Do you follow trends? We sure hope so. Currently, there are seven very popular ones in our chemistry unit. They are reactivity, ion charge, melting point, atomic radius, ionization energy, electronegativity, and density. Sound interesting?
Elements close to each other on the periodic table exhibit similar characteristics. The first is reactivity. By this, we are referring to chemical reactivity. We watched a video where only two grams of Cesium reacted violently with water. In class, we saw sodium do the same thing, except it was on a smaller scale and did not blow up our class. Important points to remember for reactivity are:
- Francium is the most reactive metal.
- Fluorine is the most reactive non-metal.
An exception to this trend are the noble gases, which are the least reactive of all elements.
The next trend is ion charge. Element charges depend on their group (column). Let’s look at the lithium atom and ion. Remember, when an atom loses electrons, it becomes smaller. The radius of a lithium atom is larger than that of a lithium ion. The loss of electrons not only vacates the atom’s largest orbitals, it also reduces the repulsive force between the remaining electrons, allowing them to be pulled closer to the nucleus.
Next up we have the melting point. Elements in the centre of the table have the highest melting point. Noble gases have the lowest melting points. Starting from the left and moving right, melting point increases until the middle of the table. Tungsten has the highest melting point of these metals. An exception is carbon, which has a high melting point due to the strong covalent bonds between carbon atoms.
Do you notice a trend in the picture below?
Other than an increase in melting point from the first element to the bottom, we weren't able to find anything out either.
Continuing, a carbon double bond has more force than a carbon single bond. However, the actual single bond has more strength than one of the two bonds of the double bond. This pattern continues for a triple bond. But overall, a triple bond is stronger than a double bond.
Up next is atomic radius! The radii decrease to the up and right of the periodic table. Helium has the smallest atomic radius, whereas Francium has the largest.
Next is ionization energy. Ionization energy is the energy needed to completely remove an electron from an atom. It increases going up and to the right. All nobles gases have high ionization energies. Helium has the highest ionization energy. Francium, on the other hand, has the lowest ionization energy. This trend is opposite to that of atomic radius.
And finally, we have electronegativity! Electronegativity refers to how much atoms want to gain electrons. This is the same trend as ionization energy.
You may be wondering what electron affinity is. Well, it is simply the energy required to add an electron to an atom. An atom’s electron affinity is the energy change that occurs when it gains an extra electron. You can think of electron affinity as a measure of an atom’s attraction, or affinity, for an extra electron. However, be sure that you understand the sign convention. Atoms that have a greater attraction for an added electron have a more negative electron affinity.
Did you know that Francium is electropositive, meaning that it wants to lose electrons?
Posted by Andrew.
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