VOCABULARY:

Law of Definite Proportions: The elements composing a compound are always found in the same ratio by mass.

Law of Multiple Proportions: The masses of one element that combine with a fixed amount of another element to form more than one compound are in the ratio of small whole numbers.

Anode: A positive electrode (general); the electrode at which oxidation occurs (electrochemical).

Cathode: A negative electrode (general); the electrode at which reduction occurs (electrochemical).

Cathode Ray: The beam of electrons in a gas discharge tube.

Isotope: One of two or more atoms having the same number of protons but different numbers of neutrons.

Atomic Number: The number of protons in the nucleus of an atom.

Nuclide: An atom of a specific energy with a specified number of protons and a specified number of neutrons in its nucleus.

Nucleon: A particle found in the nucleus of an atom; a proton or neutron.

Mass Number: The total number of protons and neutrons in the atom.

Radioactivity: Spontaneous nuclear decay.

Nuclear Force: The force holding nucleons together in a nucleus.

Subatomic Particle: A particle smaller than an atom.

Lepton: Light subatomic particles.

Hadrons: A class of heavy subatomic particles.

Antiparticle: A particle identical to a second particle in all respects except for opposite charge and magnetic moment.

Neutrino: A neutral particle associated with leptons.

Quark: A theoretical particle believed to be elementary and a constituent of a hadron.

Baryon: A subatomic particle classified as a heavy

Meson: A subatomic particle classified as a hadron.

Gluon: A theoretical mass-less particle exchanged by quarks.

Alpha Particle: A helium nucleus

Beta Particle: An electron (negative) or a positron (positive)

Gamma Ray: A quantum of energy of very high frequency and very short wavelength.

Spectroscopy: The study of the interaction of matter and radiant energy.

Spectrum: A unique set of wavelengths absorbed or emitted by a substance.

Electromagnetic Energy: Radiant energy; energy transferred by electromagnetic waves.

Frequency: The number of complete wave cycles per unit of time.

Hertz: The unit of frequency equal to one cycle per second.

Wavelength: The distance between two successive crests of a wave.

Quantum Theory: A number describing a property of an electron in an atom.

Photon: Quantum of radiant energy.

Ground State: The state of lowest energy of a system.

Atomic Mass: The mass of an atom in atomic mass units; the average mass of the atoms of an element. (Atomic Mass = the number of protons + the number of neutrons).

EARLY ATOMIC THEORY:

• Atoms are so small they cannot be observed directly. Scientists could use only experimental data to help describe the atom.
  
• Around 400 B.C., Democritus (a Greek philosopher) suggested that the world was made of two things - empty space and tiny particles called atoms.
  
• During the 1800's, a French Chemist (Antoine Lavoisier) discovered that chemical "changes" occurring in a closed system - the mass after a chemical change equaled the mass before the chemical change.
  
• He proposed that, in ordinary chemical reactions, matter can be changed in many ways, but it cannot be created or destroyed (Law of Conservation of Mass).
  
• Work by another French Chemist, Joseph Proust, had observed that specific substances always contain elements in the same ratio by _______________ (Law of Definite Proportions).

DALTON'S ATOMIC THEORY:

• Dalton stated a second law based on his own atomic theory but not based on experimental data. It concerns elements that form more than one compound with each other.
  
• For example: Oxygen can combine with Carbon to form Carbon Monoxide, CO, or form Carbon Dioxide, CO₂.
  
• According to Dalton's second law, the ratio of masses of one element that combine with a constant mass of another element can be expressed in __________________________ numbers (or percentages) - This statement is known as the Law of Multiple Proportions.

• Dalton's model of the Atom: Solid Sphere - An indivisible sphere with uniform density and unchanged by a chemical reaction.
• Dalton was the founder of Atomic Theory.

Avogadro, an Italian physicist, stated that equal volumes of gases, under the same conditions, have the ______________________________ of molecules.

ELECTRONS

Experiments by several scientists in the middle 19^th century led to the conclusion that the atom was made up of several smaller particles. With the use of a Cathode-Ray tube it is possible to see these particles.

In each end of the tube there is an electrode. When connected to a source of high voltage electricity, the electrodes become charged.

The positive end is called an _________________. The negative electrode is called the cathode.

