
Why do metals want to return to lower energy
state? Does it make them more stable or something?
If so, why do they want to be stable? 
Question Date: 20130424   Answer 1:
It's not just metals that tend towards a lower
energy state. Most things in an isolated system
obey the second law of thermodynamics, which
basically states that the entropy of the universe
never decreases. This means that entropy is always
maximized, which in turn means that energy is
always minimized (this relationship can be derived
from the first law of thermodynamics). Why is
entropy maximized in an isolated system?
Let's look at the equation for entropy:
"S = k Log(omega)"
where S is the entropy, k is Boltzmann's constant,
and omega is the "density of states" or basically
the number of "microstates" available to a system.
A microstate is any possible arrangement of the
microscopic degrees of freedom in a system, such
as the particle positions or the momenta of the
particles. It turns out that more microstates are
available where certain values of the energy,
volume, and number of particles are adhered to by
the system: let's call them E*, V*, and N* where
the number of microstates is maximized (let's call
it omega*). Since there are more microstates
available at E*, V*, and N*, the system is more
likely to be at E*, V*, and N*.
If that doesn't make sense, think about having a
bag of 10 marbles, 9 black and 1 white. You're
more likely to pick a black one than a white one,
right? Well if omega* is larger than other
omega's, then omega* is where the system is more
likely to be. When we maximize omega, the number
of microstates, we are maximizing the entropy,
since the logarithm of a large number is larger
than the logarithm of a small number (if you don't
believe me, type log(100000) into your calculator,
and compare the result to log(10), for example).
Now remember, when we maximize entropy, this
corresponds to minimizing energy. So at the heart
of things, it's a matter of the system existing at
the values of E, V, and N that maximize the number
of microstates and entropy. This in turn happens
to be where the system is most "stable" in the
sense that this is where the system tends to
evolve toward. I hope that helps.
  Answer 2:
Great question! When metal atoms absorb an
electron, photon, or other particle with energy,
they become excited. You can think about this as
the metal atom becoming very agitated and vibrates
quickly, disturbing its neighbor atoms. Because
of this excess energy, the nearby atoms want to
equilibrate with this excited atom, and so the
metal atom transfers its energy through to the
neighbors and itself is now lowered in energy
(returning to a more stable state). This process
of transferring excess energy throughout the metal
is attributed to the increase in temperature of
the metal. Other ways for the atom to return to
stable state is to give off energy in the form of
radiation (i.e. light or heat). This is why
metals seem to “glow” when they are heated at a
very high temperature.
  Answer 3:
This is not just true of metals. In fact every
system wants to minimize its total internal energy
and dissipate the extra energy into its
surroundings because of the second law of
thermodynamics. In the case of an atom, the
electromagnetic force is pulling the electrons
towards the nucleus, so the further away the
electrons from the nucleus, the greater the
potential energy of the atom. But there are only
certain orbitals (or quantum states) that
electrons can occupy, and they can't occupy the
same orbital (this is called the Pauli exclusion
principle). So for a given number of electrons,
the most stable atomic state is to fill in the
orbitals starting from the lowest energy one. If
an electron is excited to a higher energy orbital,
it will want to quickly go back to a lower
available one. Also, for metals specifically,
since they typically have one or two electrons in
the outermost shell, if they lose an electron or
two they will have lower energy (classically an
empty or full shell is lower energy than partially
full). Thus they like to form ionic bonds in which
they lose electrons.
Source:
1) http://en.wikipedia.org/wiki/Excited_state
2) http://en.wikipedia.org/wiki/Ionic_bond
  Answer 4:
This is called the second law of
thermodynamics: any system will move from a more
ordered state to a less ordered state. By moving
to a lower energy state, the potential energy that
was stored in the metal is released to become
kinetic energy. Kinetic energy is less ordered
than potential energy, and so is favored by
thermodynamics.
  Answer 5:
All systems "want" to be in their lowest energy
configuration. Take for example a ball on a hill.
A ball on a hill will roll down the hill until it
reaches the bottom of the hill. In the process,
the ball is reducing its potential energy
(Eg=m*g*h where m=mass of the ball, h=height, and
g=the gravitational acceleration). Systems respond
to gradients in potential energy be they chemical,
gravitational, electrical, or etc. Such gradients
produce forces and these forces drive changes in
the system. In the example above, there is a
gravitational force on the ball due to the change
in gravitational potential energy with height
(gradient in gravitational energy). If there is no
net force acting on a system, then the systems
configuration will not change. Such occurrences
can be stable, metastable, or unstable. Picture a
pendulum balance precariously straight up. The net
for will be zero (the gravitational force is
balance exactly by the support holding the
pendulum up), but as we know, this situation is
not stable. Any small variation or perturbation in
the pendulum about its current position will
result in a net force away from that position.
This is the definition of an unstable equilibrium
position (i.e. the net force is zero, but any
perturbation will cause the system to move away
for this point). A stable equilibrium position is
when the net force on the system is zero, and any
small perturbation about the systems position will
result in a force which moves the system back
towards the equilibrium position. Picture here the
pendulum at rest at the bottom of its swingany
small perturbation about this position will result
in the pendulum swinging back down towards the
equilibrium position at the bottom of the swing.
The metastable equilibrium is like the stable
equilibrium in that small perturbations will
return the system to the metastable state;
however, sufficiently large perturbations will
result in the system moving out to another
metastable or stable state. Picture here a ball in
a hole on the side of a hill. If the ball rolls
around in the hole it is stuck (held in the
metastable state); however, given enough energy,
the ball could be kick out of the hole and would
then roll farther down the hill. In summary,
systems respond to forces which are the results of
gradients in some potential energy function. The
forces act to move the system to lower energy
states. The state of a system can be classified as
stable, unstable, or metastable depending on the
effect that variations around that point have on
the evolution of the system.
  Answer 6:
Everything in nature will try to achieve the
most stable state, which we define as the state
with the least "free energy." Free energy is
energy that can do work. For example, water flows
downhill to minimize its gravitational energy,
salts dissolve in water to maximize their entropy
(entropy is a measure of how many ways something
can exist, and can be thought of as a measure of
randomness or disorder. Something that is more
disordered has less energy.), air currents flow
and mix to maximize their entropy, wood and other
fuels burn to minimize their chemical energy,
batteries discharge to minimize their chemical
energy. It's not that these things "want" to be
stable, it's just that these processes will happen
because there is free energy to do something (for
example, to burn, or to flow downhill), and once
that happens, the system is trapped in a new,
lower energy state. (Until it can do something to
lower its energy even further.)
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