Chapter 21

Chapter 21:Atomic Structure & interactions : 

Chapter 21:Atomic Structure & interactions By: Ashley Zangla Oslynne Buckner

Internal Structure of the Atom: Key Concepts : 

Internal Structure of the Atom: Key Concepts What is an Atom? Atom- the smallest particle that retains its chemical identity. In 1897, English physicist Joseph John Thomson identified a particle called the electron. Electron- A subatomic particle with negative charge and small mass Thomson’s discovery provided incontrovertible evidence for what some physicists had suspected for a long time: Atoms are not the fundamental building blocks of matter, but they are made up of particles that are smaller and more fundamental still.

Parts of an Atom : 

Parts of an Atom

The Atomic Nucleus : 

The Atomic Nucleus Ernest Rutherford physicist discovered the structure of an atom. o Rutherford used radioactive material, which is matter that sends out energetic particles for his experiment. Scientists called this material that he used alpha particles. § Alpha particles- positively charged particles thousands of times heavier than electrons.

Rutherford’s Experiment : 

Rutherford’s Experiment The experiment was designed to measure something about the way atoms are put together. o With his experiment, Rutherford was going to shoot “bullets” into the atom to see what would happen. § Experiment result: all of the bullets except a few passed straight through the spaces in between the gold atoms, of the gold foil. Some also bounced straight back.

Slide 6: 

What had caused these heavy alpha particles to rebound? Rutherford concluded that a large part of each atom’s mass is located in a very small, compact object at the center, which he called the nucleus. Nucleus- a very small dense, positively charged object at the center of every atom; nuclei are made up of protons and neutrons.

Slide 7: 

For each positively charged electron associated with the atom, there is normally one negatively charged electron associated with the atom. The electric charges of the electrons and the protons are of equal magnitude and so cancel out, therefore atoms are normally electrically neutral. By trying to confirm one model of the atom, Rutherford wound up proposing an entirely different model.

Why the Rutherford Atom Couldn’t Work : 

Why the Rutherford Atom Couldn’t Work If an atom really fit the Rutherford model, the electrons moving in their atomic orbits would constantly give off energy in the form of electromagnetic radiation. The energy would then spiral out toward the nucleus.

The Bohr Atom : 

The Bohr Atom · Niels Bohr produced the first model of the atom that avoided the kinds of objections encountered by Rutherford’s model. Bohr wondered what the results would be if the angular momentum of electrons circling the nucleus came in discrete units. If the angular momentum had a certain discrete bundles, quanta, then there were only certain “allowed energy levels.”

The Ground State and Excited State : 

The Ground State and Excited State · An electron in the lowest energy level is said to be in the ground state. · All energy levels above the ground state are called excited state

Spectroscopy : 

Spectroscopy When energy is added to a system with many atoms in it, electrons in some atoms jump to exited states also when that happens it gives out photons and if some are in the range of light, they appeared to glow. Ex.1 The mercury gas inside a light bulb that passes when a electric current passes through the gas electrons moved up a exited state. Ex 2 Streetlights often used at freeway interchanges, use bulbs filled with sodium atoms and if the sodium is exited, the most frequently photons are emitted that’s is why lamps look yellow.

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Electrons energy levels depend on the electrical attraction between the nucleus and electrons. Different nucleus have different number of protons, so electrons circling them are in different levels. The energies between allowed energy levels within atoms, are different in each of the hundred or so different chemical elements. The total collection of photons emitted by a given atom is called a spectrum. Each possible quantum jump corresponds to light at a specific wavelength so each type of atom produces a different set of lines as shown in figure (21-7)

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3 Examples of how wavelengths work. If the white light shines through a material containing a particular kind of atom, then certain wavelength of light are absorbed. When you absorbed the light on the other side of the material, then certain lines of color are missing. The dark areas corresponding to the absorption lines and they are as much an atom fingerprint as the set of colors that glowing emits. Spectroscopy is used by many astronomers, they use the emission spectra to determine the chemical composition of distance stars.distance stars

The Bohr atom and Spectroscopy : 

The Bohr atom and Spectroscopy In 1905 Albert Einstein propose that light itself consisted of quanta which he called photons. In 1913 Niles Bohr said that the very nature of atoms require quanta of energy and angular momentum. In 1885 a Swiss schoolteacher named Johann Balmer found a formula by trial and error that fit the wavelengths of the most prominent series of lines in hydrogen. In 1890, a Swedish spectroscopist Johannes Rydber’s found a formula that fit all of the other discoveries made by other scientist. His idea was to plug in simple integers such as 1,2 and 3.

