ch. 1 - structure props

CHAPTER 1STRUCTURE & PROPERTIES OF MATERIALS

SHIP MATERIALS / LGB 21203

DEPARTMENT TECHNICAL FOUNDATIONS (TECHFO)- UNIVERSITI KUALA LUMPUR : MALAYSIAN INSTITUTE OF MARINE ENGINEERING TECHNOLOGY –

( UNIKL MIMET )


DEPARTMENT OF APPLIED SCIENCE & ADVANCED TECHNOLOGY (ASAT)- UNIVERSITI KUALA LUMPUR : MALAYSIAN INSTITUTE OF MARINE ENGINEERING TECHNOLOGY –

( UNIKL MIMET )

1. Introduction 1.1 Material science and Materials Engineering

2. Nature of metals, ceramic, polymers and composites.

3. Chemical, physical and mechanical properties.

4. Atomic structure and bonding 4.1 Atomic structure 4.2 Primary bonding (covalent, ionic, metallic). 4.3 Secondary bonding (Van Der Waals).

5. Crystal structures and crystal geometry. 5.1 7 crystal system and 14 Bravais lattice. 5.2 Common metal crystal structure(BCC, FCC and HCP). 5.3 Calculation of Atomic Packing Factor(APF) 5.4 Calculation of density.

6. Miller Indices: Position, Plane & Direction

CONTENT:



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INTRODUCTION:What’s the difference

between materials science and materials

engineering?

Materials engineering is mainly concerned with the

use of fundamental & applied knowledge of materials so that the

materials can be converted into products.

Materials science is primarily concerned with the search of basic knowledge

about the internal structure, properties & processing of

materials



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TYPE OF MATERIALS & THEIR PROPERTIES:

POLYMERIC MATERIALS

COMPOSITE

MATERIALS

METALLIC MATERIAL

S

ELECTRONIC

MATERIALS

CERAMIC MATERIALS

Figure 1 Main classes of engineering materials

generally are poor electrical and thermal conductors.

most have low to medium strengths.

most have low densities. most are relatively easy to

process into final shape some are transparent.

many are relatively strong and ductile at room temperature.

some have good strength at high temperature.

most have relatively high electrical and thermal conductivities.

able to detect, amplify and transmit electrical signals in a complex manner.

are light weight, compact and energy efficient.

generally have high hardness and are mechanically brittle.

some have useful high temperature strength.

most have poor electrical and thermal conductivities.

have a wide range of strength from low to very high;

- some have very high strength-to-weight ratios (e.g. carbon-fiber epoxy materials).

- some have medium strength and are able to be cast or formed into a variety of shapes (e.g. fiberglass-polyester materials).

- some have useable strengths at very low cost (e.g. wood and concrete).



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STRUCTURE AND PROPERTIES OF MATERIALS:

“Structure of Materials” usually relates to the arrangement of its internal components.

Property is a material trait in terms of the kind and magnitude of response to a specific imposed stimulus.

All important properties of solid materials may be grouped into six different categories: mechanical, electrical, thermal, magnetic, optical, and deteriorative.

Figure 2 a) Perovskite structure (Winfried Koller) b) Structure of inorganic materials (ICSD database)

(a)

(b)



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ATOMIC STUCTURE:

Atoms are composed of 2 regions:Nucleus: the center of the atom that contains the mass of the

atomElectron cloud: region that surrounds the nucleus that contains

most of the space in the atomNucleus of protons

and neutrons

Electron cloud-Electron paths

at different energy level

The nucleus contains 2 of the 3 subatomic particles:

Protons: positively charged subatomic particles

Neutrons: neutrally charged subatomic particles

The 3rd subatomic particle resides outside of the nucleus in the electron cloud Electron: the subatomic

particle with a negative charge and relatively no mass

Figure 3 Atomic structure


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All of the protons and the neutrons

The 1st ring can hold up to 2 e-

The 2nd ring can hold up to 8 e-

The 3rd ring can hold up to 18 e-

The 4th ring and any after can hold up to 32 e-

BOHR MODEL OF THE ATOM:

Figure 4 Bohr model



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Particle Charge Mass (g) Location

Electron(e-) -1 9.11 x 10-28 Electron

cloud

Proton (p+) +1 1.67 x 10-24 Nucleus

Neutron (no) 0 1.67 x 10-24 Nucleus

SUBATOMIC PARTICLE:

Table 1 Physical properties of subatomic particle in atom



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PERIODIC TABLE:

Figure 5 Periodic table of the elements



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He2

4

ATOMIC NUMBER & ATOMIC MASS:

the number of protons in an atom

the number of protons and neutrons in an atom

Atomic mass

Atomic number

number of electrons = number of protons



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EXAMPLE – HYDROGEN ATOM:

Hydrogen atom is the simplest atom and consists of one electron surrounding a nucleus of one proton.



