Chemistry Chapter 5.1 Models of the Atom

The second principal energy level (n=2) has ___ sublevels, 2s and 2p. The 2s orbital is ___-shaped and the 2p orbitals are ___-shaped.

2; spherical; dumbbell

Although it is unclear where the cloud ends, there is at least a slight chance of finding the electron a considerable distance from the nucleus. Therefore, attempts to show probabilities as a fuzzy cloud are usually limited to the volume in which the electron is found ___% of the time.

90

Give an example of probability.

If you place 3 red marbles and one green marble into a box and then pick a marble without looking, the probability of picking the green marble is one in four, or 25%. This means that if you tried putting the four marbles in a box and picking one, and repeated this a great many times. you would pick a green marble in about 25% of your tries.

Describe a visualization of an electron probability cloud.

Imagine you could mold a sack around the cloud so that the electron was inside the sack 90% of the time. The shape of the sack would then give you a useful picture of the shape of the cloud.

What is the quantum mechanical model?

In 1926, Austrian physicist Erwin Schrodinger (1887-1961) used these new results to obtain and solve a mathematical equation describing the behavior of the electron in a hydrogen atom. This modern description of the electrons in atoms, the quantum mechanical model, comes from the mathematical solutions to the Schrodinger equation.

Like the Bohr model, the quantum mechanical model of the atom restricts the energy of electrons to certain values. But how does the quantum mechanical model differ from the Bohr model?

In a radical departure from the Bohr model, the QMM does not involve an exact path the electron takes around the nucleus. The QMM determines the allowed energies an electron can have and how likely it is to find the electron in various locations.

The amount of energy an electron gains or loses in an atom is not always the same. Explain.

Like the rungs of a strange ladder in which the rungs aren't spaced evenly, the energy levels in an atom aren't spaced evenly. The higher energy levels are closer together. It takes less energy to climb up one rung near the top of the ladder where the rungs are closer, just as the higher the energy level occupied by an electron, the less energy it takes to move from one energy level to the next energy level.

What is the Bohr model?

Niels Bohr (1885-1962), a young Danish physicist & student of Rutherford's, believed Rutherford's model needed improvement. In 1913 Bohr changed R'sM to include newer discoveries about how atoms change energy when they absorb or emit light. He considered the simplest atom, hydrogen, which has one electron. Bohr proposed that an electron is found only in specific circular paths, or orbits, around the nucleus.

What are atomic orbitals?

Solving the Schrodinger equation gives the energies an electron can have. These are its energy levels. For each energy level, the Schrodinger equation also leads to a mathematical expression, called an atomic orbital, describing the probability of finding an electron at various locations around the nucleus. An atomic orbital is often thought of as a region of space in which there is a high probability of finding an electron.

The way the QMM describes the electron moving around the nucleus is similar to describing a rotating airplane propeller blade. Explain.

The electron cloud of an atom is compared to a spinning airplane propeller in that the airplane propeller is somewhere in the blurry region it produces when spinning at high speed but you can't tell the exact location of the propeller at any instant. Similarly, the electron cloud of an atom represents the locations where an electron is likely to be found.

Explain how the fixed energy levels of electrons are somewhat like the rungs of a ladder.

The lowest rung of the ladder corresponds to the lowest energy level. A person can climb up or down the ladder by going from rung to rung. Similarly, an electron can jump from one energy level to another. A person on a ladder can't stand between the rungs just as electrons in an atom can't be between energy levels. To move from one rung to another, a person climbing a ladder must move just the right distance. To move from one energy level to another, an electron must gain or lose just the right amount of energy. In general, the higher an electron is on the energy ladder, the farther it is from the nucleus.

Rutherford's atomic model also could not explain the ___ properties of elements.

chemical

Explaining what leads to the ___ properties of substances requires a model that better describes the behavior of ___ within atoms.

chemical; electrons

Rutherford's model explained only a few simple properties of atoms. It could not explain, for example, why metals or compounds of metals give off characteristic ___ when heated in a flame, or why objects--when ___ to higher and higher temperatures--first glow red, then yellow, then white.

colors; heated

Because of the spherical shape of an s orbital, the probability of finding an electron at a given distance from the nucleus in an s orbital does not depend on ___. The 3 kinds of p orbitals have different orientations in space.

direction

After discovering the nucleus, Rutherford combined what was known about the atom by proposing an atomic model in which the ___ move around the nucleus, like the planets move around the sun.

electrons

In the Bohr model, each possible electron has a specific ___.

energy

The specific energy an electron can have are called ___ levels.

energy

The 2p sublevel is of higher energy than the 2s and consists of three p orbitals of ___ energy.

equal

In the QMM of the atom, the probability of finding an electron within a certain volume or space surrounding the nucleus can be represented as a ___ cloud. The cloud is denser where the probability of finding the electrons is ___ and the cloud is less dense where the probability of finding the electron is ___.

fuzzy; high; low

Even though the Bohr model gave results that agreed with experiment for the ___ atom, it still failed in what ways?

hydrogen; it failed to explain the energies absorbed and emitted by atoms with more than one electron.

Different atomic orbitals are denoted by ___.

letters

The Rutherford and Bohr models of the atom are based on describing paths of moving electrons the same way you describe the path of a large, ___ object. New theoretical and experimental results were ___ with describing electron motion in this way.

moving; inconsistent

In general, the higher the electron is on the energy ladder, the farther it is from the ___.

nucleus

The energy levels of electrons in the QMM are labeled by principal quantum ___ (n).

numbers

Four of the five d orbitals have the same shape but different ___ in space.

orientations

The long axis of each dumbbell-shaped p orbital is ___ to the other two.

perpendicular

How likely it is to find the electron in a particular location is described by ___.

probability

Each energy sublevel corresponds to orbitals of different ___ describing where the electron is likely to be found.

shapes

These are assigned the values n=1,2,3,4,5,6, and so forth. For each principal energy level, there may be several orbitals with different ___ and different ___levels.

shapes; energy

s orbitals are ___, and p orbitals are ___-shaped

spherical; dumbbell

The numbers and kinds of atomic orbitals depend on the energy ___. The lowest principal energy level (n=1) has only ___ sublevel, called 1s.

sublevel; one

The principal quantum number (n) always equals the number of ___ within that principal energy level.

sublevels

These energy levels within a principal energy level constitute energy ___.

sublevels

What is a quantum of energy?

the amount of energy required to move an electron from one energy level to another energy level. The energy of an electron is said to be quantized. The term "quantum leap" describes an abrupt change. The term comes from the ideas found in the Bohr model of the atom.