IB Honors Chemistry II Cook

 You already know how ions are formed by the loss or gain of electrons  Covalent bonds are the result of electron sharing between atoms.  A good example of covalent bonding is the water molecule  Atoms of hydrogen and the non metallic elements of groups 4A, 5A, 6A and 7A are prone to form covalent bonds

 The sharing of electrons occurs when the atoms involved can thus acquire stable electron configurations.  Hydrogen is the simplest molecule and has a single valence electron  Sharing electrons

 Can you see and understand how it is covalent?

 Review:

 A chemical element is identified by the number of protons in its nucleus, and it must collect an equal number of electrons if it is to be electrically neutral.  As electrons are added, they fill electron shells in an order determined by which configuration will give the lowest possible energy.  The first shell (n=1) can have only 2 electrons, so that shell is filled in helium, the first noble gas.  In the periodic table, the elements are placed in "periods" and arranged left to right in the order of filling of electrons in the outer shell.  So hydrogen and helium complete the first period.

 Hydrogen bonded to hydrogen is a good example of a single covalent bond  A single covalent bond is formed when a pair of electrons is shared between two atoms  It is helpful to show a pair of electrons in a covalent bond with a dash –  Dashes are equivalent to 2 dots  Structural formulas:  Are chemical formulas that show the arrangement of atoms in molecules and polyatomic ions.  Be careful of diatomic ions (table 14-1)

 Atoms can sometimes share more than one pair of electrons to become stable/noble gas configurations.  Double Covalent bonds= 2 shared pairs of e -  Triple Covalent bonds= 3 shared pairs of e -  Oxygen is an example of a molecule that should have a double bond.  Oxygen with 6 valence electrons could share two of these with another oxygen

 Nitrogen contains a triple covalent bond. Each nitrogen has 5 valence electrons, they need 3 more to attain neon configuration

 Become familiar with it: