Chemical Bonds

Valence electrons are those electrons in the outermost shell of an atom that can be used to form a chemical bond.

The oxidation states of an element (listed for each element in your periodic table) tell you how many electrons an element will take or give up to form a chemical bond.

Atomic Symbol: C Atomic Name: Carbon Oxidation States: 4, -4, and 2. A negative oxidation state means the element will gain electron(s) from another element. A positive oxidation state means that the element will give up it’s electron(s).

What are the oxidation states for I or Iodine?

-1 Iodine will take 1 electron (leaving a – charge) +1 Iodine will give 1 electron (leaves a + charge) +5 Iodine will give 5 electrons (leaves a + charge) +7 Iodine will give 7 electrons (leaves a + charge) Iodine: -1, 1, 5, and 7. What does each number mean?

All atoms want to have their outermost electron shell filled with electrons. In order to do this an atom will either gain or lose electrons.

All atoms want to follow the Octet Rule: All the atoms in the chemical reaction will seek to have their outer most electron shells filled by either adding electrons to reach 8 or losing all electrons in their outer most shell.

Types of Bonds A Covalent Bond is formed when two atoms share their outermost electrons.

H H Ex: Hydrogen has 1 electron in its outermost shell.

H H In this example of a covalent bond the electrons from the hydrogen atoms can move between the two hydrogen atoms.

H H H 2 is formed because the 2 outermost electrons are shared between the two hydrogen atoms.

Covalent bonds

Type of Bonds (continued) A Metallic covalent bond is formed when atoms share their outermost electrons and the two atoms are both metals.

Metallic Covalent Bond

Type of Bonds (continued) An Ionic bond is formed when one atom transfers its outermost electrons to another atom.

Na Cl How many electrons are found on the outermost electron shell of Na and Cl?

Na Cl Na has 1 electron and Cl has 7 in their outermost electron shell.

Na Cl What would be easier to transfer, 1 electron from Na or 7 electrons from Cl?

Na Cl 1 electron from Na is transferred to Cl.

Na Cl How many electrons and protons does Na have after this transfer? 11(p+) 10(e-)

Na Cl This imbalance gives Na a positive electrical charge. 11(p+) 10(e-) +

Na Cl How many electrons and protons does Cl have after this transfer? 11(p+) 10(e-) +

Na Cl How many electrons and protons does Cl have after this transfer? 11(p+) 10(e-) + 17(p+) 18(e-)

Na Cl This imbalance gives Cl a negative electrical charge. This produces the ionic bond that forms NaCl. 11(p+) 10(e-) + 17(p+) 18(e-) - This is called electrostatic attraction.

They are all gases They are all in the last column of the Periodic Table of Elements They all have their outermost electron shell filled. Looking at your Periodic Table of Elements, what do you notice about the elements, He, Ne, Ar, Kr, Xe, and Rn?

These gases are called Noble or Inert Gases because they will not chemically bond with any other elements because their outermost electron shell is filled.

How to determine if a bond is covalent, metallic covalent, or ionic? Use the electronegativity constants on the backside of your Periodic Table of Elements (small green number).

Example: What type of bond is CO? 1.What is the electronegativity of C? C= What is the electronegativity of O? O= Subtract the difference between the two constants and round to the nearest tenth. ( Oxygen) 3.50 – (Carbon) 2.55 = 0.95 or 1.0

4. Use the Percent Ionic Character table located on the handout called “Electronegativity” 1.0 = 22%. This is less than 50% Ionic Character, so CO is formed by a COVALENT BOND.

Example: What type of bond is PbCr 2 1.What is the electronegativity of Pb? Pb = What is the electronegativity of Cr? Cr = Subtract the difference between the two constants and round to the nearest tenth. (Lead) 2.33 – (Chromium)1.66 = 0.67 or 0.7

4. Use the Percent Ionic Character table located on the handout called “Electronegativity” 0.7 = 12%. This is less than 50% Ionic Character, METALLIC COVALENT BOND. 0.7 = 12%. This is less than 50% Ionic Character, and both elements forming the bond are metals, therefore the bond is a METALLIC COVALENT BOND.

Lets prove that NaCl is formed by an Ionic Bond. Calculate the Percent Ionic Character for NaCl. Na= 0.93Cl= – 0.93 = 2.23 or = 70% NaCl is formed by an Ionic Bond because its greater than 50%.