Careful observations revealed rays in the tube. Because the rays appeared to begin at the cathode and travel toward the anode, the rays were called cathode-rays.

Cathode ray tubes are in most televisions and computer monitors.

THOMSON'S EXPERIMENTS:

Cathode ray tubes with a fluorescent screen at one end would glow.

Thomson measured the deflection of the beam - Magnet deflected in one direction and plate attracted the beam - therefore, negative particles (electroons).

Deflection of Charged Particles depends on:

• The mass of the particle (large vs. small)
• The ____________________ of the particle (slow vs. fast)
• The electrical charge of the particle (strong vs. weak)
• The strength of the ______________________ (strong vs. weak)
• The amount of charge on the plates (strong vs. weak)

Path of a heavier, more massive particle is bent less than a _________________________ particle.

Calculate the ratio: Charge vs. Mass

• Regardless of the type of gas or metal used in cathode-ray tube - the ratio of charge to mass remained the same. Therefore, the particles in the cathode-ray tube were identical to one another.

Electron, symbol is e^- with a negative one charge.

PROTONS

Thomson also observed in cathode-ray tube, when he used Hydrogen gas and high voltage with low pressure - he noticed that two beams (one negative) and another beam moving in the opposite direction - toward the cathode - a positive beam.

Thomson found that the deflection of the beam varied with different gases. Hydrogen ions had the greatest deflection - therefore the smallest mass.<t;//P>

A Proton is a positively charged particle found in all atoms and each proton possess a plus one charge.

CHARGE AND MASS MEASUREMENTS

Thomson found that electrons were deflected more than protons - therefore an electron must be ________________ massive since the magnitude of charge is equal to each other (electron = negative, proton = positive).

Millikan found the charge on the electron to be 1.602 x 10^-19 coulombs

Mass of the Electron (Thomson) is to be 9.10953 x 10^-28 grams

Since the magnitude of the proton's charge is _______________________ an electrons charge the mass was found to be 1.67265 x 10^-24 grams (1836 times more massive than the electron)

HOMEWORK PROBLEMS:

1a. What evidence showed the the particles in the cathode-ray tube were negatively charged?

1b. Suppose that two beams pass between a pair of oppositely charged plates. One of the beams is composed of electrons, and the other is composed of protons. Will the two beams bend in the same direction or in opposite directions? Why?

1c. What main feature of Dalton's atomic model was abandoned after Thomson's discoveries?

ISOTOPES AND ATOMIC NUMBER

While working with Neon, Thomson observed what seemed to be two kinds of neon atoms. They were exactly alike chemically, but different in their mass. Atoms of the same element that differ in mass are called ___________________. ___________________ have the same number of protons but a different number of neutrons.

The number of ______________________ is known as the atomic number of the element.

The number of protons determines the identity of the element and the number of neutrons determines the particular isotope of the element.

A particular kind of atom containing a definite number of protons and neutrons is called a ____________________. For example, protium, hydrogen-1, is a nuclide of hydrogen.

The total number of protons and neutrons is called the _________________________________ (atomic mass) of that atom.

To find the number of neutrons in an atom: Atomic mass - Atomic number = Number of Neutrons

Unstable Isotopes are __________________________.

RUTHERFORD'S GOLD FOIL EXPERIMENT

Alpha particles (in a beam) are shot at gold, platinum, copper, and tin foil with a fluorescent screen around the sheet of foil and found that:

• Most particles went straight through the foil (supporting the idea that an atom is mostly space).
• Some particles were ___________________________ (supporting the idea that some alpha particles "grazed" the nucleus).
• Some particles were __________________________________ at great angles - back toward the source (supporting the idea that the particles struck the nucleus head on and bounced back).

According to Thomson's Model - the alpha particles should pass through the foil with a few ________________________, but none should have ________________________________ at such a great angle. Since the protons were freely moving through the atom.

Rutherford explained this observation as meaning that there was a very ____________________ to the atom. The core contained all the positive charge and almost all of the mass of the atom. This core is now called the nucleus.

HOMEWORK PROBLEMS:

2a. Make a drawing to illustrate the paths of alpha, beta, and gamma radiation as they pass between two oppositely charged plates. Be sure to label the positive and negative plates.

