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Wonders of the Atom. Within the atom Hang out with the protons, same mass (more or less) not always same numbers of neutrons as protons.

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Presentation on theme: "Wonders of the Atom. Within the atom Hang out with the protons, same mass (more or less) not always same numbers of neutrons as protons."— Presentation transcript:

1 Wonders of the Atom

2 Within the atom Hang out with the protons, same mass (more or less) not always same numbers of neutrons as protons.

3 An Atom’s two regions 1. Nucleus  very small region located near the center of an atom. a)In the nucleus there is at least one positively charged particle called the proton. b)Usually at least one neutral particle called the neutron. 2.Surrounding the nucleus is a region occupied by negatively charged particles called electrons. Nucleons

4 Atoms are different sizes, but they are on the scale of the nucleus (all those protons and neutrons) packed into a pea….Picture that pea sitting in the middle of a stadium The electrons would be whizzing away somewhere in the stands. How Big? Car… still much bigger than a pea!

5 The atom has come along way through history… NamePointsPicture Democritus Different for different elements. Smallest possible “object.” Indivisible. Dalton Spherical. Combine in set ratios. Thomson Positive “pudding.” Negative “plums.” Rutherford Small, dense, positive nucleus. Electron cloud. Divisible. Bohr Electrons orbit nucleus. Electrons have set energy levels. Review

6 Up & Atom Models of Atoms Through the Years. This model of the atom may look familiar to you. This is the Bohr model. In this model, the nucleus is orbited by electrons, which are in different energy levels.

7 What a BohR Electrons Have Specific Energy Levels Bohr’s model aimed to explain spectral lines. When electrons lose energy they emit particular frequencies of light. Bohr showed these particular energies as “orbitals,” similar-looking to the solar system.

8 An electron orbital is a region around an atomic nucleus (not seen) in which one or a pair of electrons is most likely to exist. For each orbital, The red area is where an electron has a positive wavefunction, and the blue area is where the wavefunction is negative. The number and distribution of electrons in an atom's orbitals plays a major role in determining the reactivity and chemical properties of the atom.

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10 Let’s look at a few elements… Hydrogen 1= Proton1= electron

11 Let’s look at a few elements… Helium 2=protons2=neutrons 2=electrons

12 Let’s look at a few elements… Lithium 3=protons4=neutrons 3=electrons

13 Let’s look at a few elements… Fluorine 9=protons10=neutrons 9=electrons

14 Let’s look at a few elements… Argon 18=protons22=neutrons 18=electrons

15 Decay types DecayWhat Happens?How’s the Nucleus? AlphaAn alpha particle emitted from nucleus2 less protons 2 less neutrons Beta (minus) A nucleus emits an electron1 neutron changes to a proton 1 less electron Beta (plus) A nucleus emits an positron1 proton changes to a neutron 1 less electron GammaExcited nucleus releases a high-energy photon (gamma ray) Parts remain the same, but nucleus is less excited NeutronA neutron ejected from nucleus1 less neutron

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17 Energy cannot be created nor destroyed, and energy, in all of its forms, has mass. Mass also cannot be created nor destroyed, and in all of its forms, has energy. Energy and mass are exchangable For example, a water molecule weighs a little less than two free hydrogen atoms and an oxygen atom; the minuscule mass difference is the energy that is needed to split the molecule into three individual atoms (divided by c²), and which was given off as heat when the molecule formed (this heat had mass).

18 In this case the mass difference is the energy/heat that is released when the dynamite explodes, and when this heat escapes, the mass associated with it escapes, only to be deposited in the surroundings which absorb the heat (so that total mass is conserved). Energy and mass are exchangable but this is true only so long as the fragments are cooled and the heat removed…. Likewise, a stick of dynamite in theory weighs a little bit more than the fragments after the explosion.

19 A spring's mass increases whenever it is stretched or compressed. Its added mass is the added potential energy stored within it, which is bound in the stretched electron bonds linking the atoms within the spring. Whenever energy is added to a system, the system gains mass.

