In lesson 20 we learned that an ionic compound is composed of positive and negative ions formed when metals and nonmetals combine. We also learned the rule of zero charge. The negative and positive charges must total zero. Sometimes that means you need more of one element than the other so that the charges equal zero. There is a picture below that displays how this works and how to figure out how many atoms of each element you need.
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Practice Problems
2. If you know that you need a totalcharge of 0 then you know if one of your elements has a much higher charge than the other then you need more of the less charged atom.
3A. +1
3B. +3
Lesson 21
In lesson 21 we reinforced the rule of zero charge and learned that the total number of electrons in a compound must equal eight or a multiple of eight. We also learned about noble gas envy. Noble gas envy is the idea that all elements want to be stable like the noble gases and have a full valence electron shell. The elements must form bonds to complete these goals.
Practice Problems
3A. Yes because lithium has a charge of +1 and chlorine has a charge of -1 so they equal zero.
3B. No because lithium has a charge of +1 and chlorine has a charge of -1, but since there are 2 chlorine atoms the bond can't form because it doesn't follow the rule of zero charge.
Lesson 22
Today we learned about polyatomic ions which is a group of atoms with an overall positive or negative charge that are usually anions. There is a picture below that shows examples and names some high frequency polyatomic ions.
Practice Problems
1. A polyatomic ion is an ion that has 2 or more elements
3B. Potassium sulfate
3D. Magnesium carbonate
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