Three-Dimensional Structure

Question 1

Ionic Crystals

What is an ionic crystal?

Answer 1

• Due to the attractive forces that exist between the positive and the negative charges in an ionic compound, the ions will actually pack together very tightly, forming a 3D figure known as a “crystal lattice”. The lattice is a pattern of alternating positive and negative ions. Each ion is attracted to all the adjacent ions to it, of the opposite charge. So, when sodium ions and chloride ions join together to form NaCl, the formula NaCl(s) actually is referring to the ratio of sodium to chloride ions in the crystal(so in this crystal, they would be in 1:1 ratios). In CaF2, we would have a ratio of one calcium ion to two fluoride ions. The smallest ratio of ions in a crystal is called a formula unit.
• Some crystals are cubed, some are needle-like, and some are hexagonal columns. The shape depends on the way the ions pack together. The sizes and charges of the ions will also affect the pattern of the packing. If the crystals form slowly, the packing of the ions is uniform.

Question 2

Network Solids

What are network solids?

Answer 2

• In a network solid (covalent bonding)- millions of atoms of the same element or two different elements, are covalently bonded in a variety of patterns. Four examples of network solids are carbon, but they have different physical properties, so we call them allotropes.
• Some network solids consist of two different elements- the most common compound in Earth’s crust, silicon dioxide, is one example. Sand and quartz consist almost entirely of silicon forming double bonds with the oxygen atoms. But, this is not typical for silicon. Instead silicon bonds to four oxygen atoms to form a tetrahedral shape.

Question 3

Exceptions to the Octet Rule
The rule you have been provided with in terms of lewis structures, apply to almost all molecules. However, some exceptions to these rules are inevitable.

Answer 3

Elements that we can count on to obey the octet rule are carbon, nitrogen, oxygen and fluorine. On the flip side, some atoms exceed the octet rule. This behaviour is observed only for those elements in period three of the periodic table, and beyond. Some atoms can be electron deficient, and some can have a hyper octet,(exceeding eight electrons).

Question 4

Provide 3 examples of ionic crystals found at home or in nature.

Answer 4

1. Crystal of sodium chloride- common table salt.
2. Crystal of sucrose- common table sugar.
3. Crystalline form of pure carbon- uncut diamond.

Question 5

According to laboratory evidence, each ion is attracted to all…

Answer 5

adjacent ions of the opposite charge.

Question 6

What is a unit cell?

Answer 6

The smallest set of ions in a crystal that’s repeated over and over.

Question 7

The smallest ratio of ions in a crystal such as NaCl(s) is called a…

Answer 7

formula unit.

Question 8

What are the two factors that affect the shape of an ionic crystal?

Answer 8

a) The size of each ion.

b) The relative charge of each ion.

Question 9

Why do ionic compounds exist in crystals while molecular compounds exist in molecules?

Answer 9

Ionic compounds are attracted to the opposite changed ion adjacent to them, whereas covalent bonds exist between pairs of atoms.

Question 10

In ionic compounds with polyatomic ions, the two types of bonds present are_____(within the polyatomic ion) and ________(between the metal and polyatomic ion). Why do these compounds often decompose before they melt?

Answer 10

-Intramolecular
-Intermolecular
The intramolecular bonds are stronger than the intermolecular, causing them to decompose.

Question 11

Explain each of these ionic compound properties:

• Solid at SATP
• Hard, brittle, break along smooth planes

Answer 11

• The crystal structure of the ionic bonds creates solids with high melting points and boiling points.
• The ions are close together and electrostatic repulsion(external forces) causes them to shatter.
• Ionic compounds have stronger bonds and all of the bonds must be broken to melt or boil.

Question 12

Explain each of the metallic crystal properties:

• Shiney, silvery
• Flexible
• Conductive
• Crystalline

Answer 12

• The free electrons come into contact when they move which increases their energy. When the energy is released the metal shines.
• The delocalized electrons move around with external forces which allows the atoms to shift, making them malleable and ductile.
• The electrons hold energy and flow through the metal to the output and release the energy.
• The bonds form in tightly packed forms.

Question 13

Solids that result from______ bonding, where the valence electrons are not held strongly by their atoms so they are free to move(electron sea).

Answer 13

-Metallic crystal

Question 14

Properties of molecular crystals
Pick the correct one and explain it.
a) hard, not very hard, soft
b) relatively low m.p. or relatively low m.p.
c) conductive or non-conductive

Answer 14

Soft-intermolecular bonds are very weak.
relatively low m.p.-bonds can be easily broken.
non-conductive-valence electrons are not delocalized.

