Chemistry: Chemical Bonding

We made molecules in the last post, with each marshmallow representing an atom. But for older students, you need to look more closely at the atoms themselves to understand how molecules form. On the most basic level, atoms are made up of three parts, the protons and neutrons in the core of the atom, and the electrons which circle it in the electron cloud. The electron cloud is really made up of several smaller clouds called orbitals. This is the basis of chemical bonding.

Electrons on one atom are attracted to the protons on another atom.

There are several types of orbitals; s orbitals are spherical in shape, p orbitals are more pear shaped and d, f and other orbitals are too complicated (until upper level college chemistry courses) to identify their shape, so are just labeled by the letters. Orbitals not only come in different shapes, but also different sizes. 1 orbitals are small, 2 orbitals are larger and 3 orbitals are larger still, and so on. So, a 1s orbital is a small spherical shaped orbital.

So, with this in mind, we can picture the Hydrogen atom, which on the Periodic Table of Elements is in the first position, and labeled as 1, as having a small spherical shaped orbital in which its one electron moves in.

from Real Science 4 Kids Chemistry, Level IIWhen we talk about p orbitals, since they are pear (or more dumb-bell) shaped they have two lobes and a narrow waist in the middle, the orbitals can be pointed in different directions, each one perpendicular to the others. These are labeled x, y and z to differentiate them from each other.

from Real Science 4 Kids,Chemistry, Level II

If you look at the Periodic Table of Elements, each new atom has all the electrons of the previous atom, plus one more. The full list of all the electrons in their orbitals is called the electron configuration of the atom. The electron configuration is given by listing the orbital in the same sequence as they were filled.chart from Friendly Chemistry

Each row in this chart above represents what is called a subshell. For 2p, for example, to have its subshell filled there must be two electrons,in each circle of the row or in each the x, y and z orbitals.
Nobel gases are all in the last column of the Periodic Table. They have all of their subshells completely filled.

All of the elements refer to the previous nobel gas. For example, all of the elements of second row, have the same electron configuration as the noble gas helium, which is the nobel gas on the first row, plus some extra electrons. These extra electrons are called valence electrons.

Having no valence electrons, nobel gases are highly unreactive. They rarely form chemical bonds with other atoms. It is these valence electrons that are responsible for basically all chemical reactions.

It can become tedious to write out every shell and their electrons, so to simplify the filled shells are often represented using brackets and the symbol for the noble gas of the previous row. The only electrons listed are the valence electrons.

Next post in this series: The Aufbau and Pauli Principles