5.4, 5.5, & 5.6 Flashcards
an atom in its normal state is electrically …………., each electron in an atom must be balanced by the same amount of positive charge.
neutral
(It is the flow of ………….. that produces currents of electricity, whether in lightning bolts or in the wires leading to your lamp.)
electrons
………….. ……….. (…….. particles) are helium atoms that have lost their electrons and thus are positively charged.
Alpha particles / α
The mass of an electron is nearly …………… times smaller than the mass of a proton; the electron carries an amount of charge exactly equal to that of the proton but opposite in sign (Figure 5.15).
Opposite charges attract each other, so it is an electromagnetic force that holds the proton and electron together, just as gravity is the force that keeps planets in orbit around the Sun.
2000
On Earth, a typical atom has the same number of electrons as protons, and these electrons follow complex orbital patterns around the nucleus.
Deep inside stars, however, it is so ………… that the electrons get loose from the nucleus and lead separate yet productive lives.
hot
The ratio of neutrons to protons increases as the number of protons increases, but each element is unique. The number of neutrons is not necessarily the same for all atoms of a given element.
The various types of hydrogen nuclei with different numbers of neutrons are called ………… of hydrogen (Figure 5.17), and all other elements have …………… as well.
isotopes
You can think of isotopes as siblings in the same element “family”—closely related but with different characteristics and behaviors.
Bohr further assumed that as long as the electron moves in only one of these allowed orbits, it radiates no energy: its energy would change only if it moved from one ………. to another.
orbit
But at the microscopic level of the atom, experiment after experiment has confirmed the validity of Bohr’s strange idea. Bohr’s suggestions became one of the foundations of the new (and much more sophisticated) model of the subatomic world called …………. ………….
quantum mechanics
In Bohr’s model, if the electron moves from one orbit to another closer to the atomic nucleus, it must ……… …… some energy in the form of electromagnetic radiation.
If the electron goes from an inner orbit to one farther from the nucleus, however, it requires some ……….. ………
give up
additional energy
One way to obtain the necessary energy is to absorb electromagnetic radiation that may be streaming past the atom from an outside source.
A key feature of Bohr’s model is that each of the permitted electron orbits around a given atom has a certain energy value; we therefore can think of each orbit as an ………… …………… To move from one orbit to another (which will have its own specific energy value) requires a change in the electron’s energy—a change determined by the difference between the two energy values.
energy level
Here we have one of the situations where it is easier to think of electromagnetic radiation as particles (…………….) rather than as waves. As electrons move from one level to another, they give off or absorb little packets of energy. When an electron moves to a higher level, it absorbs a …………. of just the right energy (provided one is available). When it moves to a lower level, it emits a …………n with the exact amount of energy it no longer needs in its “lower-cost living situation.”
photons
The photon and wave perspectives must be equivalent: light is light, no matter how we look at it. Thus, each photon carries a certain amount of energy that is proportional to the frequency (f) of the wave it represents. The value of its energy (E) is given by the formula ……………………….
value h = ………….. joule-seconds (J-s).
6.626 × 10–34
We can use Bohr’s model of the atom to understand how spectral lines are formed. The concept of energy levels for the electron orbits in an atom leads naturally to an explanation of why atoms absorb or emit only specific energies or wavelengths of light.
R 1
each type of atom has its own unique pattern of electron orbits, and no two sets of orbits are exactly alike. This means that each type of atom shows its own unique set of spectral lines, produced by electrons moving between its unique set of orbits.
R 3
Ordinarily, an atom is in the state of lowest possible energy, its ………. ……….
In the Bohr model of the hydrogen atom, the ………. ………. corresponds to the electron being in the innermost orbit.
ground state / ground state
An atom can absorb energy, which raises it to a higher energy level (corresponding, in the simple Bohr picture, to an electron’s movement to a larger orbit)—this is referred to as ………….
The atom is then said to be in an ………… ………..
excitation
excited state
Generally, an atom remains excited for only a very …….. ……….. Then it goes back to the ground state either by one jump or gradual jumps
brief time
When we measure the energies involved as the atom jumps between levels, we find that the transitions to or from the ground state, called the ………… ………. of lines, result in the emission or absorption of ……………. photons.
Lyman series / ultraviolet
the transitions to or from the first excited state called the ………… ……….., produce emission or absorption in …………. light.
Balmer series / visible
Atoms that have absorbed specific photons from a passing beam of white light and have thus become excited generally de-excite themselves and emit that light again in a very short time. You might wonder, then, why dark spectral lines are ever produced. In other words, why doesn’t this reemitted light quickly “fill in” the darker absorption lines?
Some of the reemitted light is actually returned to the beam of white light you see, but this fills in the absorption lines only to a slight extent. The reason is that the atoms in the gas reemit light in all directions, and only a small fraction of the reemitted light is in the direction of the original beam (toward you).
If enough energy is absorbed, the electron can be completely removed from the atom—this is called …………….
The atom is then said to be ……………
The minimum amount of energy required to remove one electron from an atom in its ground state is called its …………… …………..
ionization. / ionized / ionization energy.
after the first, Successively greater energies are needed to remove the third, fourth, fifth—and so on—electrons from the atom.
When we examine regions of the cosmos where there is a great deal of energetic radiation, such as the neighborhoods where hot young stars have recently formed, we see a lot of ionization going on.
From a knowledge of the temperature and density of a gas, it is possible to calculate the fraction of atoms that have been ionized once, twice, and so on.
In the Sun, for example, we find that most of the hydrogen and helium atoms in its atmosphere are ………………., whereas most of the calcium atoms, as well as many other heavier atoms, are ……….. ………….
neutral
ionized once
He pointed out that if a light source is approaching or receding from the observer, the light waves will be, respectively, …………. more closely together or ………… …………..
The general principle, now known as the …………. …………
crowded / spread out
Doppler effect
We can see from this illustration that the Doppler effect is produced only by a motion ………… or …………. from the observer, a motion called ………… …………..
……………….. motion does not produce such an effect.
toward or away
radial velocity
Sideways
As wavelength decreases, they shift toward the blue end of the spectrum: astronomers call this a ………………
When the source moves away from you and the wavelength gets longer, we call the change in colors a …………..
- blueshift*
- (since the end of the spectrum is really violet, the term should probably be* violetshift**, but blue is a more common color)
- redshift*
