Unit 2

Question 1

Which element exists as a diatomic molecule in its most stable state?

Answer 1

Hydrogen; H, N, O, F, Cl, Br and I are the elements that exist in nature as diatomic molecules. Water isn’t an element; its a compound

Question 2

The transition metals are elements with partially filled

Answer 2

D subshells; In transition metals, d orbitals are being filled.

Question 3

For an isoelectronic series of ions, the ion that is the smallest is always

Answer 3

the ion with the highest atomic number; Isoelectronic ions all have the same number of electrons. However, the one with the highest atomic number will have the largest effective nuclear charge.

Question 4

Increasing electronegativity

Answer 4

Electronegativity generally increases from left to right and from bottom to top of the periodic table.

Question 5

Nonmetals rarely lose electrons in chemical reactions because

Answer 5

their ionization energies are too high; Nonmetals are located in the top right of the periodic table; they tend to have smaller atomic radii and large ionization energies. They also tend to form negative ions so they have larger electron affinities; thes ions are larger than the parent ion

Question 6

Relative strengths

Answer 6

The strength of the coulombic interaction between the two ions is directly proportional to their charges and inversely proportional to their separation. The separation of the ions is determined by their radii. Therefore the strongest interactions will be between small ions and with a high charge.

Question 7

Highest melting point

Answer 7

Highest charge density

Question 8

Lowest lattice energy

Answer 8

Lowest charge densities due to large size

Question 9

Covalent Bonding

Answer 9

Bonding that occurs between elements with similar electronegativities, and with sharing of electrons

Question 10

Highest melting point

Answer 10

Ionic compounds generally have higher melting points than covalent molecules

Question 11

Best conductor of electricity in the pure liquid state (when melted)

Answer 11

Ionic compounds are generally better conductors in the molten state

Question 12

Forms multiple (double or triple) bonds

Answer 12

-Hydrogen can form only one bonds

-Lithium forms ionic bonds rather than covalent bonds

-Both Chlorine and Fluorine need only one more electron to fill their octet and they therefore tend to form only single bonds

-Nitrogen needs 3 more electrons to fill its octet and is therefore tend to form multiple bonds

Question 13

Ionic Bonding

Answer 13

-The complete transfer of valence electron(s) between atoms.

• It is a type of chemical bond that generates two oppositely charged ions.

-In ionic bonds, the metal loses electrons to become a positively charged cation, whereas the nonmetal accepts those electrons to become a negatively charged anion.

-Ionic bonds require an electron donor, often a metal, and an electron acceptor, a nonmetal.

Question 14

Covalent Bonding

Answer 14

• The sharing of electrons between atoms.

-This type of bonding occurs between two atoms of the same element or of elements close to each other in the periodic table.

-This bonding occurs primarily between nonmetals; however, it can also be observed between nonmetals and metals.

-Atoms have similar electronegativities (the same affinity for electrons), covalent bonds are most likely to occur. Because both atoms have the same affinity for electrons and neither tends to donate them, they share electrons in order to achieve octet configuration and become more stable. In addition, the ionization energy of the atom is too large, and the electron affinity of the atom is too small for ionic bonding to occur.

Question 15

Predict whether bonding in a compound or between a pair of elements would be covalent or ionic.

Answer 15

One way to predict the type of bond that forms between two elements is to compare the electronegativities of the elements. In general, large differences in electronegativity result in ionic bonds, while smaller differences result in covalent bonds

Question 16

Be able to use the periodic table to predict the form of the stable ion for representative elements.

Answer 16

-The ions become stable when they acquire complete octet. The positive and negative value of ion denotes the number of electrons gained or lost. Therefore, the most stable ions for Na, Mg, Al, S, Cl, K, Ca, and Ga are Na+, Mg2+, Al3+, S2−, Cl−, K+, Ca2+ and Ga3+ respectively.

Question 17

explain what we mean when we use the term formula unit when referring to an ionic compound

Answer 17

-The reason for the term “formula unit” is that it is useful when we talk about how much of one substance is required to combine with a particular amount of another substance. For example: to make the smallest amount of hydrogen carbonate we combine one molecule of water with one molecule of carbon dioxide.

