Ionic & Covalent Bonds

 A compound is a substance whose smallest unit is made up of atoms of more than one element bonded together.

 Compounds often have properties that are different from the elements that make them up.  For Example: Water (H 2 O) and Hydrogen peroxide (H 2 O 2 )

The combining of atoms of elements to form new substances is called chemical bonding. Exposed electrons in the outermost shell are responsible for bonding.

 Lewis Dot Structure (also called an electron-dot configuration) Shows valence electrons as a series of dots surrounding an atomic symbol.

Find out which group (column) your element is in. This will tell you the number of valence electrons your element has. You will only draw the valence electrons.

 Atoms will combine to form compounds in order to reach eight electrons in their outer energy level.  Be aware that there are some exceptions!  CONSIDER EIGHT A HAPPY NUMBER FOR ATOMS!

◦ Atoms with less than 5 electrons tend to lose electrons. ◦ Atoms with more than 6 electrons tend to gain electrons.

 In ionic bonding, electrons are transferred between two or more atoms.  Ion- is an atom having a positive or negative charge.

 The atom that loses electrons becomes a positive ion.  Has more protons than electrons.

 The atom that gains electrons becomes a negative ion.  Has more electrons than protons.

 The force of attraction between these oppositely charged ions is an IONIC BOND.  Ionic bonding occurs between a metal and a nonmetal.

 The charge that an atom would have if it lost or gained electrons; ionic charge.  Can be helpful in determining which atoms will interact or bond with each other.  Example: According to electron dot diagram for Magnesium, it has two valence electrons. Because Magnesium is “unhappy” with two, it will typically lose them. If this happens it will turn into a Magnesium ion. At this point it will have an oxidation number of Mg

Na + + Cl -

 In covalent bonding, electrons are shared by two or more atoms.  Covalent bonding usually occurs between atoms of nonmetals.

 The force of attraction between the nuclei of the atoms and the shared electrons is a covalent bond.

 Molecule- any group of atoms held together by covalent bonds.

Ionic bonding  Attraction of opposite charges  Between metal and nonmetal  Ends in an ionic compound Covalent bonding  Formed from force of attraction of nuclei and electrons – Sharing  Between nonmetals  Results in a molecule

 The amount of energy needed to remove an electron from an atom.  The closer the electron is to the nucleus, the harder it is to remove. Weakest for elements on the left of the periodic table, and strongest for elements on the right