Atomic Structure and You

What is in an atom? What is the difference between protons, neutrons, and electrons? The three main subatomic particles are distinguished by mass, charge, and location in the atom.

What Is in an Atom?, continued Atoms are mostly empty space Comprised to two main parts Nucleus – center portion containing protons and neutrons Electron Cloud – outside orbitals where electrons surround the nucleus

Atomic number The Atomic Number is found in the top corner of each periodic square. Each element has its own Atomic Number - atomic number: the number of protons in the nucleus of an atom. (Z value) The number of Protons identify the atom. Change the atomic number and you have a new element!

Average atomic mass It is the decimal at the bottom of the squares. It represents the average mass of all the atoms that make up this element. It’s like taking the average weight of everybody in class. Not exact, but gives a rough estimate of the weight.

Mass number The mass number equals the total number of subatomic particles in the nucleus. That would be…. ______ + _______ The most common mass number is determined by rounding average atomic mass. HOWEVER IT CAN BE DIFFERENT!!!

Practice! List the Atomic Number for: 1) Copernicium 2) Rutherfordium List the most common Mass Numbers for: 1) Ytterbium 2) Xenon

What about the other particles? We know how to get the number of Protons – Right? Most atoms are neutrally charged. For that to occur the positive charges are canceled out by the negative charges. What does that mean about the total number of Protons and Electrons?

What about the other particles? What does the mass number represent? Where can we always go to get the number of Protons? So if we know the total number of particles in the nucleus, and we know how many protons there are, can we solve for neutrons? # of Neutrons = Mass Number – Atomic Number (Protons)

More practice! How many neutrons would the following atoms have, assuming their most common Mass #? 1) Dubnium 2) Sodium 3) Nitrogen

Isotopes… what are they? Not every atom is exactly the same, different elements have a different number of protons. However even atoms of the same element are not exactly the same, atoms of the same element can have different number of neutrons. These are called Isotopes.

Isotopic Notation Isotopic Notation is generally how isotopes are written. Mass number on top Atomic number on bottom This format makes it easy to calculate number of Neutrons…

Continued… Isotopes have different mass numbers and also different numbers of neutrons. Mass Number – Atomic Number = Neutrons

Practice makes perfect! Identify the number of Protons, Neutrons, and Electrons for each of the following: A) Carbon-12 B) Carbon-14 C) 104Be D) Phosphorus-32

ions Changing the amount of protons in an atom changes the element Changing the amount of neutrons in an atom makes it an isotope Changing the amount of electrons in an atom makes it an ION.  A neutral atom has precisely equal numbers of protons (+) and electrons (–). Atoms with a charge imbalance are called ions. A positive ion has lost one or more electrons (Cation) A negative ion has gained one or more electrons (Anion)

Examples Now let's look at how a positive ion of beryllium is formed. Below, on the left, is a neutral atom of beryllium containing four protons and five neutrons. Circling the nucleus are four electrons. On the right, the atom has lost two electrons. The resulting ion still has four protons in the nucleus but contains only two electrons. There are now two more positive than negative charges; therefore the ion has an overall charge of 2+. (Be2+) Beryllium Atom Beryllium Ion ( Be ) ( Be 2+ )

A negative ion is formed in a similar way A negative ion is formed in a similar way. Below, on the left, is an image of a neutral fluorine atom containing nine protons, nine electrons, and ten neutrons. When fluorine enters into a compound, it picks up an electron from the atom it bonds with. The resulting ion, called a fluoride ion, contains ten electrons and nine protons, with an overall charge of 1- (F1-) Fluorine Atom ( F ) Fluoride Ion ( F1- )

Stable vs unstable isotopes If an isotope is stable, it will stay just as it is. There is no reason for it to change! If an isotope is unstable, it will undergo a nuclear reaction in order to become stable. These are nuclear reactions, not chemical reactions, so there are changes in the nucleus and not the electrons in the cloud. Nuclear reactions produce approximately 500,000 times more energy than chemical reactions.

stable isotopes are nonradioactive; unstable isotopes are radioactive ALL elements 1-82 have stable & unstable isotopes Elements 83 and above have ONLY unstable isotopes and are radioactive. This means they will ALWAYS decay until they reach stable configurations (so they decay to lead, #82, or smaller)

Stability The stability of an isotope depends on the Proton to Neutron ratio – A) A 1:1 ratio of protons and neutrons is stable in lighter elements Ex: C-12 is stable with 6 neutrons and 6 protons B) A 1.5:1 or 3:2 ratio is stable in heavier elements, Ex: Hg-202 is stable with122 neutrons and 80 protons

