*This lesson is expected to require two periods to complete*
Part 1: Differences between ionic and covalent bonding
- The differences between ionic and covalent bonds will be introduced:
Explain that ionic bonds consist of an “agreement” between an electron donor and an electron
taker. An electron is “exchanged” in an ionic bond. Covalent bonds consist of two or more
elements sharing valence electrons. Neither element is taking or giving an electron; rather, they
are both contributing single valence electrons to form stable pairs. Highlight the above
difference – ionic bonding involves electron giving and taking (the cation is “emptying” an
electron shell while the anion is “filling” one), whereas covalent bonding involves electron
sharing to form stable electron pairs.
Also discuss the fact that ionic bonds form between metals and non-metals whereas as covalent
bonds form between non-metals. The concept of double and triple bonds should be introduced
(ionic bonds are singular; covalent bonds can be singular or multiple – think of CO2)
Illustrate the above explanation on the white board.
Part 2: Magnesium metal and hydrochloric acid
Instructor demonstration:
- Add 5 mL of HCl to a small beaker.
- Add a 2 cm by 1 cm strip of magnesium to the beaker.
- Cover the beaker for 15 seconds.
- Light a regular match. Use the match to light a burning splint.
- Remove the cover from the beaker and place the match over the opening.
Use this as an opportunity to explain what has occurred. The HCl and Mg(s) have reacted to form H2(g).
When this gas is lit, the burning O2 and H2 react to form the H2O, a polar covalent compound.
Part 3: Linking the Bohr model to ionic and covalent bonding
- Using the white board, link the Bohr model to ionic and covalent bonding:
Complete the Bohr model diagrams for Na and Cl. Next, write the Bohr model diagrams for Na+
and Cl- (these are to be placed directly below the Na and Cl Bohr models – draw an arrow
between them to show the connection). Third, explain what the difference between the two
sets of models is. Finally, connect the Bohr models for Na+ and Cl- in an ionic bond.
Next, the instructor will repeat the above procedure for CH4 (the ion stage is to be omitted, as
no ions are involved in the formation of covalent bonds). Write out the Bohr diagrams for
carbon and hydrogen. Next, connect the two in the manner of a covalent bond (the shells will
overlap). Note the distinction between ionic and covalent bonds in terms of the placement of
electrons both between the two elements and within the energy shells of each respective atom.
The ionic bond involved the TRANSFER of an electron from sodium to chloride, whereas the
covalent bond involved the SHARING of VALENCE electrons (both atoms “gain” an electron, and
both elements are non-metals – metals can ONLY give away electrons, as accepting electrons is
energetically unfavourable).
- Write down 6 questions on the board. The questions will consist of a list of ions arranged in pairs.
The students will draw the Bohr model for the ions, linking the two models together to form an ionic
bond. The students will be given 10-15 minutes to complete the questions. The questions will be
corrected in class.
Part 4: Covalent bonding nomenclature
- The instructor will introduce the Greek prefix naming convention. Highlight the similarities between
the naming conventions for ionic and covalent compounds. Explain that the only true differences are as
follows:
Greek prefixes are used when naming covalent molecules. The prefixes are used for both the
first and second elements listed. *Exception – the mono prefix is never used to the first listed
element*
The –ide suffix is still applied to the second element listed. The first element does not receive
the suffix despite also being a non-metal.
Both elements comprising the compound are non-metals (found to the right of the staircase on
the periodic table).
- Students will complete a covalent bonding nomenclature practice sheet.
Part 5: Covalent bonding formula writing
- This section will be short, as writing the formula for covalent compounds is significantly easier than
writing the formula for ionic compounds.
- Demonstrate the process using multiple examples and students feedback.
- Students will complete a covalent bonding formula writing practice sheet.
Part 6: Covalent bonding nomenclature and formula writing quiz
Part 7: Nomenclature review
- Distribute the naming conventions cheat sheet.
- Recap the naming conventions.
- Students will work on a mixed ionic and covalent nomenclature and formula writing sheet.