Compounds and Bonding

Compounds  Compounds = contains two or more different elements chemically bonded together  Most elements are in the form of a compound, very rarely as a single element  Mixture = contains two or more elements or compounds that ARE NOT bonded together

Common Compounds  Salt – NaCl (sodium + chlorine = sodium chloride)  Sugar – made up of Carbon, Hydrogen, and oxygen  Sucrose, glucose, fructose…

Properties of Compounds  Properties come more from the structure and composition rather than the elements themselves  Example: Aspirin – made up of oxygen, hydrogen and carbon. So is formaldehyde and polyethlyene (plastic wrap). They even have the same chemical formulas. The properties of aspirin as a pain reliever come from the combination the shape and the bonds

Chemical Bonds  There are two types of chemical bonds:  1. Covalent Bonds: valence electrons are shared between two or more elements  NONMETALS  2. Ionic Bonds: valence electrons are transferred from one element to another  Metal and a Nonmetal  Bonds will be shown by lines or dots. Each line or dot represents and electron

Chemical Formulas  Identifies the number and element of each type of atom in a compound.  CH 4  H 2 O  CO 2

Covalent Bonding  SHARED ELECTRONS  A group of covalently bonded compounds is called a MOLECULE  Typically non-metals bonding to other gasses or non-metals  Double and Triple Bonds – represent multiple electrons

Ionic Bonding  When an electron is either lost or gained (transferred)  ALMOST ALWAYS includes one metal (metals are conductors – they will always LOSE their electron!)  One electron is transferred from a metal to a non- metal  The bond is based on electrical attractiveness  Positive attracting a negative

Ionic Bonding Cont’d  When an element gains or loses an electron, it becomes an ION  For example: Salt!  Sodium (Na) is a metal. When it bonds with Chlorine (Cl), Na will lose its one valence electron.  Na becomes a positively charged ion, because it lost an electron  Cl becomes a negatively charged ion, because it gained an electron  Another example: MgCl 2  DOES NOT BECOME A MOLECULE! Ionic bonds are not limited to one element each, because of the charges, they will be attracted to all neighboring ions.

Hints to remember  An element will bond with as many other elements as it has valence electrons  4 valence electrons means it can make 4 other bonds (wants to get to 8 and be happy!)  3 valence electrons means it can make 5 other bonds  Covalent bonds are SHARED and form MOLECULES  Typically non-metals bonding together in long, complex chains and compounds  IONIC bonds form IONS!!! Based on charges and gaining and losing electrons  Metals bonding with non-metals

Energy in Bonding  Free atoms contain a large amount of energy  This energy is lost when they bond to another element  Energy is released when chemical bonds form  Some elements are more reactive (willing to form bonds and compounds) then others.  The closer you are to the noble gasses, the more reactive!  Na is highly reactive (1 electron away) and so is Cl (1 electron away). But these elements in pure form together create an explosion!