Lewis Structures and Hybridization Quiz

The valence electrons in an atom are the electrons in the outer most principal shel

Lewis structures use Lewis symbols to show valence electrons of main-group elements as dots surrounding the symbol of the atom.

Ionic bonds are formed by transfer of electrons from a metal to a non-metal. Therefore, the Lewis structure for these compounds is drawn by moving the electrons from metal to non-metal.

Covalent compounds are formed by sharing electrons. Therefore, the Lewis structures for these compounds are drawn by allowing neighboring atoms to share some of their valence electrons.

Ionic bonds are formed by transfer of electrons from a metal to a non-metal. Therefore, the Lewis structure for these compounds is drawn by moving the electrons from metal to non-metal.

Covalent compounds are formed by sharing electrons. Therefore, the Lewis structures for these compounds are drawn by allowing neighboring atoms to share some of their valence electrons.

The electrons that are shared between the atoms are called bonding pair electrons, while those that are only on one atom are called lone pair electrons.

The electrons that are shared between the atoms are called bonding pair electrons, while those that are only on one atom are called lone pair electrons.

The bonding pair electrons can often represented as dash lines, to emphasize that they are chemical bonds, but the lone pair electrons are always displayed as dots.

The bonding pair electrons can often represented as dash lines, to emphasize that they are chemical bonds, but the lone pair electrons are always displayed as dots.

The Lewis model also explains why halogens are diatomic.

The Lewis model also allows atoms to share more than one pair of electrons to achieve octet.

When writing Lewis structures, it might be possible to write more than one good (valid) structure for some molecules.

equivalent structures are called resonance structures

The structure is intermediate between two structures.

The Lewis structure of a molecule, in combination with valence shell electron pair repulsion (VSEPR) theory, can be used to predict the shape of a molecule.

The VSEPR theory is based on the idea that electron groups around the central atom of a molecule repel each other. The repulsion between these electron groups determine the shape of the molecule.

Electron groups are defined as: lone pairs, single bonds or multiple bonds.

For example, CO2, with the Lewis structure shown below, has two electron groups (two double bonds) around the central atom. The repulsion between these groups produce a linear shape for the molecule with bond angle of 180.

As another example, the molecule H2CO, with Lewis structure shown below, has 3 electron groups around the central atom. The repulsion between these groups produce a trigonal planar geometry with a bond angle of 120.

the shape produced by the electrons is called electron geometry.

When one of more lone pairs are around the central atom, the shape of the molecule as it appears to us is different than the electron geometry, and is referred to as molecular geometry.

The ability of an element to attract electrons within a covalent molecule is called electronegativity.

For example, oxygen is more electronegative than hydrogen. This means that on the average, the shared electrons are more likely to be found near the oxygen atom than near the hydrogen atom.

oxygen is more electronegative than hydrogen. This means that on the average, the shared electrons are more likely to be found near the oxygen atom than near the hydrogen atom.

The result of this uneven sharing of electrons in the O-H bond is the separation of charge in the bond, called dipole moment. Covanlent bonds that have dipole moment are called polar covalent bonds.

Covanlent bonds that have dipole moment are called polar covalent bonds.

The dipole moment in a bond is sometimes shown with a vector representation, where the vector points to the direction of the atom with the partial negative charge.

The magnitude of the dipole moment, and therefore the degree of polarity of the bond, depend on the difference in electronegativity between the two elements forming the bond and the bond length.

For a fixed bond length, the greater the electronegativity difference, the greater the dipole moment and the more polar the bond.

Note that electronegativity increases across a period and decreases down a group.

If two elements with nearly identical electronegativities form a covalent bond, they share the electron equally, and there is little or no dipole moment. These bonds are called non-polar covalent bonds.

For example, Cl2 molecule, composed of 2 chlorine atoms (with same
electronegativities) form such a bond.

When two elements with intermediate electronegativity difference form a bond, such as two nonmetals, the electrons are shared unequally and there is an intermediate dipole moment. These bonds are called
polar covalent. H and F form such a bond.

If there is a large electronegativity difference between two elements forming a bond, such as a metal and nonmetal, the electron is transferred and a there is a large dipole moment. These bonds are called ionic.
Sodium and chlorine form such a bond.

Many molecules with polar bonds become non-polar, because their bond polarities cancel out one another due to their shapes.

For diatomic molecules, the polarity of the molecule can easily be determined from the polarity of the bond, since the bond forms the molecule. Therefore, diatomic molecules with non-polar bonds are non-polar, and those with polar bonds are polar.

For molecules with more than two atoms, it is more difficult to distinguish between the polar and non-polar molecules, because two or more polar bonds may cancel each other.

For example, consider the carbon dioxide molecule: each C=O bond is polar because the difference in electronegativity between oxygen and carbon is 0.89. However, due to the linear shape of the molecule, the dipole moment of each bond is cancelled since they are in opposite directions, leading to a non-polar molecule.

Water, on the other hand, also has two polar O-H bonds, since the electronegativity difference between hydrogen and oxygen is 1.24. However, the bent shape of the water molecule does not allow the two dipole moments of the bonds to cancel one another. As a result water is a polar molecule.

Molecules with symmetrical shapes such as linear, trigonal planar and tetrahedral, allow for cancellation of dipole moments and are non-polar when all atoms around the central atom are the same.

Molecules with unsymmetrical shapes such as bent and pyramidal do not allow for cancellation of dipole moments are always polar.

to determine if a molecule is polar:
First determine whether the molecule contains polar bonds. A bond is polar if the two atoms forming the bond have different electronegativities. If no polar bonds exist, the molecule is non-polar.Next determine if the polarity of the bonds cancel one another because of the shape. Use VSEPR model to determine the shape of the molecule and then evaluate if the polarity of the bonds can be cancelled due to the shape.

to determine if a molecule is polar:
First determine whether the molecule contains polar bonds. A bond is polar if the two atoms forming the bond have different electronegativities. If no polar bonds exist, the molecule is non-polar.Next determine if the polarity of the bonds cancel one another because of the shape. Use VSEPR model to determine the shape of the molecule and then evaluate if the polarity of the bonds can be cancelled due to the shape.