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ELECTRONIC STRUCTURE OF ATOMS:

Electrons are arranged in Energy Levels or Shells around the nucleus of an atom.• first shell a maximum of 2 electrons

• second shell a maximum of 8 electrons

• third shell a maximum of 8 electrons

Figure 6 Maximum number of electrons for each shell



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There are two ways to represent the atomic structure of an element

or compound;

Electronic Configuration

Dot & Cross Diagrams

With Dot & Cross diagrams elements and compounds are represented by Dots or Crosses to show electrons, and circles to show the shells. Ex:

With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells.

Nitrogen N X X

X

XX

X N7

14X

Ex: Correct electron configuration of Nitrogen (Z = 7),: 1s2 2s2 2p3 (spdf notation)

There are three main methods used to write electron configurations: orbital diagrams, spdf notation, and noble gas notation.

(Orbital notation)



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“No two electrons in the same atom can have the same set of 4 quantum numbers.”

That is, each electron in an atom has a unique address of quantum numbers.

ELECTRONIC STRUCTURE OF ATOMS: PAULI EXCLUSION PRINCIPLE

QUANTUMNUMBERS

QUANTUMNUMBERS

Number that specifies the properties of the

electrons.

n ---> shell 1, 2, 3, 4, ...

l ---> subshell 0, 1, 2, ... n - 1

ml ---> orbital -l ... 0 ... +l

ms ---> electron spin +1/2 and -

1/2

n ---> shell 1, 2, 3, 4, ...

l ---> subshell 0, 1, 2, ... n - 1

ml ---> orbital -l ... 0 ... +l

ms ---> electron spin +1/2 and -

1/2



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Electron Filling Order

– spdf NOTATION



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MOLECULAR BONDS: PRIMARY & SECONDARY BONDING

Chemical bonding between atoms occurs since there is a net decease

in the potential energy of atoms in the bonded state. That is, atoms in

the bonded state are in more stable energy condition than when they

are unbonded.BONDING

SECONDARYPRIMARY

1. IONIC2. COVALENT3. METALLIC

1. VAN DER WAALS2. HYDROGEN



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PRIMARY BONDING: IONIC BONDING

Ionic bonds can form between highly electropositive (metallic)

elements and highly electronegative (nonmetallic) elements. In the

ionization process electrons are transferred from atoms of

electropositive elements to atoms of electronegative elements,

producing positively charged cations and negatively charged anions.

The ionic bonding forces are due to the electrostatic or coulombic

force attraction of positively charged ions.

An example of a solid which has a high degree of ionic bonding is

sodium chloride (NaCl).



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The positive sodium ion and the negative chloride ion are strongly attracted to each other.

This attraction, which holds the ions close together, is a type of chemical bond called an ionic bond.

The compound sodium chloride, or table salt, is formed.

A compound is a pure substance containing two or more elements that are chemically bonded.



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PRIMARY BONDING: COVALENT BONDING

In covalent bonding the atoms most commonly share their outer s

and p electrons with other atoms so that each atom attains the

noble-gas electron configuration. Some atoms are unlikely to lose or gain electrons because the

number of electrons in their outer levels makes this difficult.

The alternative is sharing electrons.

The chemical bond that forms

between nonmetal atoms

when they share electrons is

called a covalent bond.



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Shared electrons are attracted to the nuclei of both atoms.

They move back and forth between the outer energy levels of each atom in the covalent bond.

So, each atom has a stable outer energy level some of the time.

The neutral particle is formed when atoms share electrons is called a molecule.



