Why does a magnet stick to a metal surface?

Question

i want a complex answer

Answer 1

There are only a few elements in the periodic table that are attracted to magnets.  None of the elements, by themselves, make good permanent magnets, but can become temporary magnets (when close to another magnet).  When alloys of various metals are made, some of these alloys make very good magnets.  Why?  We don't really know, but we can observe some consistent rules.

As you know, we have seen that when current flows in a wire, a magnetic field is created around the wire.  Current is simply a bunch of moving electrons, and moving electrons make a magnetic field.  This is how electromagnets are made to work.  This will be important to keep in mind as we zoom into the structure of atoms.

Around the nucleus of the atom, where the protons and neutrons live, there are electrons whizzing around.  We used to think that they had certain circular orbits like the planets have around the sun, but have discovered that it is much more complicated, and much more exciting!  Instead, the patterns of where we would likely find the electron within one of these orbitals takes into account Schroedinger's wave equations.  Pictures of each of these orbitals can be found at http://www.shef.ac.uk/chemistry/orbitron...  (These also take into account Heisenberg's uncertainty principle and probability theory.)

First, electrons can be thought of as occupying certain shells that surround the nucleus of the atom.  These shells have been given letter names like K,L,M,N,O,P,Q.  They have also been given number names, such as 1,2,3,4,5,6,7.  (This is what quantum mechanics is all about).

Within the shell, there may exist subshells or orbitals, with letter names such as s,p,d,f.  Some of these orbitals look like spheres, some look like an hourglass, others look like beads on a bracelet.  

The K shell contains an s orbital.  Called a 1s orbital.

The L shell contains an s and p orbital.  Called a 2s and 2p orbital.

The M shell contains an s, p and d orbital.  Called a 3s, 3p and 3d orbital.

The N, O, P and Q shells each contain an s, p, d and f orbital.  Called a 4s, 4p, 4d, 4f, 5s, 5p, 5d, 5f, 6s, 6p, 6d, 6f, 7s, 7p, 7d and 7f orbital.

These orbitals also have various sub-orbitals.  

The s orbital can contain only 2 electrons and has no sub-orbitals.

The p orbital can contain 6 electrons, 2 in each of its 3 sub-orbitals, like px, py and pz.

The d orbital can contain 10 electrons, 2 in each of its 5 sub-orbitals, like dxy, dxz, dyz, dz2, dx2-y2.

The f orbital can contain 14 electrons, 2 in each of its 7 sub-orbitals.

(And there is a g orbital that can contain 18 electrons, 2 in each of its 9 sub-orbitals, for highly excited electrons.)

A maximum of 2 electrons can occupy a sub-orbital where one has a spin of UP, the other has a spin of DOWN.  There can not be two electrons with spin UP in the same sub-orbital.  (Pauli exclusion principal.)  Also, when you have a pair of electrons in a sub-orbital, their combined magnetic fields will cancel each other out.

As you can see, the general order for filling the electron orbitals follows a sequence since the energy level for each orbital increases in this sequence: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, 5s, 4d, 5p, 6s, 4f, 5d, 6p, 7s, 5f, 6d, 7p

After each orbital is full, it starts to fill the next one in this sequence.  There are a few odd jumps in the sequence when you get to filling the 4f, 5d and 6p orbitals, but that's how it goes.  

If we were to examine Iron (atomic number 26), Cobalt (27), Nickel (28) and Gadolinium (64), all of which are considered ferromagnetic since they are strongly attracted to a magnet, it is difficult to see what makes them so different from the other elements next to them or below them in the periodic table.  In other words, if Iron is so strongly magnetic, why isn't Manganese?  Perhaps there are other factors we need to take into account such as the crystalline structure.  But it is generally accepted that these ferromagnetic elements have large magnetic moments due to un-paired electrons in their outer orbitals.  This is like having current flowing in a coil of wire, creating a magnetic field.  Even the spin of the electron is thought to create a minute magnetic field.  When you get a bunch of these fields together, they add up to bigger fields.

Iron (Fe)

Atomic Number 26

Electron configuration  1s22s22p63s23p63d64s2

This shows the electron orbits as circular rings around the nucleus.  It really isn't like this, but it makes a good diagram.

The green dot in the center is the nucleus with the 26 protons and 26 neutrons. The orange dots in the 3d orbital are the 4 unpaired electrons.

The unpaired electrons in 3d create a magnetic moment, or force.  It is thought that D/r must be 3 or more to create ferromagnetism.  This condition occurs in Iron, Cobalt, Nickel and rare-earth groups.

We can go one level deeper into quantum mechanics.  This is where we ask, "What is the magnetic field made of?"

Today, there are four basic forces that are known:  gravity, electromagnetism, weak, strong.  What creates these forces?  There is speculation among particle physicists that these forces are the result of photons that are exchanged between particles.  This exchange is what creates a repulsion or attraction between various particles, giving us the forces we call gravity, magnetism, and others that hold the protons together in the center of the atom.  For a more in-depth understanding, you will want to read about the Standard Model of the atom at:

http://particleadventure.org/particleadv... and

http://particleadventure.org/particleadv... and

http://www.schoolscience.co.uk/content/4...