Name:______________________________________________ Block:___________ Date:___________
Introduction to Chemical Bonding
Atoms, molecules, and compounds are essential to life. Without these more complex groupings of
atoms like glucose (C6H12O6), water (H2O), and oxygen (O2), life wouldn’t be possible. What makes
these molecules possible? Bonding! But what is bonding and how does it occur?
1. Bonding is the way atoms stick together by stealing or sharing electrons. Which electrons are
doing the bonding? Where are these electrons located?
Valence electrons on the outermost shell
2. Why do atoms bond? An atom’s goal in life is to have 8 electrons on its outer shell. This rule is
called the Octet Rule. It states that atoms tend to gain, lose or share electrons so they have
eight electrons in their valence shell. Not all atoms have a full valence shell (8 valence
electrons). The only group with a full outer shell is the Noble Gas family (group 18 nonmetals).
All the other elements on the periodic table have less than 8 valence electrons. In the last unit,
you learned how to use the periodic table to determine the number of valence electrons an
atom has. Let’s practice! How many valence electrons do the following elements have?
Draw the Lewis dot structure next to each element
___2__Calcium
___2___Beryllium
___7___Chlorine
___8___Xenon
___1___Rubidium
___6___Tellurium
___5___Nitrogen
___4___Tin
___3___Aluminum
___1___Hydrogen
___1___Sodium
___6___Oxygen
Are these elements happy? Do they have a full valence shell? No, they need to do something to fill
their outer shell, so they will bond!
3. Let’s look at oxygen (O). Oxygen has an atomic number of 8 and it has 2 energy levels. Its first
energy level is filled with 2 electrons, which leaves 6 on its outer shell. Therefore, oxygen has
6 valence electrons. For oxygen to be happy and full, it needs to have 8 valence electrons, so
oxygen needs __2____ more valence electrons. Because it needs __2___ more valence
electrons, oxygen will make 2 bonds. Knowing that this is oxygen’s goal, explain why water’s
molecular formula is H2O. Draw the Lewis dot structure of this molecule (use 2 colors)
Oxygen’s outer electron shell has 6 valence electrons and it forms covalent bonds with 2
Hydrogen atoms, which have 1 valence electron each. This gives each atom a complete
valence shell; 8 for Oxygen and 2 for Hydrogen
4. So, we know that due to oxygen needing 2 more valence electrons it will make 2 bonds, but
why doesn’t hydrogen just give up the electron? Why do they link?
Both Hydrogen and Oxygen are non-metals which form covalent bonds, which share the
electrons
Name:______________________________________________ Block:___________ Date:___________
5. This bond between hydrogen and oxygen is a covalent bond. A covalent bond is
Between two non-metals who share the electrons
6. This means that the electrons are shared around both of the atoms. Hydrogen still needs that
electron, so it shares it with oxygen so that they both can have a full outer shell. Some
examples of covalent molecules are:
CO2
O2
H2
HNO3
H2SO4
HCl
7. What do you notice about all of the elements in these molecules?
All are non-metals
8. So, covalent bonds usually occur between _non___--__metals__. But what about when a
metal and a non-metal bond? What happens to the electrons in that situation?
9. Bonding between a metal and a non-metal is slightly different than bonding between 2 nonmetals. When a metal and non-metal bond, the non-metal steals the electron(s) from the
metal. This is ionic bonding. Ionic bonding is
Always between a metal and non-metal. The non-metal takes the electron from the metal; this
forms two ions which are then attracted to each other, forming an ionic bond.
10. This means that atoms in an ionic bond are gaining and losing electrons. This exchange of
electrons creates ions: the metal forms a positive ion when losing an electron and the
non-metal forms a negative ion when it gains an electron.
11. Let’s look at NaCl or table salt. Is this an ionic bond? How do you know? Which element is the
metal? Which element is the non-metal? The bond is ionic because it is between a metal
and a non-metal. Na is the metal and Cl is the non-metal
12. When sodium (Na) bonds with chlorine (Cl), they exchange electrons. The sodium has 1
valence electron and the chlorine has 7. The chlorine needs one more electron to fill its
valence shell so it steals the valence electron from sodium. Now, chlorine has one more
electron than protons, therefore, it has a charge of -1. The sodium, on the other hand, now has
one less electron than protons and it has a charge of +1. In covalent bonds, the atoms shared
electrons and so that acts like a line connecting the two. In an ionic bond, that line doesn’t
exist. So what is keeping the atoms together? The atoms in NaCl form a Na+ ion and a Clion when Chlorine takes Sodium’s lone valence electron. These two oppositely charged
ions are attracted to each other and form the ionic bond.
13. What influences the types of bonds atoms will form?
If the elements in the compound are all non-metals, covalent bonds are formed and if
the elements are metals and non-metals, ionic bonds are formed
Name:______________________________________________ Block:___________ Date:___________
Identify the following compounds as ionic or covalent and draw the Lewis dot structure for each
compound.
1. Lithium Chloride (LiCl)___ionic______
2. Sulfur Trioxide (SO3)____covalent_
3. Dinitrogen Oxide (N2O)__covalent___
4. Ammonia (NH3) ___covalent__
5. Silver Chloride (AgCl)__ionic_______
6. Carbon Dioxide (CO2) __covalent____
7. Lead Iodide (PbI2)___ionic________
8. Potassium Fluoride (KF) ___ionic_______
9. Iron (II) Oxide (FeO2)___ionic_______
10. Carbon tetrachloride (CCL4)__covalent_____
11. Potassium Nitrate (KNO3)___ionic________
12. Copper (II) Sulfate (CuSO4)___ionic_______
Answer the following questions
1. How many lithium (Li) atoms are needed to completely fill oxygen’s (O) valence shell?
two
2. How many chlorine (Cl) atoms are needed to completely fill carbon’s (C) valence shell?
four
3. How many potassium (K) atoms are needed to completely fill bromine’s (Br) valence
shell?
one
4. Which of the above examples are examples of ionic bonds? Which are covalent?
Number 1 and 3 are ionic, 2 is covalent
5. Write the molecular formula for magnesium oxide.
MgO
Challenge: Write the molecular formula for dihydrogen monoxide. H2O