The Atom and also Electromagnetic Radiation




You are watching: Most of the mass of an atom is found in its

Fundamental Subatomic Particles Electromagnetic Radiation
Light and also Other develops of Electromagnetic Radiation

Particle Symbol Charge Mass
electron e- -1 0.0005486 amu
proton p+ +1 1.007276 amu
neutron no 0 1.008665 amu

The variety of protons, neutrons, and electrons in one atom have the right to be identified from a set of basic rules.

The variety of protons in the nucleus of the atom is same to the atom number (Z). The variety of electrons in a neutral atom is same to the variety of protons. The mass number of the atom (M) is equal to the amount of the variety of protons and neutrons in the nucleus. The variety of neutrons is equal to the difference between the mass number of the atom (M) and also the atomic number (Z).

Examples: Let"s determine the number of protons, neutrons, and electrons in the following isotopes.


12C 13C 14C 14N

The different isotopes of an element are established by creating the mass variety of the atom in the top left edge of the symbol because that the element. 12C, 13C, and 14C room isotopes the carbon (Z = 6) and also therefore contain six protons. If the atoms are neutral, they likewise must contain six electrons. The just difference between these isotope is the variety of neutrons in the nucleus.

12C: 6 electrons, 6 protons, and also 6 neutrons

13C: 6 electrons, 6 protons, and 7 neutrons

14C: 6 electrons, 6 protons, and 8 neutrons


Practice problem 1:

Calculate the variety of electrons in the Cl- and also Fe3+ ions.

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Electromagnetic Radiation

Much that what is known about the structure of the electrons in an atom has actually been acquired by researching the interaction between matter and also different develops of electromagnetic radiation. Electromagnetic radiation has actually some that the properties of both a particle and a wave.

Particles have a definite mass and also they occupy space. Waves have actually no mass and also yet they carry energy as they travel with space. In enhancement to their ability to bring energy, tide have four other characteristic properties: speed, frequency, wavelength, and also amplitude. The frequency (v) is the variety of waves (or cycles) per unit that time. The frequency that a wave is reported in devices of cycles per second (s-1) or hertz (Hz).

The idealized drawing of a tide in the figure below illustrates the interpretations of amplitude and wavelength. The wavelength (l) is the smallest distance between repeating point out on the wave. The amplitude the the wave is the distance between the highest (or lowest) point on the wave and also the facility of gravity of the wave.

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If us measure the frequency (v) the a wave in cycles per 2nd and the wavelength (l) in meters, the product the these two numbers has actually the units of meters every second. The product of the frequency (v) times the wavelength (l) the a wave is thus the speed (s) at which the tide travels v space.

vl = s


Practice problem 2:

What is the rate of a tide that has actually a wavelength that 1 meter and a frequency the 60 cycles per second?

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Practice difficulty 3:

Orchestras in the United says tune their instruments to an "A" that has a frequency the 440 cycles per second, or 440 Hz. If the speed of sound is 1116 feet every second, what is the wavelength that this note?

Click right here to check your answer come Practice difficulty 3

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Light and Other develops of Electromagnetic Radiation

Light is a wave through both electric and also magnetic components. It is therefore a kind of electromagnetic radiation.

Visible light contains the narrow band that frequencies and also wavelengths in the portion of the electro-magnetic spectrum the our eyes deserve to detect. It includes radiation v wavelengths between about 400 nm (violet) and 700 nm (red). Since it is a wave, irradiate is bent as soon as it beginning a glass prism. Once white irradiate is concentrated on a prism, the light rays of various wavelengths space bent by differing amounts and the light is transformed into a spectrum that colors. Starting from the next of the spectrum where the light is bending by the smallest angle, the colors room red, orange, yellow, green, blue, and violet.

As we have the right to see from the following diagram, the energy brought by light increases as we go native red come blue across the clearly shows spectrum.

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Because the wavelength the electromagnetic radiation have the right to be as long as 40 m or as brief as 10-5 nm, the visible spectrum is only a small section of the total selection of electromagnetic radiation.

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The electromagnetic spectrum includes radio and also TV waves, microwaves, infrared, visible light, ultraviolet, x-rays, g-rays, and cosmic rays, as shown in the number above. These various forms of radiation all take trip at the rate of light (c). Lock differ, however, in your frequencies and wavelengths. The product the the frequency time the wavelength the electromagnetic radiation is constantly equal come the speed of light.

vl = c

As a result, electromagnetic radiation that has actually a lengthy wavelength has actually a low frequency, and also radiation with a high frequency has actually a quick wavelength.


Practice difficulty 4:

Calculate the frequency of red light that has a wavelength that 700.0 nm if the speed of light is 2.998 x 108 m/s.