Elucidation of the structure of the periodic table The number of electron shells an atom determines the atomic period. Each skin has a subshell, which is loaded according to the following sequence, along with increasing atomic number: 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 8s 5g 6f 7d 7P 8p
Minggu, 06 Mei 2012
MID TEST
BASIC CHEMISTRY
LECTURE:Dr.Syamsurizal
1.Explain where is the key point of the similarities and diffrences between matter waves and electromagnetic waves.Give at least two examples.
2.Do atoms in excited states emit radiation randomly, at any wavelength?why? what does it mean to say that the hydrogen atom has only certain discrete energy levels available?how do we know this?why was the quantization of energy levels suprising to scientists when it was first discovered?
3.You have much studied some things related to the modern atomic theory.Do you think electrons are more like baseballs or guitar strings.explain your reason.
4.Describe the relationship between stability and potential energy.give at least two examples.
5.You have carried out an experiment about the water surface tension properties in the paper,plastic,and glass.write down your observations.comparing the cohesive and adhesive forces on all three materials,why is that?
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1.Electromagnetic waves are very much different from the matter waves and in many ways.
BalasHapusa) Speed of matter waves is very much less than the speed of electromagnetic waves.
b) Matter waves cannot be radiated in empty space unlike electromagnetic waves.
c) Matter waves are just associated with the particle, not emitted by it
Matter waves have smaller wave lengths than electromagnetic waves
example of matter waves:- photo-electrons
- ballistic electrons in nanotechnology devices (scanning-tunneling microscopy, quantum Hall effect)
- atoms released from a coherent source (atom laser).
example of electomagnetic waves: Radio-waves
Infra-red
Microwaves
Ultra-violet radiation
visible light
X-rays
2.some atoms, the ones that are radioactive, have a nucleus that is unstable, and it will "break apart" at some time. The protons and neutrons that are fused in a given nucleus of a given isotope of a given element might not, for some reason, like the arrangement they are forced to accept when the nucleus is made. As a result, that nucleus is unstable and likely to decay by some mechanism. When an atom of a radioactive isotope decays, it emits radiation (particulate and/or electromagnetic) as a way to loose energy to shift to a more "acceptable" nuclear state.
Note that the more "acceptable" nuclear state may, itself, be another radioactive isotope, and it will decay sooner or later to form yet another nucleus. This will continue over time until that atom reaches a stable nuclear state. Further decay will not occur as the protons and neutrons in the nucleus are now "happy" with the way things are and will stay together.
"Discrete", in this sense, means the opposite of "continuous". An example of a continious variable would be the speed of a car. It can be anywhere between 0 and its maximum speed. A discrete variable, on the other hand, would be the gear the car is in. It can be park, reverse, neutral, or drive, but not between any of those gears.
So for a hydrogen atom, what this means is that its energy level can be one of a distinct number of levels. It can't be between two of those levels.
3.electrons could act as both particles and waves. De Broglie's hypothesis was soon confirmed in experiments that showed electron beams could be diffracted or bent as they passed through a slit much like light could. So, the waves produced by an electron confined in its orbit about the nucleus sets up a standing wave of specific wavelength, energy and frequency (i.e., Bohr's energy levels) much like a guitar string sets up a standing wave when plucked.The diagram above illustrates an electron standing wave vibrating in an orbit around a nucleus of an atom. Only integral numbers of wavelengths are allowed. Below is a series of diagrams that illustrate the allowed vibrations of a string fixed on both ends. If a string is fixed on both ends, then the only waves that can occur are those with zero amplitude at those fixed ends; such points of zero amplitude are called nodes. Below we show four of the infinite number of vibrations with a node at each end. These vibrations are called standing waves.
4.The more potential energy something has, the more unstable it is. Masses (that is to say, stuff that has mass) is better when it's more stable, so it converts the potential energy into, say, kinetic, to make it more stable.
This can be demonstrated with stanidng a stick on it's end, and it falls over, because it's more stable horizontally, because it has less potential energy.
5.when I see the water in plastic, paper, and glass, convex shape of the surface water is kohesive which means the density of water is smaller than the surface of the object.The cohesive forces between molecules are shared with all neighboring atoms.
Since the surface has no neighboring atoms above, they exhibit stronger attractive forces for their neighbors next to and below them