When we study chemical bonding, why are we concerned mostly with the valence ele

Question

When we study chemical bonding, why are we concerned mostly with the valence electrons of the atoms? What does a Lewis dot symbol consist of? Use Lewis dot symbols to show the formation of aluminum oxide (AI203). Explain how we are able to measure lattice energy if it cannot be measured directly. What type of electrons are shown in a Lewis structure? Explain how to use element electronegativities to determine whether a bond is ionic, polar covalent, or non polar covalent. Why do some compounds have more than one Lewis structure to represent their configuration - a resonance structure? Show this concept for the benzene molecule. All3, aluminum triiodide is an example of an incomplete octet molecule. Draw the Lewis structure for it. Describe bond enthalpy and how this measure is useful. Compare single, double, and triple bonds in a molecule. Give an example for each. For the same bonding atoms, how does the bond length change from single bond to triple bond?

Explanation / Answer

Dear Student,

1. In chemical bonding, we are mostly concerned with valence elctrons of atoms because the presence of valence electrons can determine the element's chemical properties and whether it may bond with other elements.

A valence electron is an electron that is associated with an atom, and that can participate in the formation of a chemical bond.

For example, in a single covalent bond, both atoms in the bond contribute one valence electron in order to form a shared pair.

For a main group element, a valence electron can only be in the outermost electron shell.

In a transition metal, a valence electron can also be in an inner shell.

Therefore, in chemical bonding we are concerned with valence electrons of atoms.

2. Lewis dot symbol consist of excess electrons that forms lone pairs.

3. Lewis dot symbol to show formation of Al2O3 is as follows:

4. To measure lattice energy there are two different ways

1. Hess's Law (Experimental Values)

2. physics style calculations working out how much energy would be released (Theoretical Values)

5. The type of electrons shown in Lewis Structure are valence electrons that form lone pairs which are represented as pair of dots and are placed next to the atom.

6.

Electro-negativity is defined as the ability of an atom in a particular molecule to attract electrons to it

A general rule for predicting the type of bond based upon electro-negativity differences:

If the electro - negativities are equal (i.e. if the electro-negativity difference is 0), the bond is non-polar covalent (the one in which the electrons are shared equally between two atoms).

If the difference in electro-negativities between the two atoms is greater than 0, but less than 2.0, the bond is polar covalent (the one in which one atom has a greater attraction for the electrons than the other atom.)

If the difference in electro-negativities between the two atoms is 2.0, or greater, the bond is ionic (where relative attraction is great enough).

7. There are several ways to draw the Benzene (C6H6 )Lewis structure.

The most common is to form a ring with the six carbon atoms.

In this you will notice that there are not many hydrogen atoms in the structure.

You will need to form alternating double bonds in order to fill the outer shells of the atoms and only use 30 valence electrons.

Therefore, there are more than one lewis structure for Benzene ring in order to fill the outer shells of the atoms.

8. The octet rule states that atoms with an atomic number below 20 tend to combine so that they each have eight electrons in their valence shells, which gives them the same electronic configuration as a noble gas.

The two elements that most commonly fail to complete an octet are boron and aluminum; they both readily form compounds in which they have six valence electrons, rather than the usual eight predicted by the octet rule.

Lewis structure of Alluminium Triiodide is as follows:

9. Bond enthalpy (H) is the measure of bond strength in a chemical bond.

IUPAC defines bond energy as the average value of the gas-phase bond dissociation energies (usually at a temperature of 298 K) for all bonds of the same type within the same chemical species.

For example, the carbon-hydrogen bond energy in methane H(C–H) is the enthalpy change involved with breaking up one molecule of methane into a carbon atom and 4 hydrogen radicals, divided by 4.

10. A single bond is when two electrons--one pair of electrons--are shared between two atoms. It is depicted by a single line between the two atoms. Although this form of bond is weaker and has a smaller density than a double bond and a triple bond, it is the most stable because it has a lower level of reactivity meaning less vulnerability in losing electrons to atoms that want to steal electrons. HCl is a example of single bond with a bond length 0.127 nm.

A Double bond is when two atoms share two pairs of electrons with each other. It is depicted by two horizontal lines between two atoms in a molecule. This type of bond is much stronger than a single bond, but less stable; this is due to its greater amount of reactivity compared to a single bond. CO2 is an example of double bond with a bond length 1.16 nm.

A Triple bond is when three pairs of electrons are shared between two atoms in a molecule. It is the least stable out of the three general types of covalent bonds. Acetylene is an example of triple bond with a bond length 106.4 nm.

Therefore, In a molecule as the number of electrons shared between two atoms are increased, there is a increase in the bond order, increase in the strength of the bond, and decrease in the distance between nuclei (bond length).

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