Types of radioactivity 3 kinds of radioactivity – (natural breakdown of unstable nuclei by giving off particles) 1. Alpha Particles 42a = 42He - equivalent to Helium nuclei (helium without electrons) - not very penetrating (can be stopped by paper) - do not travel very fast (only 1/10 the speed of light) - very large particle (compared with others)

Alpha decay X A Z Y A - 4 Z - 2 + He 4 2

Uses for alpha radiation Smoke Detectors! Americium-241 releases alpha particles into the air around it, creating an electric charge. When smoke gets in the way, the charge stops and the battery inside sends the alarm! Cancer Treatment Radium-223 can be placed directly in the middle of a tumor to kill the cancer cells. Because of the low- penetrating power, alpha particles can’t reach to the healthy cells! Space Craft Heat and Electricity! Plutonium-238 emits alpha particles and a bunch of heat, which keeps the spacecraft warm, and excess heat is turned into electricity to run the craft!

2. Beta Particles 0-1β = 0-1e - can be stopped by aluminum - identical to electron, but still comes from the nucleus - can be stopped by aluminum - very high speed (9/10 the speed of light) - formed when a neutron becomes a proton (advanced particle physics stuff…)

Beta Decay X A Z Y Z+1 + b -1

Uses for beta radiation PET Scans and other Tracers! Short-lived radioactive elements are injected into your vein and allowed to travel through the body during PET Scans. A machine is then used to see where these atoms moved about through your body by detecting the beta particles! Can also be used in machinery or pipe systems to look for leaks or cracks! Cancer Treatment! Strontium-90 is often used to produce a consistent amount of beta particles, which can be directed at a tumor to kill off specific cells! Healthy cells may be damaged as well, but they are better at repairing themselves than cancer cells.

3. Gamma Rays 00γ or γ - not a particle at all so has no element symbol - never emitted on its own, always with alpha or beta - high frequency electromagnetic waves - have no mass but possess energy - most penetrating – stopped only by thick Pb or concrete - move at the speed of light

Uses of gamma radiation Cancer Treatment! Radium and Cobalt are often used to produce a consistent amount of high energy gamma rays. They can either be directed like a knife right at the tumor, or injected into the body where it targets cells that rapidly multiply! Sterilize Equipment Used to sterilize and kill any bacteria or germs from medical equipment and also sterilize packaged foods.

An experiment… Before we knew the composition of the atom, an experiment was conducted by Henri Becquerel and Marie Curie. A radioactive atom was passed through a magnet and three things were recorded. Can you figure out what they were?

Rules for nuclear reactions Two parts to every reaction: Reactants Products Starting materials  Ending materials Means a reaction has happened Laws of Conservation: Certain properties are maintained throughout any reaction, nuclear or chemical - charge - mass and mass numbers

Balancing nunclear equations If we know the starting isotope and the type of decay, we can determine the new isotope that is formed in the process. Ex: 22688Ra  42He + _______ What kind of particle is this? What do you think this is? This is an example of alpha decay because the unstable nucleus has produced an alpha particle

Balancing nuclear reactions If we know the starting and final isotopes, we can also determine the type of radiation that was given off. Ex: 4219K  4220Ca + _______ What kind of particle is this? What kind of decay is this reaction then?

Particles: Alpha: 42He or 42α Beta: 0-1e or 0-1β Proton: 11p or 11H Neutron: 10n Gamma: 00γ or γ

Whats the point of nuclear reactions Trying to reach a STABLE nucleus! (at least to lead, Pb) This often doesn’t happen with one reaction! Let’s take a look at the process at which radium-226 goes through to become stable…

What 2 things are changing with each alpha decay? What 1 thing changes with each beta decay?

Other areas of nuclear chemistry… Nuclear Fission: large atoms break apart into smaller ones Nuclear Fusion: small atoms combine to make larger ones *Both processes release massive amounts of energy!

Fission Fission means “to divide” Nuclear fission is the process of splitting a large nucleus into two nuclei with smaller masses. Additionally, more neutrons are released, as well as large amounts of energy. Only large nuclei with atomic numbers above 90 can undergo fission. The absorption of the neutron causes an instability inside the nucleus. A reaction occurs that produces a lot of energy!

Chain reaction We can block a chain reaction by putting small and stable atoms around the uranium, so that the neutrons are blocked

fission A chain reaction is an ongoing series of fission reactions. Billions of reactions occur each second in a chain reaction. The additional neutrons produced from the previous reaction go on to split new atoms.

