of light are emitted. This is called an **electronic transition.**
 * The light emitted by an electron moving from a higher to a lower level has a frequency directly proportional to the energy change of the electron.
 * Each transition produces as line of a specific frequency of the spectrum.

===

This is the emission spectrum of a hydrogen atom. There are three groups of lines.
 * The lines at the ultraviolet end of the spectrum are the Lyman series. These are due to the electrons transitioning from higher energy levels to n = 1
 * The lines in the visible spectrum are the Balmer series. The lines result from transitions from higher levels to n = 2
 * Transitions to n = 3 from higher energy levels produce the Paschen series. The energy changes in the electron are generally smaller, so there is less light emitted.
 * Transitions to n = 4, and n =5 also exist; they are not talked about though.
 * Ø There are limits to how high an electron can go because if it gains too much energy it will escape the whole atom.

Ellen page 144-146
Quantum Mechanics -quanta are like particles -light quanta are called photons -led to mathematical expression for wavelength of moving particle -experiments by Clinton Davisson and Lester Germer at Bell Labs in New Jersey proved its validity ~studied bombardment of metals with beams of electrons ~electrons reflecting off metal surface produced patterns like those of X-rays (electromagnetic waves) -De Broglie given Nobel Prize -electrons in electron microscopes have smaller wavelengths than visible light which shows enlarged image of small object -mass of object must be small to see wavelength ~a 50g golf ball at 90 mi/hhas a wavelength of 3*10^-34 but an electron has mass of 9.11*10^-28g at 90 mi/h would be 2*10^-5 -critical when dealing with small particles but with ordinary-sized particles -to locate an electron, you strike electron with photon of light which affects its motion ~measuring position of electron changes the velocity, making the velocity uncertain -leads to concept of electron orbitals and configurations and includes wavelike motion of matter and uncertainty principle This is a diagram of the Heisenberg Uncertainty Principle from the book. And here is a video which explains the Heisenberg Uncertainty Principle: []
 * Einstein explained experimental data by saying light was quanta of energy
 * 1924: Louis de Broglie (French graduate student) asked "Given that light behaves as waves and particles, can particles of matter behave as waves?"
 * Wavelike properties of beams of electrons used in magnifying
 * We can't see effects of wavelike motion in moving objects
 * //__** Classical mechanics describes the motion of bodies much larger than atoms, while quantum mechanics describes the motion of subatomic particles and atoms as waves **__//
 * **Heisenberg uncertainty principle** says it's impossible to know both the velocity and position of a particle at the same time
 * Discovery of matter waves led to Schrodinger's quantum mechanical description of electrons in atoms