2b. What unexpected result did Rutherford's gold foil experiment produce?

RUTHERFORD'S ATOM:

Small dense, central core of positive charge - the nucleus has ___________ offf atom's mass.

Electrons move _________________ the nucleus, like bees around a hive.

Rutherford calculated the diameter of the nucleus as _________________________ of the atom's diameter.

Example: Nucleus = Ping Pong Ball, and the Atom's Diameter = 2.0 kilometers.

Rutherford observed that the mass of an atom was ________________________ than the mass predicted from his atomic model (about half the mass). So, he proposed a ___________________ particle in the nucleus that has the same mass as a Proton.

James Chadwick (is credited with the discovery of Neutrons) calculated the energy of ______________________ and inferred its existence since this particle could not be detected or exposed on film.

So Rutherford's model was changed to include ________________________ in the nucleus.

Atoms now contain Protons ( p⁺ ), Neutrons ( n⁰ ), and Electrons ( e^- ). Protons have a positive charge which has the same magnitude charge as Electrons (negative charge), and Neutrons have no charge but has the same mass as a Proton. The ______________________ mass is too small to be considered in the Atom's Mass.

ATOMIC NUMBER AND MASS NUMBER:

Atomic Number is equal to the Number of ______________________.

The number of Protons Identifies an _________________.

If the atom is Neutral (in charge), the number of Electrons equals the number of Protons.

Atoms are ordered on the Periodic Table by increasing ______________________________.

Mass Number: is equal to the ___________________________________ of protons and neutrons in the atom's nucleus.

The average deals with all the Isotopes averaged together.

The Correct way to write an Element's Symbol is with the Mass number on the upper left-hand corner and the Atomic number on the lower left-hand corner with the correct symbol on the right.

If one was to include the charge on an atom, simply place the charge on the upper right-hand corner of the symbol.

*** Let's Determine the number of Protons, Neutrons, and Electrons

HOMEWORK PROBLEMS:

3a. List two ways that a proton differs from an electron.

3b. Which subatomic particle determines a specific element?

3c. What is the mass of an element that contains 20 protons and 22 neutrons?

3d. An atom of sodium contains 11 electrons. What is the atomic number of this atom?

3e. How many neutrons are in the following atoms?

SPECTROSCOPY:

• Frequency equal to the Number of Waves per unit of time. Example: 20 waves in 5 seconds is equal to 4 waves per second.
• The frequency of a wave is the number of waves that pass a point per unit of time.
• Frequency: Symbol is the Greek letter (nu) v.
• Unit of Energy is a Hertz (Hz) = 1/sec or sec^-1
• Wavelength, the distance between similar points in a set of waves (crest to crest or trough to trough).
• Wavelength, the Greek letter (lambda) l
• Amplitude is the distance from the crest (or the trough) from the mid-point of the wave.
• More energy = higher amplitude, high frequency, and short wavelengths.

White light is the combination of colors ranging from red to violet

Red has the _______________________ energy
Long wavelength
Low frequency

Violet has the _______________________ energy
Short wavelength
High frequency

Energy of light depends upon:

• Length of exposure
• Area of exposure
• Frequency of light (high frequency = more energy)

Planck (1900) noticed different types of solids that had different colors - therefore, different frequencies of light, and different energy from atoms.

Planck suggested that _____________________________________, which suggested that the energy of each ________________ was proportional to the frequency of the light wave. (Packets = atoms)

Einstein suggested that packets eventually became known as Photons.

Energy of a Photon = (Planck's Constant) x (frequency) ; h = Planck's Constant = 6.6262 x 10^-34 J-s

Energy values of atoms varied by small whole numbers

Einstein said, "__________________ is proportional with frequency of light"

Light is Quantized Because: (from Quantum mechanics: a branch of physics that describes the behavior of electrons in terms of energy; from the Latin quantus, meaning "how much")

• Each frequency of light has its own energy per photon (specific energies with specific frequencies)
• Einstein suggested that light could be thought of as ______________________ and __________________________.

Quantization in Wave: (Standing Waves)

1 wavelength has 3 nodes (at the Ends and Middle)

1 1/2 wavelength has 4 nodes (at the Ends and 2 in the Middle)

2 wavelengths have 5 nodes …

A ________________ is the location on the wave that has no amplitude.