20 Raising the temperature of an object (increasing its heat energy) increases its mass. For example, consider the world's primary mass standard for the kilogram, made of platinum/iridium. If its temperature is allowed to change by 1°C, its mass will change by 1.5 pg (1 pg = 1 × 10 −12 g). Whenever energy is added to a system, the system gains mass.

21 A spinning ball will weigh more than a ball that is not spinning. Its increase of mass is exactly the equivalent of the mass of energy of rotation, Which is itself the sum of the kinetic energies of all the moving parts of the ball). For example, the Earth itself is more massive due to its daily rotation, than it would be with no rotation. This rotational energy (2.14 x J) represents 2.38 billion tonnes of added mass. Whenever energy is added to a system, the system gains mass. Note that no net mass or energy is really created or lost in any of these examples and scenarios. Mass/energy simply moves from one place to another.

22 Fission and Fusion Atoms are the building blocks from which matter is formed. Everything around us is made up of atoms. Nuclear energy is contained within the centre of the atom in a place known as the nucleus. Particles within the nucleus are held together by a strong force. If a large nucleus is split apart (fission), generous amounts of energy can be liberated. Small nuclei can also be combined (fusion) with an accompanying release of energy. Using this strong force that holds the nucleus together to produce energy is essentially what the field of nuclear power generation is about.

23 The Power of the sun Fission In The Sun You tube video: HE&feature=related HE&feature=related Reactions: Reactions in Detail: teps.html teps.html Fate of the Sun:

24 Nuclear Power Power Derived from Nuclei wstuffworks.c om/nuclear- power.htm

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26 Control rods They absorb the neutrons Boron is another common neutron absorber. Mechanical properties of boron in its elementary form are unfavourable, therefore alloys or compounds have to be used instead. Cadmium alloys, generally 80% Ag, 15% In, and 5% Cd, are a common control rod material for pressurized water reactors. It has good mechanical strength and can be easily fabricated. It has to be encased in stainless steel to prevent corrosion in hot water.

27 They absorb the neutrons In The Reactor The graphite core slows the neutrons down which increases the likelihood of a collision.

28 Critical mass A critical mass is the smallest amount of fissile material needed for a sustained nuclear chain reaction. The critical mass of a fissionable material depends upon its nuclear properties: its density, its shape, its purity, its temperature and its surroundings.

29 Hydrogen bomb Energy produced by fusion of lighter elements.

30 Bindin g Energy Energy produced by fusion of lighter elements and fission for heavier elements

31 Black Body All matter emits electromagnetic radiation when it has a temperature above absolute zero. The radiation represents a conversion of a body's thermal energy into electromagnetic energy, and is therefore called thermal radiation. It is a spontaneous process of radiative distribution of entropy. Conversely all matter absorbs electromagnetic radiation to some degree. An object that absorbs all radiation falling on it, at all wavelengths, is called a black body. A black body is absorbs all wavelengths of light, and is also the perfect emitter of light. At Earth-ambient temperatures this emission is in the infrared region of the electromagnetic spectrum and is not visible. The object appears black, since it does not reflect or emit any visible light. As the temperature increases past a few hundred degrees Celsius, black bodies start to emit visible wavelengths, appearing red, orange, yellow, white, and blue with increasing temperature. When an object is visually white, it is emitting a substantial fraction as ultraviolet radiation.

32 Black Body Radiation

33 Max Planck Plancking to the max since 1858 (before it was mainstream) Louis de Broglie generalized this relation by postulating that the Planck constant represents the proportionality between the momentum and the quantum wavelength of not just the photon, but any particle. This was confirmed by experiments soon afterwards.

34 Electron volt Is approximately 1.602×10 −19 joule (symbol J ). By definition, it is equal to the amount of kinetic energy gained by a single unbound electron when it accelerates through an electric potential difference of one volt. – Thus it is 1 volt (1 joule per coulomb) multiplied by the electron charge ( ×10 −19 C). Therefore, one electron volt is equal to ×10 −19 J By mass-energy equivalence, the electron volt is also a unit of mass We use this as a much more convenient unit instead of dealing with tiny numbers.