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PRIMARY BONDING: METALLIC BONDING

Metallic bonds account for many physical characteristics of

metals, such as;

Strength, Malleability, Ductility, Conduction of Heat and Electricity

and Luster

The outer electrons of metals are not very strongly held by the

nucleus

So they stray easily and can move from one atom to the next

Think of a “sea of electrons”

Outer energy levels overlap like covalent bonds



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Figure beside is a schematic illustration of

metallic bonding. The free electrons shield the

positively charged ion cores from mutually

repulsive electrostatic forces, which they would

otherwise exert upon one another; consequently

the metallic bond is nondirectional in character.

These free electrons acts as a “glue” to hold the

ion cores together.

Some general behaviors of the various materials types (metals, ceramics,

polymers) may be explained by bonding type. For example, metals ar good

conductors of both electricity and heat, as a consequence of their free

electrons. By way of contrast, ionically and covalently bonded materials are

typically electrical and thermal insulators,, due to the absence of large numbers

of free electrons.



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SECONDARY BONDING: VAN DER WAALS

Secondary, Van Der Waals are weak in comparison to the primary or

chemical ones; bonding energy are typically o the order of only 10 kJ/mol.

Secondary bonding forces arise from atomic or molecular dipoles. In

essence, an electric dipole exists whenever there is some separation of

positive and negative portion of an atom or molecule.

Dipole interactions occur between induced dipoles, between induced

dipoles and polar molecules, and between polar molecules.



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Very weak secondary bonding forces can develop between the atoms of

noble gas elements which have complete outer-valence-electron shell (s2 for

helium and s2p6 for Ne, Ar, Kr, Xe, and Rn).

This bonding forces arises because the asymmetrical distribution of electron

charged distribution in these atoms creates electric dipoles. At any instant

there is a high probability that there will be more electron charge on one

side of an atom than on the other.

Thus, in a particular atom, the electron charge cloud will change with time,

creating a “fluctuating dipole”. Fluctuating dipoles of nearby atoms can

attract each other, creating weak interatomic nondirectional bonds.

The liquefaction and solidification of the noble gases at low temperatures

and high pressures are attributed to fluctuating dipole bonds.

*Note that as the atomic size of the noble gases increases, the melting and boiling

points also increase due to stronger bonding forces since the electrons have more

freedom to create stronger dipole moments.

FLUCTUATING INDUCED DIPOLE BONDS



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Permanent dipole moments exist in some molecules by virtue of an

asymmetrical arrangement of positively and negatively charged regions;

such molecules are termed polar molecules.

Figure beside is a schematic representation of a hydrogen chloride

molecule; a permanent dipole moment arises from net positive

and negative charges that are respectively associated with the hydrogen

and chlorine ends of the HCL molecule.

Polar molecules can also induce dipoles in adjacent nonpolar molecules,

and a bond will for as a result of attractive forces between two

molecules. The magnitude of this bond will be greater than for

fluctuating induced dipoles.

POLAR MOLECULE - INDUCED DIPOLE BONDS

HCl

+ -



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The strongest secondary bonding type, the hydrogen bond is a special case

of polar molecule bonding.

It occurs between molecules in which hydrogen is covalently bonded to

fluorine (as in HF), oxygen (as in H2O), and nitrogen (as in NH3).

For each H-F, H-O, or H-N bond, the single hydrogen electron is shared with

the other atom. Thus, the hydrogen end of the bond is essentially a

positively charged bare proton that is unscreened by any electrons.

This highly positively charged end of the molecule is capable

of a strong attractive force with the negative end of

adjacent molecule as demonstrated in HF.

In essence, this single proton forms a bridge between two negatively

charged atoms. The magnitude of the hydrogen bond is generally greater

than that of the other types of secondary bonds.

PERMANENT DIPOLE BONDS

HF

HF

Hydrogen bond



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CRYSTAL STRUCTURE & CRYSTAL GEOMETRY: Solid materials may be classified according to the regularity with

which atoms or ions are arranged with respect to one another.

A crystalline material is one in which the atoms are situated in a repeating or periodic array over large atomic distances.

Some of the properties of crystalline solids depend on the crystal structure of the material, the manner in which atoms, ions, or molecules are spatially arranged. A crystal structure is a unique arrangement of atoms in a crystal and composed of a unit cell, a set of atoms arranged in a particular way; which is periodically repeated in three dimensions on a lattice.



