(2) Electromagnetic Radiation and Atomic spectra

Three

________ subatomic particles make up atoms

E / 0.00054858 amu / -1

P / 1.0073 / +1

N / 1.0087 / 0

Provide the mass and charge of each particle

• Electron

• Proton

• Neutron

Humphrey Davy

• the compounds decomposed into elements.

• compounds are held together by electrical forces.

_________________ in the early 1800’s passed electricity through compounds and noted and concluded that (2)

Michael Faraday

________________in 1832-1833 realized that the amount of reaction that occurs during electrolysis is proportional to the electrical current passed through the compound

• Consist of 2 electrodes sealed in glass tube containing a gat at very low pressure

• When a voltage is applied to the cathodes a glow discharge is emitted

What are the Cathode ray tubes performed in the late 1800’s and early 1900’s (2)

Cathode Ray Tubes

These are referred to as “rays” that are emitted from cathode (-end) and anode (+end)

Negatively charged

Cathode rays mus be _____________ charged

JJ Thompson

_____________________________ this person modified the cathode rat tube experiments in 1987 by adding two adjustable voltage electrode

Additional electric field

Jj Thompson’s modified cathode ray tube studied the amount that the cathode ray beam was deflected by __________________

charge to mass ratio (e/m) = -1.75882×10^8 coloumb/g

Thomson used his modification yo measure the ____________ of electrons

Thompson'; Electrons

_____________named the cathode rays ________ and is said to be the discoverer of the _______

Robert A. Milkan

__________________ won the Nobel Proze in 1923 for his famous Oil-drop experiment

• e/m = -1.75882×10^8 coloumb/g

• e=-1.60218 × 10^ -19 coloumb

• m=9.10940×10^-28 g

In 1909 Milikan determined the charge and mass of electron which are

(3)

Eugene Goldstein

• opposite

• Canal Rays

__________________noted streams of positively charged particles in cathode rays in 1886.

• Particles move in __________ direction of cathode rays.

• Called “__________” because they passed through holes (channels or canals) drilled through the negative electrode.

• positive

• Canal rays must be _________.

• Goldstein; proton

• ______________ postulated the existence of a positive fundamental particle called the “________”.

Ernest Rutherford

• α-particle

• atom’s structure.

___________ directed Hans Geiger and Ernst Marsden’s experiment in 1910.

• _________ scattering from thin Au foils

• Gave us the basic picture of the ___________

• The atom is mostly empty space.

• It contains a very small, dense center called the nucleus.

• Nearly all of the atom’s mass is in the nucleus.

• The nuclear diameter is 1/10,000 to 1/100,000 times less than atom’s radius.

What are Rutherford’s major conclusions from the α-particle scattering experiment (4)

James Chadwick; Be films

_____________ in 1932 analyzed the results of α-particle scattering on thin __________________

neutrons

Chadwick recognized existence of massive neutral particles which he called _________

atomic number

The ____________ is equal to the number of protons in the nucleus.

• Sometimes given the symbol Z.

• On the periodic table Z is the uppermost number in each element’s box

H.G.J. Moseley

In 1913, _______________________ realized that the atomic number determines the element

• protons

• The elements differ from each other by the number of __________ in the nucleus.

electrons

• The number of ________ in a neutral atom is also equal to the atomic number.

λ

• The wavelength of electromagnetic radiation has the symbol ______.

Wavelength

• 1 Å = 1 x 10-10 m = 1 x 10-8 cm

• ________ is the distance from the top (crest) of one wave to the top of the next wave.

• Measured in units of distance such as m, cm, Å.

• 1 Å = _________ m = ________ cm

V

The frequency of electromagnetic radiation has the symbol v

Frequency

________ is the number of crests or troughs that pass a given point per second.

• Measured in units of 1/time, s-1

velocity = λv.

The relationship between wavelength and frequency for any wave is _____________

2.998 x 10^8 m/s

• c = λv

For electromagnetic radiation, the velocity is ______________ and has the symbol c.

• c = _____ for electromagnetic radiation

Max Planck

• energy is quantized

• light has particle character

In 1900, _____________ studied black body radiation and realized that to explain the energy spectrum he had to assume that: (2)

Planck’s equation

• photoelectric effect

• particle-like behavior

• 1921

Albert Einstein explained the ____________.

Explanation involved light having _______________.

Einstein won the _____ Nobel Prize in Physics for this work.

electron to be ejected

Light can strike the surface of some metals causing an __________________________.

emission spectrum

bright line spectrum

An _____________ is formed by an electric current passing through a gas in a vacuum tube (at very low pressure) which causes the gas to emit light.

▪ Sometimes called a __________________

absorption spectrum

An _____________ is formed by shining a beam of white light through a sample of gas.

wavelengths of light

Absorption spectra indicate the ________________ that have been absorbed.

spectrum

Every element has a unique ______.

Thus, we can use ______ to identify elements.

This can be done in the lab, stars, fireworks, etc.

Rydberg equation

The _______________ is an empirical equation that relates the wavelengths of the lines in the hydrogen spectrum.

Rydberg equation Formula

• Where the electron can be with respect to the nucleus.

• How stable the electron would be in that orbit

From mathematical equations describing the orbits for the hydrogen atom, together with the assumption of quantization of energy, Bohr, was able to determine two significant aspects of each allowed orbit: (2)

• Visible light

• wavelengths

• logarithmic scale

• expanded scale

• increases

___________ is only a very small portion of the electromagnetic spectrum. Most electromagnetic radiation has longer or shorter ___________ than our eyes can detect. The approximate ranges of the electromagnetic spectrum are shown on a _____________. The visible region is shown on an _____________. Note that wavelength ___________ as frequency decreases.

• Atomic emission

• wavelengths

• emission spectrum

• only one excited state at a time

• light emitted

______________. The light emitted by a sample of excited hydrogen atoms (or any other element) can be passed through a prism and separated into discrete __________. Thus, an _____________, which is a photographic recording of the separated wavelengths, is called a line spectrum. Any sample of reasonable size contains an enormous number of atoms. Although a single atom can be in _____________________, the collection of atoms contains many possible excited states. The _________________ as these atoms fall to lower energy states is responsible for the spectrum.

• Atomic absorption.

• white light

• photographic negative

____________\\. When __________________ is passed through unexcited hydrogen and then through a slit and a prism, the transmitted light is lacking in intensity at the same wavelengths as are emitted in part (a). The recorded absorption spectrum is also a line spectrum and the _____________ of the emission spectrum.