2.2 MICROSTRUCTURES
To consider materials properly we must start with the basic atomic structure and then look at the more macroscopic aspects, and how they are related to the microscopic components.
2.2.1 Atomic Structures
In an atom there are some fundamental ratios,
The number of protons and neutrons in an atom are equivalent and these determine the atomic number. If there are additional neutrons in the nucleus this is called an isotope.
The mass of the atom is determined by the sum of the neutrons and protons (the electron mass is much smaller).
How these components fit together is described in models,
The valences of electrons are determined with the 'spdf' numbers.
The basic atomic elements are listed in the periodic table. This is in sequence of the atomic masses, as well as proton counts. It can also be used to determine similarities in properties by proximity in the table.
In the periodic table the metals are in the left hand side. They have 1 to 3 valence electrons. They tend to give up electrons when bonding.
In the upper right hand of the periodic table are the non-metals. They typically are 1 to 3 valence electrons short of a full valence level. As a result they tend to consume electrons when bonding. These are,
There is a band of semimetals - including semiconductors. These often consume and give up electrons when bonding. These are
2.2.1.1 - Crystal Structures
HòˆòÈUnderstanding crystal structures can help understanding of crystalline materials such as metals.
Think of dropping balls into a box. it can fall randomly, but often it will fall into patterns. This is like atoms in a solid.
If all of the balls fall into a single organized pattern then we can say there is a single crystal.
Three of the basic structure types to consider are,
In a common solid there will be many regions in the crystal, but there will also be boundaries where the crystal properties change. These are known as boundaries.
A common effect that can occur is slippage along one of the planes of the crystal. An example is pictured below,
Different crystal structures will result in different possible slip planes.
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