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2 types:1. Crystalline materials2. Noncrystalline (or amorphous) materials

Noncrystalline materials• atoms have no periodic or

repeating packing.• crystal has no long range order • occurs for: -complex structures -rapid cooling

"Amorphous" = Noncrystalline

Crystalline materials• atoms pack in periodic or

repeating), arrays, over large atomic distances (long range order)

• typical of: -metals, many ceramics, some polymers

There is an extremely large number of

different crystal structures all having long

range atomic order, depending how you

ARRANGE and PACK it.



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Assumptions used to describe crystal structure:

i. When describing crystalline structures, atoms (or ions) are thought of as being solid spheres having well defines diameters.

ii. This is termed the atomic hard sphere model in which spheres representing nearest-neighbour atoms touch one another.



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7 CRYSTAL STRUCTURE & 14 BRAVAIS LATTICE:



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There are three (3) principle crystal structure for metals:

a. Face Centered Cubic (FCC)b. Body Centered Cubic (BCC)c. Hexagonal Closed Packed (HCP)

(a) (b) (c)

PRINCIPAL METAL STRUCTURE:



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Packing factor = total volume of spheres in box / volume of box.

In crystalline materials: Atomic packing factor = total volume of atoms in unit cell /

volume of unit cell (as unit cell repeats in space).

APF = Volume of atoms in unit cell*

Volume of unit cell

*assume hard spheres

ATOMIC PACKING FACTOR (APF) CALCULATION:

Adapted from Fig. 3.19, Callister 6e.

Lattice constant

close-packed directions

aR=0.5a



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Cubic unit cell is 3D repeat unit

Rare (only Po has this structure)

Close-packed directions (directions

along

which atoms touch each other) are

cube edges.

Coordination # = 6 (# nearest neighbors)

SIMPLE CUBIC (SC) STRUCTURE:

APF = a3

4

3(0.5a)31

atomsunit cell

atomvolume

unit cellvolume

• APF for a simple cubic structure = 0.52



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Geometry of BCC structure Geometry of FCC structure



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• Close packed directions are cube diagonals.

--Note: All atoms are identical; the center atom is shaded differently only for ease of viewing.

• Coordination # = 8

BODY CENTERED CUBIC (BCC) STRUCTURE:



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Atom are arranged at the corners of the cube with another atom at the cube center.

Since atoms are assumed to touch along the cube diagonal in BCC, the lattice parameter is related to atomic radius through:

3

4Ra

• APF for a body-centered cubic structure = p3/8 = 0.68

Close-packed directions: length = 4R

= 3 a

Unit cell contains: 1 + 8 x 1/8 = 2 atoms/unit cell

APF = a3

4

3( 3a/4)32

atoms

unit cell atomvolume

unit cell

volumea

R



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• Close packed directions are face diagonals.

--Note: All atoms are identical; the face-centered atoms are shaded differently only for ease of viewing.


Gold

FACE CENTERED CUBIC (FCC) STRUCTURE:



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Atom are arranged at the corners and center of each cube face of the cell.

The lattice parameter, a, is related to the radius of the atom in the cell through :

APF = a3

4

3( 2a/4)34

atoms

unit cell atomvolume

unit cell

volume

Unit cell contains: 6 x 1/2 + 8 x 1/8 = 4 atoms/unit cell

APF for a body-centered cubic structure = p/(32) = 0.74

(best possible packing of identical spheres)

Close-packed directions: length = 4R

= 2 a

22Ra

a



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AB

C• ABCABC... Stacking Sequence

• FCC Unit Cell

• 2D Projection

Zinc

HEXAGONAL CLOSED PACKED (HCP) STRUCTURE:

A sites

B sites

C sitesB B

B

BB

B BC C

CA

A



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• ABAB... Stacking Sequence

• APF = 0.74, for ideal c/a ratio of 1.633

• 3D Projection • 2D Projection

A sites

B sites

A sites Bottom layer

Middle layer

Top layer

Geometry of HCP structure



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Crystal Structure

Coordination #

APF Close Packed direction

Simple Cubic (SC)

6 0.52 Cube edges

Body Centered Cubic (BCC)

8 0.68 Body diagonal

Face Centered Cubic (FCC)