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Rydberg formula involve multiplying by a constant with a value of 1.097x 10 ^7. Many scientist had the same formulas that had to be multiply by a constant, but this time it involve the speed of light, the mass and charge of an electron. His formula was 1.097x10^7 which won novel prize in 1992.l prize in 1992.

Spectra of life’s Chemical Reactions : 

Spectra of life’s Chemical Reactions In early 1940s use spectroscopy to see hoe large molecules called enzymes govern chemical reaction in living cells . A fluid containing the material undergoing chemical reactions was allowed to flow down the tube and as the fluid moves further the reaction progressed closer and closer to completion.

The Story of Helium : 

The Story of Helium Helium comes from the word “helios,” whish meant sun in Greek, because it was first discovered by identifying a new set of spectral lines in light from the sun, discover in 1868 by Joseph Norman Lockyer’s. After thrifty years scientist accepted that there was helium on the sun but not earth.but n

The Laser : 

The Laser

Slide 21: 

The action of a laser. Electrons in the laser’s atoms are continuously pumped into an exited state by an outside energy source, and the beam of coherent photons is released when the electrons return to their ground state. As shown In figure (21-9). The mirror from where the beam reflects is designed to be practically reflective 95% of the atoms that hit the mirror are reflected back into the laser. The remaining 5% of photons that leak out form the familiar laser beam. One example of how people use lasers: Ex 1 Scanners in supermarkets.

Periodic Table of Elements : 

Periodic Table of Elements Dmitri Mendeleev, A Russian scientist developed the periodic table in the 19th Century Systematizes all known chemical elements, provides the framework for understanding the structure and interaction of atoms

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The periodic table organized 63 elements when it was first written down by Mendeleev. In the original table there were holes, places where he predicted elements should go

Periodic Chemical Properties : 

Periodic Chemical Properties In any given column, the elements are very similar. Far left column: Alkali Metals: Lithium, Sodium, Potassium etc. Second column: Alkaline earths: Beryllium, Magnesium, calcium etc. Far right column: Noble gases: Helium, Neon, Argon etc.

Atomic Number : 

Atomic Number The Atomic number corresponds to the number of protons in the atom, or, equivalently. If the atom is not charge, to the number of electrons surrounding the nucleus

Why the periodic table works:Electron Shells : 

Why the periodic table works:Electron Shells The pattern of elements in the periodic table mirrors the spatial arrangement of electrons around the atom’s nucleus -The electrons are arranged into shells When two atoms come near enough to one another to undergo a chemical reaction electrons in the outermost shells meet one another first - such as a carbon atom and a oxygen atom in a burning piece of coal

Understanding the Periodic Table : 

Understanding the Periodic Table These outermost electrons govern the chemical properties of materials The behaviors of these electrons must be documented in order to understand the periodic table

Pauli Exclusion Principle : 

Pauli Exclusion Principle No two electrons in an atom can occupy the same state at the same time -once an electron fills a particular space in the atom no other electron can occupy the same space

Electron Shell : 

Electron Shell There are only two spaces that an electron can fill in the inner most electron shell - corresponds to the lowest Bohr energy level - also corresponds to a situation in which the electron spins clockwise on its axis. The other to a situation in which it spins counter clockwise

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Hydrogen with a single electron in the innermost shell, and helium with two electrons in that same shell. If we want to add one more electron, it has to go into the second electron shell because the first electron shell is completely full. - explains why only hydrogen and helium appear in the first row of the the periodic table

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The second electron shell has room for eight electrons, a fact reflected in the eight elements of the periodic table’s second row - Neon appear directly under helium, and we expect these two element to have similar chemical properties because both have a completely full outer electron shell

Predicting Chemical Formulas : 

Predicting Chemical Formulas The periodic table tells you how many electrons are in the outer shell of each element. Atoms are usually more stable with a completely filled outer shell of electrons Elements at the left in the periodic table usually donate electrons -atoms with 7 electrons in the outershell form compounds with elements in a 1-to-1 ratio

For more infromation about what we have discussed : 

For more infromation about what we have discussed - The Ruthford Model http://www.youtube.com/watch?v=FfY4R5mkMY8&feature=related -The bohr Model http://www.youtube.com/watch?v=hpKhjKrBn9s&annotation_id=annotation_736168&feature=iv -Spectra http://www.youtube.com/watch?v=5z2ZfYVzefs&feature=related

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Proton, Nuetrons, & Electrons http://www.youtube.com/watch?v=-P4N-0Wbtyk&feature=related

THANKS 4 YOUR ATTENTION!!!! : 

THANKS 4 YOUR ATTENTION!!!!