PRACTICE PROBLEM:

What is the energy of a quantum of light with a frequency of 3.45 x 10¹⁶ Hz?

HOMEWORK PROBLEMS:

4a. What is the frequency of a photon of light that has an energy of 3.68 x 10³³ Joules?

4b. What is the energy of a photon of light that has a frequency of 2.44 x 10¹⁵ Hz?

THE ELECTROMAGNETIC SPECTRUM:

Electromagnetic waves are produced by a combination of ____________________ and ___________________ fields.

All electromagnetic waves travel at the _____________________________ ( 3.00 x 10⁸ meters per second in a vacuum)

The electromagnetic spectrum includes all types of waves:

Frequency increases as ____________________________ Decreases.

Mathematical Relationship:

Speed of light = (wavelength * frequency); Frequency = (speed of light * 1 / wavelength)

Therefore, wavelength and frequency are ______________________ proportional.

PRACTICE PROBLEMS:

1. A certain photon of light has a wavelength of 710 nm. What is the frequency of this light?

2. What is the wavelength of a quantum of light with a frequency of 3.45 x 10¹⁶ Hz?

HOMEWORK PROBLEMS:

5a. What is the wavelength of light with a frequency of 8.55 x 10¹³ Hz?

5b. A certain photon of light has a wavelength of 400 nm. What is the frequency of this light?

5c. A certain photon of light has a wavelength of 3.33 x 10⁸ m. What is the frequency of this light?

BRIGHT-LINE SPECTRUM:

Bright-line spectrum: Distinct (separate) lines of color with distinct frequency which represents an electron gaining energy to go to a higher energy level and returning to its "normal" position.

The energy __________________ is __________________ and converted to Photons (light)

Different amounts of energy - different frequency - different colors of light.

Energy levels: Atoms __________________ specific amounts of energy and then exist for a short time in higher energy levels. Such atoms are described as _______________________.

____________________________ will emit energy as they return to lower energy state.

Bohr's Theory: (used Einstein's idea of Photons of Energy and his calculations for energy of each spectral line, which matched Balmer's Mathematical Relationship.)

Energy Levels: are quantized energy levels that electrons go to and then return to its original energy level.

The levels are NOT like "steps" which are specific distances from the Nucleus. Bohr found that Hydrogen also emitted energy in the Infrared and Ultraviolet Regions thus enhancing his idea of energy absorption and energy release. Bohr used math to predict these occurrences.

HOMEWORK PROBLEMS:

6a. List three examples of waves.

6b. Define: frequency, wavelength, and amplitude of a wave.

6c. What is a photon? What is the difference between a photon of yellow light and a photon of violet light?

6d. How are frequency and wavelength of an electromagnetic wave related?

6e. What wave characteristic determines the energy of a light wave?

WAVE WORKSHEET

QUANTUM WORKSHEET

THE NUCLEUS and RADIATION:

From previous knowledge, you know that chemical changes involve the ______________________ between different atoms in the reactant molecules and the formation of new bonds to form the product molecules.

In a nuclear reaction, changes occur within the ______________________ - involving the ______________________ and ______________________ within the nucleus of a single atom.

Recall that two ______________________ particles reside in the nucleus: the proton and neutron.

Also, recall that atoms of a given element have the ______________________ or protons; this number is known as the ______________________ number.

The atoms of a given element CAN have different numbers of ______________________ and therefore have different mass numbers (the mass number is the total number of protons and neutrons in the nucleus.)

Atoms with the same atomic number but different mass numbers are known as ______________________. The different isotopes of an element are distinguished by citing their ______________________.

For example, there are three naturally occurring isotopes of neon: neon-20, neon-21, and neon-22.

One reason that we must distinguish between different isotopes is that the ______________________ of an atom depend on the number of both protons and neutrons in its nucleus.

In contrast, we already know that an atom's chemical properties are ______________________ by the number of neutrons in the nucleus.

REACTIONS THAT THE NUCLEUS CAN UNDERGO:

A nucleus can undergo a reaction that changes its identity. Some nuclei are unstable and ______________________ emit particles and electromagnetic ______________________.

