Chapter 4: Periodic Properties of the Elements

Why it matters: Periodic properties of the elements

Electric currents in the vastly complex system of billions of nerves in our body allow us to sense the world, control parts of our body, and think. These are representative of the three major functions of nerves. First, nerves carry messages from our sensory organs and others to the central nervous system, consisting of the brain and spinal cord. Second, nerves carry messages from the central nervous system to muscles and other organs. Third, nerves transmit and process signals within the central nervous system. The sheer number of nerve cells and the incredibly greater number of connections between them makes this system the subtle wonder that it is. Nerve conduction is a general term for electrical signals carried by nerve cells. It is one aspect of bioelectricity, or electrical effects in and created by biological systems. Figure 1 illustrates how a voltage (potential difference) is created across the cell membrane of a neuron in its resting state. This thin membrane separates electrically neutral fluids having differing concentrations of ions, the most important varieties being [latex]\ce{Na^{+}}[/latex], [latex]\ce{K^{+}}[/latex], and [latex]\ce{Cl^{-}}[/latex]. (these are sodium, potassium, and chlorine ions with single plus or minus charges as indicated). Free ions will diffuse from a region of high concentration to one of low concentration. But the cell membrane is semipermeable, meaning that some ions may cross it while others cannot and can distinguish based on the size of the ion. The relative size of an ion is a periodic property and can be predicted based on the location of the element on the periodic table. The following chapter will explore periodic properties that will be explained by quantum mechanics, as covered in Chapter 3.

Figure 1: A neuron with its dendrites and long axon. Signals in the form of electric currents reach the cell body through dendrites and across synapses, stimulating the neuron to generate its own signal sent down the axon. The number of interconnections can be far greater than shown here.
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