Uses of Fission On earth, nuclear fission reactions take place in nuclear reactors, which use controlled chain reactions to generate electricity. Products are Radioactive and must be stored!

fusion - process in which light elements combine to form heavier elements ie: 4 H+  42He + 201e + energy 3H + 2H  42He + 10n + energy Needs extremely high temps to occur, in the millions of degrees Celcius! The hydrogen bomb is a fusion bomb, which gets the temps required by using a fission bomb - Have not been able to beneficially do this on Earth yet. Either it’s destructive, or takes as much energy to start it as we get out of it.

fusion

Nuclear bombs Nuclear Bomb of 1945 known as “fat man” was dropped on the Japanese city of Nagasaki. It along with “little boy” dropped on Hiroshima were the first time nuclear bombs were used in war. Their destruction was nothing like the world had ever seen at the time!

What would that do to marion square?

Red = 100 % building destruction Green = Lethal Radiation dose 90% Blue= Most building collapse Orange = 3rd degree burns to all exposed

Einstein’s equation -Two scientists (Hahn and Strassman) found that the overall mass decreases after a fission reaction occurs. -This is due to what is called the Strong Nuclear Force, which is what helps to hold the nucleus together. By breaking apart the nucleus, some of the this force is no longer needed and goes away.

Einstein’s equation Einstein researched this further and came up with his famous equation E=mc2 which applied to nuclear fission, fusion and radioactive decay (all that alpha, beta, and gamma stuff we just learned!) E=mc2 shows the relationship between mass and energy. C is the speed of light, or 300,000,000 m/s.

Einstein’s Equation E=mc2 C is the speed of light, or 300,000,000 m/s. By squaring C in the equation, even the smallest amount of mass that changes into energy produces HUUUUUGE amounts of energy. FARRR more energy available than ANY regular chemical reaction.

Einstein’s equation Converting 1 kg of Uranium-235 into energy. E = mc2 E = (1kg) * (300,000,000m/s)2 E = 90,000,000,000,000,000 Joules E = 9x1016 joules Energy produced burning 1 kg of coal (not using E = mc2) E = 31,000,000 joules E = 3.1 x 107 joules So: if 1kg of Uranium-235 was converted into energy, it will produce over 1 trillion times the energy of 1kg of coal being burned! Granted, it’s very hard to get this much Uranium to turn into energy all at once, but that’s exactly what happens in our nuclear power plants.

What is half life? Isotope Half-Life Carbon-14 5700 years The half-life of an element is the time it takes for half of the material you started with to decay. Each element has it’s own half-life. Each element decays into a new element - C14 decays into N14 4. The half-life of each element is constant. It’s like a clock keeping perfect time. Now let’s see how we can use half-life to determine the age of a rock, fossil or other artifact. Isotope Half-Life Carbon-14 5700 years Cobalt-60 5.25 years Iodine-131 8.04 days Iron-53 8.9 minutes Phosphorus-32 14.3 days Polonium-210 138 days Radium-226 1620 years Sodium-24 14.9 hours Uranium-238 4.5 billion years

The blue grid below represents a quantity of C14. C14 – blue N14 - red Half lives % C14 %N14 Time elapsed 100% 0% 0 years

After one half life… After 1 half-life (5730 years), 50% of lives % C14 %N14 Time Elapsed 100% 0% 0 years 1 50% 5,730 years After 1 half-life (5730 years), 50% of the C14 has decayed into N14. The ratio of C14 to N14 is 1:1. There are equal amounts of the 2 elements.

After the 2nd half life Now 2 half-lives have gone by for a total % C14 %N14 Time Elapsed 100% 0% 0 years 1 50% 5,730 years 2 25% 75% 11,460 years Now 2 half-lives have gone by for a total of 11,460 years. Half of the C14 that was present at the end of half-life #1 has now decayed to N14. Notice the C:N ratio. It will be useful later.

After the 3rd half life After 3 half-lives (17,190 years) only % C14 %N14 Time Elapsed 100% 0% 0 years 1 50% 5,730 years 2 25% 75% 11,460 years 3 12.5% 87.5% 17,190 years After 3 half-lives (17,190 years) only 12.5% of the original C14 remains. For each half-life period half of the material present decays. And again, notice the ratio, 1:7

What half life looks like in a line graph…

Band of stability If an isotope falls above the band, then it needs to lose neutrons and gain more protons to become stable. How would it achieve that? If an isotope had too many protons and too many neutrons, how would it become stable? Alpha Decay Beta Decay Positron Emission