Basic Chemistry Stuff(2)

[kingwinner]

I am taking an Earth Science course now and currently reviewing some basic chemistry knowledge needed for further study on earh mineral and rocks. But I haven't touched chemistry for almost 2 years that I start to forget things, can someone help and clarify some basic chemistry stuff? I would appreciate!

1) The smallest unit of a covalent compound is molecule. But what is a formula unit? Is it the smallest unit of an ionic compound that still retains its chemical and physical properties?

2) Why is a solution considered to be a mixture instead of a compound? Is dissolving a chemical reaction?

3) For examle, predict the chemical formula of carbon chemically combining with oxygen, C2O4 is obtained which must be reduced to its lowest ratio, CO2, but why something such as C6H12O6 cannot be reduced to CH2O? How can I know when a chemical formula is to reduce and when not to?

[Jay-qu]

Originally Posted by kingwinner

1) The smallest unit of a covalent compound is molecule. But what is a formula unit? Is it the smallest unit of an ionic compound that still retains its chemical and physical properties?

2) Why is a solution considered to be a mixture instead of a compound? Is dissolving a chemical reaction?

3) For examle, predict the chemical formula of carbon chemically combining with oxygen, C2O4 is obtained which must be reduced to its lowest ratio, CO2, but why something such as C6H12O6 cannot be reduced to CH2O? How can I know when a chemical formula is to reduce and when not to?

1. no idea what your talking about - please re-phrase

2. When something is dissolved in a solution it is a physical change no reaction takes place. but that is not to say that something cant react with water when it is dissolved in water

3. you are talking about empirical formula which you use mostly when dealing with polymers and other large molecules

[kingwinner]

Originally Posted by Jay-qu

1. no idea what your talking about - please re-phrase

2. When something is dissolved in a solution it is a physical change no reaction takes place. but that is not to say that something cant react with water when it is dissolved in water

3. you are talking about empirical formula which you use mostly when dealing with polymers and other large molecules

1) An atom is the smallest unit of an element that still retains its chemical and physical properties.
A molecule is the smallest unit of a covalent compound that still retains its chemical and physical properties.
A ________ is the smallest unit of an ionic compound that still retains its chemical and physical properties.
Would the answer to the blank be "formula unit", since ionic bonding doesn't form a molecule...?!

2) Say you dissolve MgCl2:
MgCl2 -> Mg(2+) + 2Cl(-)
New substance is formed, why still consider the solution as a mixture in which no chemical reaction occurs?

3) Say, when you are asked to draw the Lewis dot diagram for the compound that would form and write its chemical formula at the end:
a) C and O
b) Mg and O

The chemical formulas are CO2, MgO, not C2O4 and Mg2O2, right? You always reduce to its lowest ratios when writing chemical formulas?

[Jay-qu]

Originally Posted by kingwinner

1) An atom is the smallest unit of an element that still retains its chemical and physical properties.
A molecule is the smallest unit of a covalent compound that still retains its chemical and physical properties.
A ________ is the smallest unit of an ionic compound that still retains its chemical and physical properties.
Would the answer to the blank be "formula unit", since ionic bonding doesn't form a molecule...?!

2) Say you dissolve MgCl2:
MgCl2 -> Mg(2+) + 2Cl(-)
New substance is formed, why still consider the solution as a mixture in which no chemical reaction occurs?

3) Say, when you are asked to draw the Lewis dot diagram for the compound that would form and write its chemical formula at the end:
a) C and O
b) Mg and O

The chemical formulas are CO2, MgO, not C2O4 and Mg2O2, right? You always reduce to its lowest ratios when writing chemical formulas?

1. an ion is the smallest unit when in solution - otherwise im not sure because ions normally form salt crystals that are basically a big molecule except for breakeges in the bonding from cracks

2. the magnesium oxide goes from solid to aqueous this is a physical change - although it changes the properties of the solution no reaction takes place.

3. that is because C2O4 doesnt form when you react carbon and oxygen - it may be possible under certain conditions but for all intents and purposes CO2 forms and the same goes for MgO

[kingwinner]

Originally Posted by Jay-qu

1. an ion is the smallest unit when in solution - otherwise im not sure because ions normally form salt crystals that are basically a big molecule except for breakeges in the bonding from cracks

2. the magnesium oxide goes from solid to aqueous this is a physical change - although it changes the properties of the solution no reaction takes place.

3. that is because C2O4 doesnt form when you react carbon and oxygen - it may be possible under certain conditions but for all intents and purposes CO2 forms and the same goes for MgO

3) Then how can I know when it is valid to reduce to chemical formula to its lowest ratio (e.g. Mg2O2 becomes MgO) and when not to (such as C6H12O6) by simply looking at the formula?

[Jay-qu]

that is because the formula doesnt hold all the information about the substance. In the case of C6H12O6 - that is one glucose molecule, so unless asked for the empirical formula of glucose(unlikely question) you quote the full formula. It is just a matter of knowing your chemistry... sorry I cant be of more help