Download Ch. 5.1 Models of the Atom

Ch. 5.1 Models of the Atom
The Development of Atomic Models
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Rutherford’s model, with the protons and
neutrons in a nucleus surrounded by electrons,
couldn’t explain the chemical properties of
elements.
Niels Bohr proposed that an electron is found
only in specific circular paths around the
nucleus, in fixed, exact energy levels.
Electrons must gain or lose exact amounts of
energy (quantums) to change energy levels.
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An analogy of Bohr’s energy levels would
be the rungs on a ladder, except the rungs
would not be evenly spaced. The higher
rungs (energy levels) would be closer
together.
The Quantum Mechanical Model
Experimental results were inconsistent
with the idea of electrons moving like large
objects in orbit.
 Schrodinger proposed the quantum
mechanical model. It does not involve the
exact path an electron takes around the
nucleus.
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The model determines the allowed energy
an electron can have, and how likely it is
to find the electron in various locations
around the nucleus.
Atomic Orbitals
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Schroeinger’s equation gives the energy levels
an electron can have, but also describes the
probability of finding an electron at various
locations around the nucleus, called atomic
orbitals.
Energy levels are labeled by principal quantum
numbers (n). n = 1, 2, 3, etc.
Several orbitals with different shapes and energy
levels (sublevels) exist within each principal
energy level.
Each energy sublevel corresponds to an
orbital of different shape describing where
the electron is likely to be found.
 Different atomic orbitals are denoted by
letters…s, p, d, f.
 s orbitals are spherical; p orbitals are
dumbbell-shaped. The three kinds of p
orbitals have different orientations in
space.
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Other orbitals have different and more
complex shapes.
 When n = 1, it has one sublevel…1s.
 n = 2 has two sublevels…2s and 2p.
 n = 3 has three sublevels…3s, 3p, and 3d.
 n = 4 has four sublevels…4s, 4p, 4d, 4f.
 The principal quantum number always
equals the number of sublevels within that
principal energy level.
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The maximum number of electrons that
can occupy a principal energy level is
given by the formula 2n2.