Unit 3 Chp 12 notes B and L.ppt

Unit 3

Chapter 12

Solids

• Two major types.

• Amorphous

- those with much

disorder in their structure.

(Ex. Rubber, glass, obsidian)

• Crystalline

- have a regular

arrangement of components

in their structure. (Ex.

Types of Solids

Types of Solids

 Amorphous solids:_{Amorphous solids:}

considerable disorder in

considerable disorder in

their structures (glass).

their structures (glass).

 Crystalline Solids:_{Crystalline Solids:} highly highly regular arrangement of

Representation of Components in a

Representation of Components in a

Crystalline Solid

Crystalline Solid

Crystal Lattice

Crystal Lattice: A 3-: A 3-dimensional system of

dimensional system of

points designating the

points designating the

centers of components

centers of components

(atoms, ions, or molecules)

(atoms, ions, or molecules)

that make up the

that make up the

substance.

Three Main Types of crystalline solids

Three Main Types of crystalline solids

based on the individual units in the solid and their

attachment to each other:

1. Molecular solids 2. Ionic solids

3. Atomic solids (three sub categories)

1.Nonbonding 2.Metallic

3.Network Covalent

1. Molecular solids

Have molecules held together by intermolecular forces

(can be any of the three: LDF, Dipole or H-bonding)

Properties:

•2 or more nonmetals •Soft

2. Ionic Solids

Composed of ions held by Coulombic attractions between the cations and anions in the lattice. Regular/ordered arrangement of ions.

Properties:

•Between metal and nonmetal •high melting points

•brittle

•conductors in aq form or liquid

•Poor conductor of heat and electricity in solid state

3. Atomic Solids

Can be broken into three sub-categories: 1.Nonbonding atomic solids

2.Metallic atomic solids 3.Network covalent

solids

A. Nonbonding atomic solids

Include the noble

gases, such as neon and helium. Held

together by weak LDFs only

Properties:

B. Metallic atomic solids

Have metallic bonds involving metal cations with delocalized sea of electrons. Could be

alloy.

Properties:

•Between only metals

•Good conductors as s or liquids

REMINDER: Properties of metal

alloys:

1. Understood in terms of size of component atoms:

A. Interstitial alloys

B. Substitutional alloys

2. Typically remain a sea of mobile e- and remain

conducting.

C. Network covalent solids

Have many and very strong covalent bonds, regular and irregular arrangements

Properties:

•Nonmetals (or metalloids) only

•3-D network rigid and hard

•_{high melting points} (Bonds must break)

15

Ex: diamond,

Diamond

tetrahedrally to four other carbon atoms with

covalent bonds.

*Electrons are held in position and not free to flow, they do not conduct electricity.

Graphite

trigonal planar

arrangement.

*Held together in planes by delocalized pi bonds.

Therefore graphite will conduct electricity.

*Weak LDF between sheets allow sheets to move past each other explaining why it is soft

Semiconductors

*Covalent Network Crystals can have properties as semiconductors.

*Only C, Si, Ge and Sn b/c they can form 4 covalent bonds in an infinite network.

Si used most frequently due to its unique properties:

1. Forms 3-D network similar to diamond 2. Conductivity increase w/ temp

Process of Doping

Doping: Process of adding controlled amts of impure atoms to a material to assist w/ conductivity:

*n-type: adding an atom w/ one more e- than Si (n = negative charge carrying)

*p-type: adding an atom w/ one less e- than Si (p = positive charge carrying)

Review Questions:

1. Which of the following elements, if doped

with Silicon, would yield an n-type

semiconductor: Ga, As or C?

As – it has 5 valence

e-2. Suggest an element that could be used to

dope silicon to yield a p-type material.

AP Sample Question

The best explanation for the fact that diamond is

extremely hard is that diamond crystals

A.are made up of atoms that are intrinsically hard because of their electronic structures

B.consist of positive and negative ions that are strongly attracted to each other

C.are giant molecules in which each atom forms strong covalent bonds with all of its neighboring atoms

D.are formed under extreme conditions of temperature and pressure

AP Sample Question

Which of the following could be the identity of

a white crystalline solid that exhibits the

following properties?

•It melts at 320°C.

•It does not conduct electricity as a solid.

•It conducts electricity in an aqueous solution.

A.C

H

O

(

s

)

B.NaOH(

s

)

C.SiO

(

s

)

AP Sample Question

Which of the following substances is a

strong electrolyte when dissolved in water?

A.Sucrose

B.Ethanol

C. Sodium nitrate

D. Acetic acid

AP Sample Question

A certain crystalline substance that has a

low melting point does not conduct electricity

in solution or when melted. This substance

is likely to be

A.a covalent network solid

B.a metallic solid

C.a polymer

D.an ionic solid

E.a molecular solid

AP Sample Question

A sample of a hard, solid binary compound at

room temperature did not conduct electricity as a

pure solid but became highly conductive when

dissolved in water. Which of the following types of

interactions is most likely found between the

particles in the substance?

A.Ionic bonds

AP Sample Question

At room temperature I

(

s

) is a molecular solid.

Which of the following provides a characteristic of

I

(

s

) with a correct explanation?

A.It has a high melting point because it has weak

intermolecular forces.

B.It is hard because it forms a three-dimensional

covalent network.

C.It is not a good conductor of electricity because its

valence electrons are localized in bonding and

nonbonding pairs.

D.It is very soluble in water because its molecules

The structure of one form of boron nitride is

represented above. This form of boron nitride is one of the hardest substances known. Which of the following best helps explain why boron nitride is so hard?

A.Boron ions and nitrogen ions are held together by ionic bonds.

B.Boron nitride is a network solid of atoms connected by covalent bonds with fixed bond angles.

C.Boron nitride is an alloy, and alloys are typically harder than the elements used to make them.

AP Sample Question

Solid ethyl alcohol, C

H

OH is best categorized

as:

(A) A network solid with covalent bonding

(B) A molecular solid with zero dipole moment

(C) A molecular solid with hydrogen bonding

(D) An ionic solid

(E) A metallic solid

Based on the diagram above, which of the following best helps to explain why MgO(s) is not able to conduct

electricity, but MgO(l) is a good conductor of electricity? A.MgO(s) does not contain free electrons, but MgO(l) contains free electrons that can flow.

B.MgO(s) contains no water, but MgO(l) contains water that can conduct electricity.

C.MgO(s) consists of separate Mg2+ ions and O2− ions, but MgO(l)

contains MgO molecules that can conduct electricity.

D.MgO(s) consists of separate Mg2+ ions and O2− ions held in a

Types of Crystals Summary: