Question About Ionic Bonds

[MissionStanford]

We say that ionic compounds have high melting points due to the fact that ionic bonds are strong. But, take NaCl for example. Melting solid NaCl means taking tightly packed NaCl molecules and separating the MOLECULES, not Na+ and Cl-. So when we say that it is the strong ionic bonds that make the melting point high, are we really referring to ionic bonds between NaCl MOLECULES in a lattice of NaCl molecules? As opposed to referring to the ionic bond between Na+ and Cl- in one molecule of NaCl.

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[ChemTutor]

NaCl is ionic, so we should assume that NaCl molecules do not exist.

NaCl lattice

 

[dsoz]

Molten (liquid) NaCl conducts electricity. Therefore it is assumed to be made up of SEPARATE ions of Na+ and Cl-. Melting it is the energy that is required to break up the ionic bonds between the ions. Since there is a lattice of ions, there is no such thing as a molecule of NaCl.

dsoz

 

[MissionStanford]

Molten (liquid) NaCl conducts electricity. Therefore it is assumed to be made up of SEPARATE ions of Na+ and Cl-. Melting it is the energy that is required to break up the ionic bonds between the ions. Since there is a lattice of ions, there is no such thing as a molecule of NaCl.

dsoz

So basically there are no NaCl "molecules" but rather a lattice, which is solid and consists of lots of Na+ and Cl- ions, and the separation of these ions from this strongly bonded network causes melting into a solid?

 

[DNA]

We say that ionic compounds have high melting points due to the fact that ionic bonds are strong. But, take NaCl for example. Melting solid NaCl means taking tightly packed NaCl molecules and separating the MOLECULES, not Na+ and Cl-. So when we say that it is the strong ionic bonds that make the melting point high, are we really referring to ionic bonds between NaCl MOLECULES in a lattice of NaCl molecules? As opposed to referring to the ionic bond between Na+ and Cl- in one molecule of NaCl.

You should really review your understanding of molecules vs. compounds and ionic vs. covalent bonds before you really dive into this topic. You'll understand it a whole lot better.

A molecule by definition is series of elements connected by covalent bonds. In order for two elements to be covalently bonded (share electrons), the difference in their electronegativies cannot be too great. However, if the electronegativies ARE distinct enough as is the case in NaCl, we call that an Ionic Compound. An Ionic Compound is essentially a series of elements that are bonded by charges. In otherwords, electrons are no longer shared, but essentially yanked off the less electronegative atom (Na) and attached to the more electronegative atom (Cl).

There is an important distinction here. When you begin analyzing why say, the boiling point of NaCl is considerably higher than Water (H2O) for example, you have to analyze the bonds being made. NaCl is a lattice of charges. The positive charge of Sodium (Na) is strongly attracted to the negative charge of Chlorine (Cl). Ignoring for a moment the covalent bonds WITHIN a water molecule, each water molecular is connected to one another via a series of Van der Waals forces (look them up). These forces collectively are still considerably weaker than Ionic Bonds.

HOWEVER, if we were actually comparing the strength of an Ionic Bond vs. Covalent Bond, we would find they are relatively similar. Infact, you'll find that in a Network Solid (ie. Diamond), each carbon atom is connected entirely by covalent bonds, and therefore the compound as a whole has similar boiling points to most Ionic Compounds. But when we are referring to the boiling point of molecules, we are strictly looking at the Van der Waals forces. Likewise, for Ionic Compounds, we are looking at the Ionic Bonds.

In short, here's what you need to realize:
Ionic Bonds ~ Covalent Bonds >>>>>> Van der Waal Forces

 

[DNA]

So basically there are no NaCl "molecules" but rather a lattice, which is solid and consists of lots of Na+ and Cl- ions, and the separation of these ions from this strongly bonded network causes melting into a solid?

And stop calling NaCl a molecule. It's a compound 🙂. A very important concept you should understand, hopefully with my explanation above.

 

[MissionStanford]

You should really review your understanding of molecules vs. compounds and ionic vs. covalent bonds before you really dive into this topic. You'll understand it a whole lot better.

A molecule by definition is series of elements connected by covalent bonds. In order for two elements to be covalently bonded (share electrons), the difference in their electronegativies cannot be too great. However, if the electronegativies ARE distinct enough as is the case in NaCl, we call that an Ionic Compound. An Ionic Compound is essentially a series of elements that are bonded by charges. In otherwords, electrons are no longer shared, but essentially yanked off the less electronegative atom (Na) and attached to the more electronegative atom (Cl).

There is an important distinction here. When you begin analyzing why say, the boiling point of NaCl is considerably higher than Water (H2O) for example, you have to analyze the bonds being made. NaCl is a lattice of charges. The positive charge of Sodium (Na) is strongly attracted to the negative charge of Chlorine (Cl). Ignoring for a moment the covalent bonds WITHIN a water molecule, each water molecular is connected to one another via a series of Van der Waals forces (look them up). These forces collectively are still considerably weaker than Ionic Bonds.

HOWEVER, if we were actually comparing the strength of an Ionic Bond vs. Covalent Bond, we would find they are relatively similar. Infact, you'll find that in a Network Solid (ie. Diamond), each carbon atom is connected entirely by covalent bonds, and therefore the compound as a whole has similar boiling points to most Ionic Compounds. But when we are referring to the boiling point of molecules, we are strictly looking at the Van der Waals forces. Likewise, for Ionic Compounds, we are looking at the Ionic Bonds.

In short, here's what you need to realize:
Ionic Bonds ~ Covalent Bonds >>>>>> Van der Waal Forces

Great explanation. Thank you.🙂

 

[dsoz]

You should really review your understanding of molecules vs. compounds and ionic vs. covalent bonds before you really dive into this topic. You'll understand it a whole lot better.

A molecule by definition is series of elements connected by covalent bonds. In order for two elements to be covalently bonded (share electrons), the difference in their electronegativies cannot be too great. However, if the electronegativies ARE distinct enough as is the case in NaCl, we call that an Ionic Compound. An Ionic Compound is essentially a series of elements that are bonded by charges. In otherwords, electrons are no longer shared, but essentially yanked off the less electronegative atom (Na) and attached to the more electronegative atom (Cl).

There is an important distinction here. When you begin analyzing why say, the boiling point of NaCl is considerably higher than Water (H2O) for example, you have to analyze the bonds being made. NaCl is a lattice of charges. The positive charge of Sodium (Na) is strongly attracted to the negative charge of Chlorine (Cl). Ignoring for a moment the covalent bonds WITHIN a water molecule, each water molecular is connected to one another via a series of Van der Waals forces (look them up). These forces collectively are still considerably weaker than Ionic Bonds.

HOWEVER, if we were actually comparing the strength of an Ionic Bond vs. Covalent Bond, we would find they are relatively similar. Infact, you'll find that in a Network Solid (ie. Diamond), each carbon atom is connected entirely by covalent bonds, and therefore the compound as a whole has similar boiling points to most Ionic Compounds. But when we are referring to the boiling point of molecules, we are strictly looking at the Van der Waals forces. Likewise, for Ionic Compounds, we are looking at the Ionic Bonds.

In short, here's what you need to realize:
Ionic Bonds ~ Covalent Bonds >>>>>> Van der Waal Forces

not quite....

Water molecules are held together by three distinct forces. 1) Van der Waals. 2) dipole-dipole interactions between the permanent polarity of the O-H bonds (Oxygen is partially negative and hydrogen partially positive due to difference in electronegativity). and 3) hydrogen bonding.

Things like carbon dioxide or neon gas are only attracted by Van der Waals forces. The weak intermolecular forces tend to show up in substances that are gasses (at room temperature and pressure). medium strength forces are liquids and strong interactive forces are solids (gross generalization and there are as many exceptions as there are rules it seems).

Read up on intermolecular forces.

dsoz

 

[DNA]

not quite....

Water molecules are held together by three distinct forces. 1) Van der Waals. 2) dipole-dipole interactions between the permanent polarity of the O-H bonds (Oxygen is partially negative and hydrogen partially positive due to difference in electronegativity). and 3) hydrogen bonding.

Things like carbon dioxide or neon gas are only attracted by Van der Waals forces. The weak intermolecular forces tend to show up in substances that are gasses (at room temperature and pressure). medium strength forces are liquids and strong interactive forces are solids (gross generalization and there are as many exceptions as there are rules it seems).

Read up on intermolecular forces.

dsoz

"Van der Waal forces" is a collective term inclusive of all the forms of intermolecular bonding: Hydrogen-Bonding, Dipole-Dipole, and London Dispersion forces. In some textbooks, they use the term Van der Waals interchangeable with London Dispersion forces.

Also, the example I gave was Water. Had I said Neon Gas, Carbon Dioxide, or any other non-polar molecular, I would have felt the need to clarify that only London Dispersion forces were acting on those molecules.

 

[ChemTutor]

"Van der Waal forces" is a collective term inclusive of all the forms of intermolecular bonding: Hydrogen-Bonding, Dipole-Dipole, and London Dispersion forces. In some textbooks, they use the term Van der Waals interchangeable with London Dispersion forces.

Also, the example I gave was Water. Had I said Neon Gas, Carbon Dioxide, or any other non-polar molecular, I would have felt the need to clarify that only London Dispersion forces were acting on those molecules.

WIKI: the van der Waals force (or van der Waals interaction), named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds, the hydrogen bonds, or the electrostatic interaction of ions with one another or with neutral molecules.[1]

 

[DNA]

WIKI: the van der Waals force (or van der Waals interaction), named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds, the hydrogen bonds, or the electrostatic interaction of ions with one another or with neutral molecules.[1]

Like I said before, the term Van der Waal is open to interpretation:

Intermolecular Forces have historically also been called Van der Waal forces which is really the correct interpretation - meaning it covers all the forces between molecules. However, be warned, many books (and questions) equate Van der Waal forces with ONLY dispersion forces. Check out Wikipedia for Van der Waals forces - you’ll see there under the definition section that the term can be meant one way or another. Best to know the authors intent as they say. Unfortunately our history is steeped in tradition and the term on Quest usually refers to just dispersion forces. We’ll try to stick with this concept on the exam. In other classes (biology, etc...) you might have to adjust your thinking on this term.

SOURCE: http://mccord.cm.utexas.edu/courses/fall2012/ch301/unit3-mccord.php