Such spontaneous emission from the nucleus of the atom is known as ______________________.

Those isotopes that are radioactive are known as ______________________.

An example is uranium-238, which spontaneously emits alpha rays. Recall, that these rays consist of streams of helium-4 nuclei known as alpha particles.

When a uranium-238 nucleus loses an alpha particle, the remaining fragment has an atomic number of 90 and a mass of 234. It is therefore a thorium-234 nucleus.

When a nucleus spontaneously decomposes in this way, it is said to have ______________________, or undergone radioactive decay.

Notice that the mass numbers is the same on both sides of the equation ( 238 = 234 + 4 ). Likewise, the sum of the atomic numbers on both sides is equal ( 92 = 90 + 2 ).

TRANSMUTATIONS:

Another way a nucleus can change identity is to be ______________________ by a neutron or by another nucleus.

Nuclear reactions that are induced in this way are known as nuclear transmutations.

For example, a chlorine-35 nucleus is struck by a neutron ( ); this collision produces a sulfur-35 nucleus and a proton ( or ).

Notice again that the sum of mass numbers and of atomic numbers is the same on both sides of the equation.

By bombarding nuclei with various particles, it is possible to prepare nuclides (an atom with a specific number of protons and neutrons) not found in nature.

HOMEWORK PROBLEMS:

Indicate the number of protons and neutrons in each of the following nuclei:

7a.) carbon-13

7b.) rubidium-85

7c.)

7d.)

7e.) Write a balanced nuclear equation for the nuclear transmutation in which an aluminum-27 nucleus is struck by a helium-4 nucleus, producing a phosphorus-30 nucleus and a neutron.

7f.) Carbon-11, a radioactive nuclide used in medical imaging, is formed by reaction of a proton with nitrogen-14, yielding carbon-11 and helium-4 nucleus (alpha particle). Write the nuclear reaction.

7g) Write a balanced nuclear equation for the nuclear transmutation in which a helium-4 nucleus (alpha particle) strikes a bromine-81 nucleus producing (yielding) a Rubidium-84 nucleus and a neutron.

7h) Fluorine-20 is produced by a reaction of a proton colliding with neon-23, yielding fluorine-20 and a helium-4 nuclei (alpha particle). Write the nuclear reaction.

TYPES OF RADIOACTIVE DECAY:

Emission of radiation is one of the ways in which an ______________________ nucleus is transformed into a ______________________ one with less energy. The emitted radiation is the carrier of the excess energy.

Earlier this year we discussed the three most common types of radiation emitted by radioactive substances: ______________________ ( a ), ______________________ ( b ), and ______________________ ( g ) rays.

Alpha rays consist of streams of ______________________ nuclei known as alpha particles. The below equation show this type of radioactive decay:

Beta rays consist of streams of ______________________. Because the beta particles are electrons, they are represented as . The superscript zero indicates the exceedingly small mass of the electron in comparison to mass of a proton or neutron. The subscript -1 represents the negative charge of the particle, which is opposite of that of a ______________________.

Example: Iodine-131 is an example of an isotope that undergoes decay by beta emission:

Emission of a beta particle has the effect of converting a neutron within the nucleus into a proton, thereby increasing the atomic number of the nucleus by 1:

However, just because an electron is ejected from the nucleus, we need not think that the nucleus is composed of these particles, any more than we consider a match to be composed of sparks simply because it gives them off when struck.

The electron comes into being only when the ______________________ is disruptive.

Gamma rays consist of electromagnetic radiation of ______________________ wavelength (very high energy photons). Gamma rays are represented as . Such radiation neither changes the atomic number nor the mass number of a nucleus.

Two other types of radioactive decay that occur are positron emission and electron capture. A positron is a particle that has the same mass as an electron but an opposite charge. The positron is represented as .

Example: Carbon-11 is an example of an isotope that decays by positron emission:

The positron has a very short life because it is annihilated when it collides with an electron, producing gamma rays:

Emission of a positron can be thought of as converting a proton into a ______________________:

Electron capture is the capture by the nucleus of an inner-shell electron from the electron cloud surrounding the nucleus. Example: Rubidium-81 undergoes decay in this fashion:

Electron capture has the effect of converting a proton within the nucleus into a neutron:

Summary of the Particles Common to Radioactive Decay and Nuclear Transformers:

PARTICLE	SYMBOL
Neutron
Proton	or
Electron
Alpha Particle	or
Beta Particle	or
Positron

HOMEWORK PROBLEMS:

Write balanced equations for the following reactions;

8a.) thorium-230 undergoes alpha decay

8b.) thorium-231 undergoes decay to form protactinium-231.