12 0.74 Face diagonal

Hexagonal Close Pack

(HCP)

12 0.74 Hexagonal side

Table 2 Comparison of crystal structure



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Density = mass/volume

mass = number of atoms per unit cell * mass of each atom

mass of each atom = atomic weight/avogadro’s number

n AVcNA

# atoms/unit cell Atomic weight (g/mol)

Volume/unit cell

(cm3/unit cell)Avogadro's number

(6.023 x 1023 atoms/mol)

THEORETICAL DENSITY:



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Example: Copper

Data from Table inside front cover of Callister (see previous slide):

• crystal structure = FCC: 4 atoms/unit cell• atomic weight = 63.55 g/mol (1 amu = 1 g/mol)• atomic radius R = 0.128 nm (1 nm = 10 cm)

-7

Vc = a3 ; For FCC, a = 4R/ 2 ; Vc = 4.75 x 10-23cm3

Result: theoretical Cu = 8.89 g/cm3



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Why? Metals have... • close-packing (metallic bonding) • large atomic mass

Ceramics have... • less dense packing (covalent bonding) • often lighter elements

Polymers have... • poor packing (often amorphous) • lighter elements (C,H,O)

Composites have... • intermediate values

metals > ceramic > polymer

(g

/cm

3)

Graphite/ Ceramics/ Semicond

Metals/ Alloys

Composites/ fibersPolymers

1

2

20

30Based on data in Table B1, Callister *GFRE, CFRE, & AFRE are Glass,

Carbon, & Aramid Fiber-Reinforced Epoxy composites (values based on 60% volume fraction of aligned fibers

in an epoxy matrix). 10

3 4 5

0.3 0.4 0.5

Magnesium

Aluminum

Steels

Titanium

Cu,Ni

Tin, Zinc

Silver, Mo

Tantalum Gold, W Platinum

Graphite Silicon

Glass-soda Concrete

Si nitride Diamond Al oxide

Zirconia

HDPE, PS PP, LDPE

PC

PTFE

PET PVC Silicone

Wood

AFRE *

CFRE *

GFRE*

Glass fibers

Carbon fibers

Aramid fibers



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A Miller index is a series of coprime integers that are inversely proportional to the intercepts of the crystal face or crystallographic planes with the edges of the unit cell.

It describes the orientation of a plane in the 3-D lattice with respect to the axes.

The general form of the Miller index is (h, k, l) where h, k, and l are integers related to the unit cell along the a, b, c crystal axes.

MILLER INDICES:



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MILLER INDICES: POINT COORDINATES

Point position specified in terms of its coordinates as fractional multiples of the unit cell edge lengths



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Miller indices used to express lattice planes and directions

x, y, z are the axes (on arbitrarily positioned origin)

a, b, c are lattice parameters (length of unit cell along a side)

h, k, l are the Miller indices for planes and directions -

expressed as planes: (hkl) and directions: [hkl]

Conventions for naming

– There are NO COMMAS between numbers

– Negative values are expressed with a bar over the number

Example: -2 is expressed

GENERAL RULES FOR LATTICE DIRECTIONS, PLANE S & MILLER INDICES

2



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MILLER INDICES: DIRECTION

Rules for determining Miller Indices:

Draw vector, and find the coordinates of

the head, h1,k1,l1 and the tail h2,k2,l2.

Subtract coordinates of tail from

coordinates of head

Remove fractions by multiplying by

smallest possible factor

Enclose in square brackets



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Rules for determining Miller Indices:

1. Determine the intercepts of the

face along the crystallographic

axes, in terms of unit cell

dimensions.

2. Take the reciprocals

3. Clear fractions

4. Reduce to lowest terms

MILLER INDICES: PLANE



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1. If an element has an atomic number of 34 and a mass number of 78, what is the:

a) number of protonsb) number of neutronsc) number of electronsd) complete symbol

2. Write the electronic configuration for the following elements;

Ca O

Cl Si

Na20

40

11

23

8

17

16

35

14

28 B 115

EXERCISE 1:



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3. Find the Miller indices for the points in the cubic unit cell below:

Note: J is on the left face of the cube, H is on the right face, K is on the front face and I is on the back face

4. Describe the hydrogen bond and what type of elements is this bond restricted.

ch. 1 - structure props

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