To Bond or Not to Bond That’s the Question  You can use the periodic table to determine the number of valence electrons.  Group 1 has 1 valence electron.  Group 2 has 2 valence electrons  Groups 3-12 do not have a rule relating their valence electrons to their group number.  Groups have 7or less valence electrons.

 Not all atoms bond in the same way.  Some don’t bond at all.  The number of valance electrons determines whether or not they will bond.  The noble gases (group 18) do not usually form chemical bonds. They already have 8 valence electrons.  Their outermost energy level is considered full.

 An atom with fewer than 8 valence electrons is much more likely to form bonds.  Atoms gain, lose, or share electron in order to have a filled outermost energy level.  There is an exception to this. Helium only needs only two valence electrons.  Hydrogen and Lithium have one valence electron. Therefore, they bond by gaining, losing or sharing electrons to achieve 2 electrons in their first energy shell.

Sulfur has 6 valence electrons. It can have 8 by gaining 2 electrons or by sharing two electrons from other atoms.

Magnesium has 2 valence electrons. It can have a full outer level by losing 2 electrons. The second energy level becomes the outermost energy level and contains 8 electrons.

Ionic Bonds  A bond that is formed when electrons are transferred from one atom to another atom.  One or more valence electrons is transferred from one atom to another.  The outermost energy levels of the atoms in the bonds are filled.

Charged Particles  Ions are charged particles that are formed when an atom gains or loses electrons.  An atom cannot gain electrons without another atom nearby to lose electrons or cannot lose electrons without a nearby atom to gain them.

 Ionic bonds are formed when atoms pull electrons away from other atoms.  Atoms that lose electrons now have fewer electrons than protons and now have a positive charge.  Atoms of metals have few valence electrons so they tend to lose them and become positive ions.

Ionic Bond BBetween atoms of metals and nonmetals with very different electronegativity BBond formed by transfer of electrons PProduce charged ions all states. Conductors and have high melting point. EExamples; NaCl, CaCl 2, K 2 O

Ionic Bonds: One Big Greedy Thief Dog!

Sodium (Na) has only one valence electron. It can lose its 1 electron to another atom. The second energy level becomes its filled level. Now sodium has one more proton than electron so it has a positive charge. The sodium ion is 1+ charge and is written as Na +

Forming Negative Ions  Some atoms gain electrons during chemical changes. When this happens, there are more electrons than protons thus forming a negative charge.  Nonmetals gain electrons.

Oxygen has 6 valence electrons. It needs two more in order to fill its outermost shell. It will gain 2 electrons from another atom. Now the outermost energy level is filled. Since it has 2 more electrons than protons, it becomes an oxide ion that has a 2- charge. the symbol for the oxide ion is O 2-

 -ide is used for the names of the negative ions formed when atoms gain electrons.

Covalent Bonding  Forms when atoms share one or more pairs of electrons.  Remember water?  Oxygen has 6 valence electrons and needs 2 more. Hydrogen has 1 valence electron and need one more to have a full shell. So they share electrons.

Covalent Bond  Between nonmetallic elements of similar electronegativity.  Formed by sharing electron pairs  Stable non-ionizing particles, they are not conductors at any state  Examples; O 2, CO 2, C 2 H 6, H 2 O, SiC

when electrons are shared equally NONPOLAR COVALENT BONDS H 2 or Cl 2

2. Ionic Bonds - Draw the Lewis structures for each atom, draw arrows to show the transfer of electrons, write the charge for each ion, and then write the chemical formula. (A)Potassium + Iodine (B) Magnesium + Oxygen (C) Lithium + Nitrogen

3. Covalent Bonds – Draw the Lewis structures for each atom, draw circles to show the electrons that are shared, and then write the bond structure and chemical formula. (A)Fluorine + Fluorine (B) 3 Hydrogen + 1 Phosphorus (C) 2 Hydrogen + 1 Sulfur