Covalent Bonding  Many compounds do not form ionic bonds. These compounds contain two or more non- metallic atoms.  For example, CO 2 is made of two different non-metals, carbon and oxygen. These compounds are formed through the sharing of valence electrons.

 A covalent bond is formed when two or more non-metallic atoms share valence electrons.  Non-metallic atom + Non-metallic atom = covalent bonding

Compounds vs. Molecules  Two non-metallic elements combine to form covalent compounds (or bonds). Compounds contain at least two different types of atoms.  A molecule is the smallest unit of a covalent compound.  A molecule of a compound has different characteristic properties than the atoms which form it.

Example  Two hydrogen atoms form a covalent bond by sharing electrons to produce a hydrogen molecule. A hydrogen molecule still possesses the properties of hydrogen. No new substance is formed since only one type of atom, H, is present.

 By sharing their electrons, both atoms are satisfied they have filled outer orbits (the outer orbits are the same as for helium) and are stable.  The two hydrogen atoms form a diatomic molecule (i.e., two atoms of hydrogen share electrons to make a single molecule of hydrogen gas).

 The elements forming diatomic gases are unstable as single atoms and combine almost instantaneously to form stable molecules.  Note that diatomic molecules are still classified as elements even though they are molecules. While it may seem strange that a molecule is called an element rather than a compound, remember that diatomic molecules are made of only one kind of atom.

Name of Element Symbol for one atom of the element Formula or one molecule of the element HydrogenHH 2(gas) NitrogenNN 2(gas) OxygenOO 2(gas) FluorineFF 2(gas) ChlorineClCl 2(gas) BromineBrBr 2(liquid) IodineII 2(solid)

HINT!!!!  If the diatomic elements are placed in a different order the symbols spell out a word that can help you remember these diatomic elements.  Remember “Count HOFBrINCl”, pronounced as “Count Hoffbrinkle”. If you remember “Count HOFBrINCl” you will never forget which elements are diatomic

Organic Compounds  Covalent bonds can also be classified as organic compounds. This is when 2 non-metallic elements combine together.  Example: e.g. CO, C H O

Diatomic or Organic Compound? Example – If the element was on it’s own... Forms a Diatomic or Organic Compound? Fluorine Carbon Sulphur Hydrogen Helium Chlorine Oxygen

Octet Rule  The only way that two non-metallic atoms can satisfy their need to gain electrons when they bond is through sharing valence electrons. The sharing of electrons between two non- metallic atoms allows each atom to have a complete octet of electrons at least part of the time.  The shared electrons are attracted at the same time to each nucleus in each atom. This is the “glue” that holds the atoms together.  A covalent bond is formed when two atoms share one or more pairs of electrons in order to obtain a complete octet of electrons.

Happy Atoms!