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CHAPTER 5. IONIC COMPOUNDS Mrs. Czyryca. What you already know:. Ionic compounds donate and accept electrons, not share, in order to become stable. Ionic compounds consist of a metal and a nonmetal . An atom that has lost an electron has a positive charge.
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CHAPTER 5 IONIC COMPOUNDS Mrs. Czyryca
What you already know: • Ionic compounds donate and accept electrons, not share, in order to become stable. • Ionic compounds consist of a metal and a nonmetal. • An atom that has lost an electron has a positive charge. • An atom that has gained an electron has a negative charge.
Remember my joke? • Two atoms were walking down the street. Looking all around, one says, “Oh my gosh, I lost an electron!” The other says, “Are you sure?!” The first says, “I’m POSITIVE!”
You should also remember: • When a compound forms and it’s atoms become stable, energy is given off. • And that’s EXOTHERMIC!
We are using a new unit for ionic compounds • Instead of using atoms, molecules, particles, or ions as a unit---we will use • FORMULA UNITS • Formula units are the smallest collection of an ionic compound
For example: • Instead of writing: 6.022 x 1023molecules NaCl • Write: 6.022 x 1023 formula units NaCl
As you can see from the prior slide, KCl doesn’t exist as a molecule. • There are many, many K and Cl atoms bonded into a structure called the CRYSTAL LATTICE. • The gaseous chlorine, Cl2, exists as individual molecules. • The metal, potassium atoms, K, just pile up like oranges at the grocery store.
Let’s look individually at the potassium and chlorine atoms. • K is in group 1 on the periodic table… • So what is it’s charge likely to be once it loses an electron to become stable?
Chlorine is in group 17 • What charge would chlorine have once it gains an electron in order to become stable?
Cations • That’s pronounced “cat” – “ion”
Anions • That’s pronounced “an” – “ion” not ant ion, an’ ion!
We know a positive with a negative =zero • That’s electroneutrality! when the charges equal zero +1 -1 = 0 (can I use a calculator?)
How many cations and anions are present in Mg3(PO4)2? • One more…
Three cations.And two anions- two phosphate polyatomic anions Mg3(PO4)2?
Potassium’s electron configuration: 1s22s22p63s23p64s1 • It loses that electron in the 4s orbital to become stable. • It then has the same electron configuration as a noble gas. VERY STABLE!
ISOELECTRONIC • having the same electron configuration as another element • The potassium ion is isoelectronic with Argon. • 1s22s22p63s23p6
chlorine’s electron configuration: 1s22s22p63s23p5 • It gains an electron in the 3p orbital to become stable. • It then has the same electron configuration as a noble gas. VERY STABLE!
ISOELECTRONIC • having the same electron configuration as another element • The chlorine ion is also isoelectronic with Argon. • 1s22s22p63s23p6
Naming ions (atoms with a charge) • Like any cation, the potassium keeps it’s name and you add the word “ion” to the end.
“Potassium ion” Not too tricky, huh?
Naming ions (atoms with a charge) • Like any anion, the end of chlorine changes to “ide” • and you add the word “ion” to the end.
The charge on the cation Never an option for the anion b/c it only has one possible charge EVER!