Properties and sub-atomic structure
Ions and electronegativity
In the periodic table, it was shown that a metallic element becomes more reactive towards the bottom and towards the left of the table and that, apart from the noble gases, a non-metal becomes more reactive towards the top and right of the table. Combining this with knowledge of the energy levels in the electron shell model, notice that these rules relate.
See animation 1.
Francium is the most reactive metal. Firstly, as with all group I elements, its lone valence electron sits outside a completed shell, which weakens the pull of the protons in the nucleus. Secondly, it takes less energy to remove an electron if the shell it occupies sits further away from the nucleus. Since francium's outermost shell is so far away from its nucleus, it is especially easy for francium to lose its valence electron. Metals want to give away their valence electron/s, so the weaker the attraction to the nucleus, the easier it is to give away the electron/s. See image 1.
Conversely, for non-metals, the most reactive element is fluorine, which is also the lightest of the halogens. Remember that halogens have a high electronegativity and therefore readily gain electrons. Electronegative elements want to gain electrons to complete their outer shell, so it is beneficial for fluorine that there are no completed shells between its nucleus with the positive attraction and the electron it wants to attract. This follows for other elements, where the most electronegative have the strongest positive pull. See image 2.
Conductivity
One of the properties of metal is that it is a good conductor of heat and electricity. Similarly, acids are also good conductors of electricity. Both of these substances contain free-moving particles that readily convey the given energy.
At a sub-atomic level, many of the structural properties of metal come from the charge between its particles called an electrostatic force. This force works on the principle that ions that are oppositely charged will attract each other and ions with the same charge will repel each other. Because metal readily loses electron/s, the free-moving electrons readily conduct heat and electrical energy.
An ionised solution is one that contains cations and anions that have split apart from their substance and which can move freely in the solution. Only ionic solutions conduct electricity because ions carry a charge that we harness as electrical energy. When a solution is used in this manner, it is called an electrolyte.
See animation 2.
In conducting electricity, positive and negative electrodes placed across from each other will attract opposite charges; the positive electrode will attract negative ions and the negative electrode will attract positive ions. The current produced by the movement of the ions results in electrical energy, which stops when the electrodes have attracted all of their opposite ions. See image 3.
Radioactivity
In the late 19th century, French scientist Henri Becquerel discovered the radioactive properties of uranium. Radiation is the emission of energy from a substance in waves or particles. Not all radiation is dangerous, but many radioactive elements can alter the structure and operation of cells, which risks damage to living tissue. Radiation is absorbed every day from sources like the sun. Radiation is used in fields such as medicine (X-rays).
Following Becquerel's discovery, Marie Curie coined the term 'radioactivity' to describe the energy released by the uranium. This led to closer examination, including the decay of an unstable nucleus into a more stable substance. A radioactive element is one that has no stable, naturally occurring isotope that will emit sub-atomic particles in order to achieve stability. Radioactive elements have large atoms, which partly accounts for their instability. They include elements such as francium, polonium, radium and curium. See image 4.
Radioactive emissions are measured in terms of the element's half-life, that is, the time it takes for the element to break down, or decay to half its size. Understanding this sub-atomic energy forms the basis for nuclear physics. Nuclear physics has the helpful applications of nuclear power and the treatment of cancer, but with negative effects such as health problems and questionable environmental impact.
