Download Chapter 5 : Electrons in Atoms

Chapter 5 : Electrons in Atoms
Section 2 Notes
Bohr's Model of the Atom
Section 5-2
Bohr correctly predicted the frequency lines in
hydrogen’s atomic emission spectrum.
The lowest allowable energy state of an atom is called its
ground state.
When an atom gains energy, it is in an excited state.
Bohr's Model of the Atom (cont.)
Section 5-2
Bohr suggested that an electron moves around the
nucleus only in certain allowed circular orbits.
Bohr's Model of the Atom (cont.)
Section 5-2
Each orbit was given a number, called the quantum
number.
Bohr's Model of the Atom (cont.)
Section 5-2
Hydrogen’s single electron is in the n = 1 orbit in the
ground state.
When energy is added, the electron moves to the n = 2
orbit.
Bohr's Model of the Atom (cont.)
Section 5-2
Bohr's Model of the Atom (cont.)
Section 5-2
Bohr's Model of the Atom (cont.)
Section 5-2
Bohr’s model explained the hydrogen’s spectral lines,
but failed to explain any other element’s lines.
The behavior of electrons is still not fully understood, but
it is known they do not move around the nucleus in
circular orbits.
The Quantum Mechanical Model of the Atom
Section 5-2
Louis de Broglie (1892–1987) hypothesized that
particles, including electrons, could also have
wavelike behaviors.
The Quantum Mechanical Model of the Atom (cont.)
Section 5-2
The figure illustrates that electrons orbit the nucleus
only in whole-number wavelengths.
The Quantum Mechanical Model of the Atom (cont.)
Section 5-2
The de Broglie equation predicts that all moving
particles have wave characteristics.
λ represents wavelengths
h is Planck's constant.
m represents mass of the particle.
ν represents velocity.
The Quantum Mechanical Model of the Atom (cont.)
Section 5-2
Heisenberg showed it is impossible to take any
measurement of an object without disturbing it.
The Heisenberg uncertainty principle states that it is
fundamentally impossible to know precisely both the
velocity and position of a particle at the same time.
The only quantity that can be known is the probability for
an electron to occupy a certain region around the
nucleus.
The Quantum Mechanical Model of the Atom (cont.)
Section 5-2
The Quantum Mechanical Model of the Atom (cont.)
Section 5-2
Schrödinger treated electrons as waves in a model called
the quantum mechanical model of the atom.
Schrödinger’s equation applied equally well to elements
other than hydrogen.
The Quantum Mechanical Model of the Atom (cont.)
Section 5-2
The wave function predicts a three-dimensional region
around the nucleus called the atomic orbital.
Hydrogen Atomic Orbitals
Section 5-2
The principal quantum number (n) describes the
size of the orbital. Orbitals for which n = 2 are larger
than those for which n = 1, for example. Because they
have opposite electrical charges, electrons are attracted
to the nucleus of the atom. Energy must therefore be
absorbed to excite an electron from an orbital in which
the electron is close to the nucleus (n = 1) into an
orbital in which it is further from the nucleus (n = 2).
The principal quantum number therefore indirectly
describes the energy level of an orbital.
Hydrogen Atomic Orbitals
Section 5-2
The angular quantum number (l) describes the
shape of the orbital. Orbitals have shapes that are best
described as spherical (l = 0), polar (l = 1), or
cloverleaf (l = 2). They can even take on more complex
shapes as the value of the angular quantum number
becomes larger.
Hydrogen Atomic Orbitals
Section 5-2
There is only one way in which a sphere (l = 0) can be
oriented in space. Orbitals that have polar (l = 1) or
cloverleaf (l = 2) shapes, however, can point in different
directions. We therefore need a third quantum number,
known as the magnetic quantum number (m), to
describe the orientation in space of a particular orbital.
(It is called the magnetic quantum number because the
effect of different orientations of orbitals was first
observed in the presence of a magnetic field.)
Hydrogen Atomic Orbitals (cont.)
Section 5-2
Energy sublevels are contained within the principal
energy levels.
Hydrogen Atomic Orbitals (cont.)
Section 5-2
Each energy sublevel relates to orbitals of different
shape.
Hydrogen Atomic Orbitals (cont.)
Section 5-2
Section 5.2 Assessment
Section 5-2
Which atomic suborbitals have a “dumbbell” shape?
A. s
B. f
C. p
D. d
Section 5.2 Assessment
Section 5-2
Who proposed that particles could also exhibit wavelike
behaviors?
A. Bohr
B. Einstein
C. Rutherford
D. de Broglie