-But now suppose we want to combine silver nitrate with sodium chloride. Both are ionic compounds; they do not form molecules. In this case you would say that one formula unit (FU) of sodium chloride combines with one FU of silver nitrate.

-indicates the lowest reduced ratio of ions in the compound.

Question 18

Define the term crystal lattice energy and be able to compare lattice energy of binary ionic compounds.

Answer 18

-Crystal Lattice Energy: Lattice energy is defined as the energy released when the constituent atoms are placed in their respective positions on the crystal lattice. It can also be defined as the amount of energy that is spent to separate an ionic crystal into its constituent ions. It can be evaluated considering different contributions to the potential energy. In an ionic solid there are present three types of interactions

-Inversely proportional to the distance between the ions. The farther the distance between the ions in a lattice, the weaker the electrostatic forces holding them together, and the lower the lattice energy.

Question 19

State some differences in properties between ionic and covalent compounds.

Answer 19

Covalent compounds are held together by strong covalent bonds, while ionic compounds are held together by ionic bonds. Ionic compounds are typically soluble in water, while covalent compounds are not. Covalent compounds also tend to be more flammable than ionic compounds

• 1. Mass = It does not depends upon the covalent or the Ionic bond. It is the properties of the matter which can never be change.
• 2. Conductivity = Ionic compounds which are solids consist the ions but these ions are held together by the electrostatic force of the attraction so they do not become mobile in the solid state.
• But when the compounds are melted or dissolved in aqueous solutions, there force becomes weak and ions becomes mobile and hence they conducts the electricity.
• On the other hand, Covalent bond are non-conducing. Only Polar molecules of the Covalent bonds conducts the electricity.

Question 20

Explain how covalent bonding occurs.

Answer 20

occurs when pairs of electrons are shared by atoms. Atoms will covalently bond with other atoms in order to gain more stability, which is gained by forming a full electron shell. By sharing their outer most (valence) electrons, atoms can fill up their outer electron shell and gain stability.

Question 21

Describe what constitutes a region of high electron density (RHED) around a central atom

Answer 21

-Theory is a model used to predict 3-D molecular geometry based on the number of valence shell electron bond pairs among the atoms in a molecule or ion

Question 22

Define the term molecular geometry and explain how it is different from the electronic geometry.

Answer 22

-Electron-group geometry is determined by the number of electron groups.

-Molecular geometry, on the other hand, depends not only on the number of electron groups, but also on the number of lone pairs. When the electron groups are all bond pairs, they are named exactly like the electron-group geometry.

Question 23

Explain why one needs to draw a complete Lewis structure and determine its electronic geometry before correctly determining the molecular geometry.

Answer 23

it is the first step in predicting shapes of molecules. The Lewis structure helps us identify the bond pairs and the lone pairs. Then, with the Lewis structure, we apply the valence-shell electron-pair repulsion (VSPER) theory to determine the molecular geometry and the electron-group geometry

Question 24

Explain how lone pairs affect the predicted angles in a molecular geometry.

Answer 24

Lone pairs are in orbitals that are shorter and rounder than the orbitals that the bonding pairs occupy. Because of this, there is more repulsion between a lone pair and a bonding pair than there is between two bonding pairs.

Question 25

Determine whether a molecule is polar or non-polar.

Answer 25

-If the arrangement is symmetrical and the arrows are of equal length, the molecule is nonpolar. If the arrows are of different lengths, and if they do not balance each other, the molecule is polar. If the arrangement is asymmetrical, the molecule is polar.

Question 26

Cite the main idea of the valence bond (VB) theory.

Answer 26

-According to the valence bond theory, Electrons in a molecule occupy atomic orbitals rather than molecular orbitals. The overlapping of atomic orbitals results in the formation of a chemical bond and the electrons are localized in the bond region due to overlapping.

Question 27

Use the VB theory to describe how sigma and pi bonds form.

Answer 27

• Sigma bonds occur when the orbitals of two shared electrons overlap head-to-head. Pi bonds occur when two orbitals overlap when they are parallel.
• Sigma and pi bonds are types of covalent bonds that differ in the overlapping of atomic orbitals. Covalent bonds are formed by the overlapping of atomic orbitals. Sigma bonds are a result of the head-to-head overlapping of atomic orbitals whereas pi bonds are formed by the lateral overlap of two atomic orbitals