Describe how an atom of iron joins up to other atoms in an iron bar

In iron (and other so called ferromagnetic materials), the atoms exhibit a property called long range ordering, where the unpaired electrons align in the same direction to produce a strong magnetic domain. In the presence of a small external field, all of these domains will align in the same direction to produce a large scale magnetic field.

You can read a very nice description of ferromagnetism (along with some nice diagrams) at
http://hyperphysics.phy-astr.gsu.edu/hba…

The connections between iron atoms change with temperature, and with the other non- iron atoms they are mixed with. You have probably noticed that coat hangers (iron) are easily bent while saw or knife blades (also iron) are flexible but more likely to break than bend. This is partly due to heat treatment and partly due to alloying (mixing in atoms of other elements with iron).
Iron atoms have an orderly structure in an iron bar and stack up in a way similar to oranges in a fruit market. For lots of interesting facts and details on iron, check Iron at Wiki, and allotrope's of iron ( at Wiki) for pictures of irons crystal structure.