8c.) Write a balanced nuclear equation for the reaction in which oxygen-15 undergoes positron emission.

Complete and balance the following nuclear equations by supplying the missing particle:

8d.)

8e.)

8f.)

8g.)

HALF-LIFE:

In a sample of radioactive nuclides, the decay of an individual nuclide is a ______________________. It is impossible to predict which nucleus will be the next to undergo a nuclear change.

How, then do you make sense out of things that cannot be predicted on an individual basis? One approach is to predict change for a given amount of a very large ______________________ of nuclei - for example, one half.

Scientists commonly discuss radioactive decay in terms of half-life.

The time it takes for one half of the ______________________ nuclides in a radioactive sample to decay is known as its half-life, or t _1/2.

Example: The half-life of fluorine-21 is approximately ______________________ seconds. If a sample of fluorine-21 contains one-million atoms, then 500,000 of the nuclei will decay within ______________________ seconds.

Within another ______________________ seconds, 250,000 atoms additional nuclei (one-half of those remaining) will decay, and so on.

Many radioactive nuclei have much longer half-lives. A sample of one million nuclei of strontium-90 will decay much more slowly because the half-life of strontium-90 is about ______________________.

Half-lives may be used to calculate the ______________________ of parent nuclides that remain after a certain amount of time.

NUCLEAR REACTIONS FOR ENERGY:

When you look at the stars - (And you SHOULD look at the stars because at one time you where star material! - the atoms that make you up) - you see results of some of the most energetic reactions in the universe.

Earlier you learned that chemical reactions absorb or release energy. Nuclear reactions give off ______________________ times more energy per gram of reactant than chemical reactions.

The light and heat that reach the Earth are the results of nuclear reactions within the sun.

SPLITTING NUCLEI - NUCLEAR FISSION:

Fission is a nuclear reaction in which a nucleus is broken into ______________________ nuclei, often by bombardment with ______________________ of relatively low energy.

Scientists first became aware of fission during their efforts to manufacture transuranium elements (synthesized element, that is one that does not exist in nature) in the 1930's. They discovered that uranium-235 nucleus breaks apart after absorbing a neutron.

The addition of a neutron makes the uranium nucleus unstable. The nucleus splits apart, forming two nuclei - usually with different atomic numbers - and emitting neutrons.

Because the mass of the products is ______________________ than the mass of the reactants, energy is ______________________. The neutrons emitted may be absorbed by other uranium-235 nuclei and cause them to undergo fission, which in turn releases more neutrons and more energy. This self-propagating reaction is called a chain reaction.

By noticing a reduction in mass, once the chain reaction occurred and energy was released - Einstein was able to develop his "famous" equation: E=mc². The equation follows and obeys a law we learned very early in the year - The ______________________: Stating that matter is neither created nor destroyed (it just changes location and form - i.e. energy).

If the amount of uranium-235 is ______________________, many of the neutrons produced by the fission reaction pass through the material without being absorbed. Therefore, as the amount of uranium-235 is increased, the chance for a neutron's striking a nucleus and being absorbed is increased.

The ______________________ amount of material needed to sustain the chain reaction is called the critical mass. The critical mass depends on the number of neutrons produced by each fission and on the concentration and shape of the uranium material.

HOMEWORK PROBLEMS:

9a. Fluorine-21 has a half-life of approximately 5 seconds. What fraction of the original nuclei would remain after 1 minute? If you began with 21 grams of fluorine, how many grams of fluorine would remain? (answer: 0.005 grams)

9b. Iodine-131 has a half-life of 8 days. What fraction of the original sample would remain at the end of 32? (answer: 1/16)

9c. The half-life of chromium-51 is 28 days. If a sample contained 510 grams, how much chromium would remain after 56 days? How much would remain after 1 year? (answer: 130 grams; 0.062 grams)