Chemical Bonds Also Known As… “The first rule of Fight Club, is nobody talks about fight club!” Bond…Chemical Bond A chemical bond is the term used to describe the electrostatic attraction between pairs of atoms or ions. When you look at an atom or ion, you will see that the nucleus has all of the protons and neutrons while the orbits/shells have the electrons. Now if you picture two atoms or ions approaching one another – it makes sense that “collision” point is going to be the outermost orbit/shell of electrons. These electrons in the outermost orbit of an atom or ion are called the valence electrons and they are the first line players in the bonding game. Their actions are going to dictate the type of chemical bond that is formed between the two atoms or ions. The Octet & The Nobles Rule! The octet rule states that atoms tend to form ions that have a full outer electron shell. This configuration is known as a noble gas configuration and it gives stability to the ion. Even when atoms share electrons (as in the covalent bond) they share only enough electrons to make their outer shells full to capacity with electrons. All electron shells/orbits are full when they have eight (8) electrons in them – except for the first shell/orbit – it only needs two electrons to fill it. The important thing to know here is that there is a great deal of stability associated with having a full outermost shell of electrons – the way the Noble gases do. You could think of it as if the other elements all want to become full of electrons like the Nobles. The Nobles have it all and the other elements are like peasants trying their best to become a Noble. Nobles are stable so they don’t bond – they won’t risk upsetting the balance of their full outer orbit of electrons. Chemistry Fight Club! Remember the term “electronegativity” – it’s the “electron-grabbing strength” of an atom when it’s in a chemical bond. It is going to help us decide what type of bond will be formed between two atoms. The more electronegative you are – the bigger an atomic bully you are! If you are not very electronegative – you’re a wimpy element waiting to get beat up. When we determine what type of bond is going to be formed between two atoms, we compare their electronegativity values and see what is going to happen in chemistry fight club tonight! The types of bond that could be formed at chemistry fight club are: The Ionic Bond The Covalent Bond The Polar Covalent Bond Ionic Compounds Bully beats wimp and steals toys! Ionic compounds are substances that consist of positive ions and negative ions held together by electrostatic attractive forces. [Opposites attract] Ions are formed when atoms lose or gain electrons. They gain them or lose them as a result of chemistry fight club! The nonmetal has a much greater electronegativity than the metal so it simply beats the metal up and takes the electrons its needs to become “Noble”. The nonmetal gains electrons and become a negatively charged ion. The metal loses electrons and becomes a positively charged ion. Ironically, both the “bully” and the “wimp” end up as “Nobles” as result of this electron stealing. Ionic Bond Formation Covalent Bonds Two bullies share the toys! Covalent bonds are chemical bonds that hold nonmetals together through the sharing of pairs of electrons. Nonmetals have high electronegativities – this can result in two “bullies”, of very similar strength, fighting it out and coming to a tie – so they agree to share the electrons with each atoms donating one electron to the bond. The nuclei of the atoms – full of positive protons – are attracted to the shared pairs of electrons. It is possible for two pairs of electrons to be shared between two nonmetals – this results in a double bond. If three pairs of electrons are shared – you get a triple bond. Covalent Bond Formation Covalent vs. Ionic Sharing vs. Taking The Polar Covalent Bond Bully and sidekick share toys unequally! A polar covalent bond is the result of two nonmetals sharing pairs of electrons in an unequal manner because one of the nonmetals is stronger than the other nonmetal. One has more “electron-grabbing strength” than its partner but not enough to just rip them away. The electrons tend to stay closer to the stronger atom and therefore, it tends to carry a slight negative charge. The weaker atom ends up with a slight positive charge. This separation of charge within the same molecule is known as a dipole. Disney villains are great examples of polar covalent relationships…Think of Gaston & Le Fou from Beauty and the Beast – they both pillage and plunder the village but when it comes time to reap the rewards – Gaston gets the bigger take! Polar Covalent Bond Formation The Rules of Chemistry Fight Club Obviously, the first rule of chemistry fight club is nobody talks about chemistry fight club! The second rule of fight club is…The type of bond that you form with another atom depends on the difference between your electronegativity values – this difference is known as the ionic character. 00.3 Covalent 0.41.7 Polar Covalent >1.7 Ionic To figure out the ionic character between two atoms, you simply subtract the smaller electronegativity value from the larger one. Examples: HCl 3.0 – 2.1 = 0.9 Polar Covalent NaCl 3.0 – 0.9 = 2.1 Ionic Cl2 3.0 – 3.0 = 0 Covalent THE END!