Question 15

What are the properties of covalent network solids?

Answer 15

• Hard brittle solids
• High melting points
• Don’t dissolve in water or conduct

Question 16

In what two ways are covalent networks similar to ionic compounds?

Answer 16

a) Both are hard and brittle

b) both have high melting points

Question 17

Stereochemistry

Stereochemistry is the study of the…

Answer 17

relative spatial arrangement of atoms that form the structure of molecules and their manipulation.

Question 18

Stereochemistry

Valence-Shell Electron Pair Repulsion Theory(VSEPR) is used to…

Answer 18

predict the three-dimensional shape of a molecule.

Question 19

Stereochemistry

VSEPR is based on the electrostatic repulsion of electron pairs…

Answer 19

that causes them to take positions as far apart in a molecule as possible.

Question 20

Stereochemistry

A lone pair(LP) of electrons spreads out more than…

Answer 20

a bonding pair does, therefore, the repulsion is greatest between two lone pairs.

Question 21

Stereochemistry
Bonding pairs(BP) are more localized between the atomic nuclei and, therefore, spread out less than...

Answer 21

the lone pairs, as a result, the repulsion between two bonding pairs is less than that between two lone pairs.

Question 22

Stereochemistry

The repulsion between and lone pair and a bonding pair is…

Answer 22

moderate.

Question 23

Stereochemistry

The order of repulsion can be expressed as:

Answer 23

LP-LP>LP-BP>BP-BP

Question 24

Stereochemistry
In the following molecules:
A represents
X represents
E represents
m is the
n is the

Answer 24

• the central atom
• any atom bonded to the central atom
• a lone pair
• subscript that indicates the number of bonded atoms
• subscript that indicates the number of lone pairs on the bonded atom.

Question 25

Shapes of Molecules Linear molecule -Have a central atom with... -The angle between the two bonds-the bond angle- is___. The symbol in___, means there are two atoms bonded to the central atom and no lone pairs.

Answer 25

-2 electrons groups that make a linear shape because the electron groups exert repulsive forces on each other that move them as far away as possible. -180° -Ax2 Image:https://www.google.com/urlsa=i&url=https%3A%2F%2Fen.wikipedia.org%2Fwiki%2FVibrational_spectroscopy_of_linear_molecules&psig=AOvVaw0HNYde_gr3RoO01oBe9X6l&ust=1637645485157000&source=images&cd=vfe&ved=0CAsQjRxqFwoTCMCo7_2eq_QCFQAAAAAdAAAAABAD

Question 26

``` Shapes of Molecules Trigonal Planer molecule -Have a central atom with... -The bond angle is___. -The general symbol is___, which means there are three atoms bonded to the central atom. -Trigonal planar shapes have... ```

Answer 26

- 3 electron groups to make a Trigonal planer shape. - 120° - Ax3 - one central atom with three electron groups that lie in a flat plane. All of the electron groups may consist of bonding electrons or one of the electron groups may be a lone pair(AX2E), this makes a bent molecule.

Question 27

``` Shapes of Molecules Tetrahedral molecule -Have a central atom with... -The bond angles are___. -The symbol is___. -Tetrahedral shapes are... ```

Answer 27

- 4 electron groups to make a tetrahedral shape. - 109.5° - AX4 -4 bonding groups - Three-dimensional. You need to analyze the perspective until you can see that, lines going upward are in the plane of the page. The lower line on the right is coming out from the page and the upper line on the right is going into the page.

Question 28

Shapes of Molecules Trigonal Pyramidal molecule -Trigonal Pyramidal molecules are formed when a tetrahedral molecule has... -The lone pair exerts a... -The bond angles are about___. -The symbol is___. -These look like a tetrahedral missing...

Answer 28

- 3 bonding groups and one lone pair. - repulsive force on the three bonding groups; pushing them away causing the central atom to be the peak of the pyramid and the tree atoms to be the triangular base of the pyramid. - 107.3° - AX3E - the top bonding pair

Question 29

``` Shapes of Molecules Bent(V-Shaped) molecule -Bent molecules have... -There is repulsion between the two lone pairs due to their... -The bond angle is___. -The symbol is___. ```

Answer 29

- 2 lone pairs - bulkiness - 104.5° - AX2E