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August 20, 2014

Homework Help: chemistry

Posted by Chris on Monday, September 25, 2006 at 7:26pm.

Criticize the following statements.

1. In an ionic compound, the number of cations is always equal to the number of anions. [Is it ok to say 'not always'?]

2. The molecular formula for strontium bromide is SrBr(sub 2) [what's wrong wih this?]

3. The mass number is always equal to the atomic number. [never?]

4. For any ion, the number of electrons is always more than the number of protons. [is always equal to]


Criticize the following statements.

1. In an ionic compound, the number of cations is always equal to the number of anions. [Is it ok to say 'not always'?]
No, the number of cations is not always equal to the number of anions. Sometimes, yes; always, no.

2. The molecular formula for strontium bromide is SrBr(sub 2) [what's wrong wih this?]
Initially I didn't know what was wrong since the formula IS SrBr2; however, after reflecting for some time, I believe that the clue here is that SrBr2 is an ionic compound. Therefore, the ions are in a three dimensional array, or network. Although the RATIO is 1:2, in reality, the molecular formula is Sr(sub x)Br(sub 2x) and we don't know x because that depends upon how large a crystal of SrBr2 we observe. Same thing with NaCl. We write the simplest formula as NaCl but it actually is NaxClx. BTW, I found a reference in my copy of Advanced Inorganic Chemistry (Cotton & Wilkiinson), Fifth edition, that the halides of Sr and others, although existing as ionic compounds, COULD be vaporized as molecular compounds.

3. The mass number is always equal to the atomic number. [never?]
Never is correct.

4. For any ion, the number of electrons is always more than the number of protons. [is always equal to]
No. Electrons are in excess for negative ions, protons are in excess for positive ions. The number of electrons is equal to the number of protons in a neutral element.

how inteligent you are chris

  • chemistry - Ron, Monday, July 15, 2013 at 4:37am

    Thanks!

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