4.5.1 - Writing Simple Formulas for Ionic and Covalent Compounds

Alright class, today we will learn about writing chemical formulas for ionic compounds. Who can tell me what an ionic compound is?

Great job, Student_1! Ionic compounds are indeed formed by metals donating electrons to non-metals. This electron transfer creates positive and negative ions. Can someone tell me what we call these ions?

Exactly! Remember, cations are like cats climbing trees— they go up! Anions are like animals running away to avoid the cats—they go down. Now, let's look at how to write these formulas.

Good question! First, we write the symbol for the metal ion, then the non-metal ion. We write their charges as superscripts and follow the criss-cross method for the subscripts. Let’s practice with Sodium Chloride!

That's correct! Na⁺ and Cl⁻ balance each other out as they are equal, resulting in NaCl. To summarize, when writing ionic formulas, make sure to write the metal first and balance the charges.

Now that we understand the concept, let's go through the steps. Who can summarize what we do first?

Perfect! Next, what do we do?

Right again! Now we add the charge as a superscript. Let’s apply this to Magnesium Oxide, which has Mg²⁺ and O²⁻.

Exactly! But we simplify that to MgO because the total charge is neutral. Always simplify your formulas. Any questions?

Now let’s shift gears to covalent compounds. What do you remember about how covalent compounds are formed?

Correct! Sharing electrons results in discrete molecules. Let's look at how we write formulas for these compounds.

No, we don’t use charges. Instead, we count the number of atoms of each element present in the molecule. Let’s take Water (H₂O) as an example.

Exactly! Always make sure to count accurately. To summarize: for covalent compounds, use subscripts to represent the number of each type of atom.

Next, let’s discuss how to count atoms correctly in a formula. Who can explain how subscripts work?

Exactly! If there’s no subscript, it means there’s just one atom of that element. What about when we see parentheses?

Correct! If there's a subscript outside the parentheses, it multiplies the atoms inside. For instance, in Mg(OH)₂, how many oxygen and hydrogen are there?

Yes! Always apply the subscript to everything inside the parentheses. Great job, everyone!

Now, let’s practice! What’s the formula for Carbon Dioxide?

Great! And how about Methane?

Exactly! I encourage you all to try writing a few more formulas at home. Remember to practice counting the atoms, especially with more complex formulas!

I’m glad to hear that! Remember, practice makes perfect!