35 Escapist Electrons How do electrons remove themselves from the strong hold of the nucleus? Electrons must do work to escape the nucleus, just as a rocket must do work to escape the gravity of the Earth.

36 Work function is the energy (or work) required to withdraw an electron completely from a metal surface. This is a measure of how tightly a particular metal holds its electrons. The more energy needed to remove an electron, the higher the work function.

37 Functions of different elements Compare Silver and Gold on the periodic table to Calcium and Sodium

38 emission spectra These are the specific frequencies of light that different elements emit. Scientists were puzzled for many years, they decided to focus on trying to explain the “simplest” atom: Hydrogen. Fun Fact: Sodium is used in many street lamps, you can see the emission spectra shows yellows, hence the tell-tale yellow of the street lamp.

39 Hydrogen spectrum Absorption spectra show all the frequencies the element absorbs. Emission spectra show all the frequencies the element emits.

40 Hydrogen spectrum

41 Hydrogen spectrum

42 Hydrogen spectrum

43 Schrödinger's Cat The Cat that Defies Logic what/atoms/quantum/cat.html

44 Bohr He suggested that the interpretation to use depends on what apparatus are used to view the object. Electrons look like particles if probed with photons, but like waves if diffracted through a crystal lattice. Bohr dragged the ideas of matrix mechanics, the Heisenberg uncertainty principle. Towards the end of his career Bohr took a more interpretative role and struggled more and more with the philosophical issues of quantum mechanics First, he came up with the idea of complementarity. He noted that the wave and particle views of an object exclude each other totally but conceded that both are needed in order to fully understand the properties of the object.

45 Experimental results

46 Explanation The photons of a light beam have a characteristic energy determined by the frequency of the light. In the photoemission process, if an electron within some material absorbs the energy of one photon and thus has more energy than the work function, it is ejected. If the photon energy is too low, the electron is unable to escape the material. Increasing the intensity of the light beam increases the number of photons in the light beam, and thus increases the number of electrons excited, but does not increase the energy that each electron possesses. The energy of the emitted electrons does not depend on the intensity of the incoming light, but only on the energy or frequency of the individual photons. It is an interaction between the incident photon and the outermost electron. Electrons can absorb energy from photons when irradiated, but they usually follow an "all or nothing" principle. All of the energy from one photon must be absorbed and used to liberate one electron from atomic binding, or else the energy is re-emitted. If the photon energy is absorbed, some of the energy liberates the electron from the atom, and the rest contributes to the electron's kinetic energy as a free particle. The threshold frequency is typically visible light for alkali metals, near ultraviolet for other metals, and extreme ultraviolet for non-metals.

47 Photoelectric effect The intensity of the light had no effect on the energy of the ejected electrons. Moreover, experiments showed that there was a threshold frequency below, which not a single photoelectron was ejected. Below this frequency, the brightness of the incident light made no difference at all! Classical physics had failed again – it could not explain either of these observations

48 PhotoVoltaic effect In the photoelectric effect, electrons are ejected from a material's surface upon exposure to radiation of sufficient energy. The photovoltaic effect is the creation of a voltage (or a corresponding electric current) in a material upon exposure to light. Though the photovoltaic effect is directly related to the photoelectric effect, the two processes are different.

49 Hydrogen spectrum

50 Different Series Ultraviolet Visible Light Infrared

51 Bohr’s Model

52 Failings While the Bohr model was a major step toward understanding the quantum theory of the atom, it is not in fact a correct description of the nature of electron orbits. Some of the shortcomings of the model are: 1.It fails to provide any understanding of why certain spectral lines are brighter than others. There is no mechanism for the calculation of transition probabilities. 2.The Bohr model treats the electron as if it were a miniature planet, with definite radius and momentum. This is in direct violation of the uncertainty principle which dictates that position and momentum cannot be simultaneously determined. The Bohr model gives us a basic conceptual model of electrons orbits and energies. The precise details of spectra and charge distribution must be left to quantum mechanical calculations, as with the Schrodinger equation.


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