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Six Types: 1) Dipole - Dipole, 2) Hydrogen-Bonding, 3) London Dispersion, 4) Metallic, - PowerPoint PPT Presentation


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Forces holding crystals together. Six Types: 1) Dipole - Dipole, 2) Hydrogen-Bonding, 3) London Dispersion, 4) Metallic, 5) ionic, 6) Covalent (network solids). Types of Crystalline Solids.

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Six Types: 1) Dipole - Dipole, 2) Hydrogen-Bonding, 3) London Dispersion, 4) Metallic,

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Forces holding crystals together

  • Six Types:

    1) Dipole - Dipole,

    2) Hydrogen-Bonding,

    3) London Dispersion,

    4) Metallic,

    5) ionic,

    6) Covalent (network solids)


Types of Crystalline Solids

Ionic Solid: contains ions at the points of the lattice that describe the structure of the solid (NaCl).

Molecular Solid: discrete covalently bondedmolecules at each of its lattice points (sucrose, ice).


Types of Crystalline Solids

Atomic Solid: Atoms at the points of the lattice that describe the structure of the solid (only one type of atom – diamond, graphite, copper).


Types of Crystalline Solids


Types of Crystalline Solids

Molecular Solid: discrete covalently bondedmolecules at each of its lattice points (sucrose, ice).


Intermolecular forces

  • Intermolecular forces (IMF) have to do with

    the attraction between molecules

    versus

    the attraction between atoms within a molecule.


Molecular Solids

  • WITHIN MOLECULES,

    STRONG COVALENT BONDS

    BETWEEN MOLECULES,

    RELATIVELY WEAK FORCES (Intermolecular Forces)


Intermolecular forces

  • Two Types:

    1) Dipole - Dipole Forces

    Hydrogen-Bonding

    2) London Dispersion (van der Waals) Forces,


+

–

H

Cl

+

–

+

–

+

–

+

–

Dipole - Dipole attractions

  • Polar molecules have a separation of charge

  • Molecules are attracted to each other in a compound by these + and – forces.


Hydrogen - bonding

  • H-bonding is a special type of dipole - dipole attraction that is very strong

  • It occurs when N, O, or F are bonded to H

  • They are given a special name (H-bonding) because compounds containing these bonds are important in biological systems


Water Molecules


London Dispersion forces

  • Non-polar molecules do not have

    permanent dipoles.

  • London dispersion (or van der Waal) forces exist in non-polar molecules

    are due to small dipoles that are temporary.


London Dispersion forces

  • Because electrons are moving around in atoms,

    there will be instants when the charge around an atom is not symmetrical

  • The resulting tiny dipoles cause attractions between atoms/molecules


London Dispersion forces

  • relatively weakforces that exist among noble gas atoms and nonpolar molecules. (Ar, C8H18)


London forces

Induced dipole:

Instantaneous dipole:

Eventually electrons are situated so that tiny dipoles form

A dipole forms in one atom or molecule, inducing a dipole in the other


METALLIC SOLIDS

Atomic Solid: Metal Atoms at the points of the lattice.


Metallic BondingThe Electron Sea Model Regular Array of Cations in a “Sea” of Valence Electrons


B. Types of Bonds

Metals are good conductors because the valence electrons are able to flow freely

Valence electrons of metals can be thought of as a “sea of electrons”


B. Types of Bonds

Metallic Bonding - “Electron Sea”


B. Types of Bonds

  • Metallic Bonding

  • Metals are found in:

    • Groups 1 & 2

    • middle of table in 3-12

    • Below and to left of stairstep line

  • Have luster, are dutile and malleable


B. Types of Bonds

METALLIC

e- are delocalized among metal atoms, “electron sea”

Bond Formation

atom

Smallest Unit

Types of Elements

metals


IONIC SOLIDS

Contains ions at the points of the lattice (NaCl).

  • HIGH MELTING SUBSTANCES

  • HELD TOGETHER BY STRONG ELECTROSTATIC FORCES THAT EXIST BETWEEN OPPOSITELY CHARGES IONS


NaCl


II. Octet Rule

  • In the formation of compounds, atoms tend to achieve the electron configuration of a noble gas.

  • Atoms either gain, lose, or share electrons to form compounds.


III. Cations

Loses an e-

-An atom’s loss of valence electrons produces a cation, or a positively charged ion.


III. Cations

  • Metals – lose valence e- easily

  • Transition metals – have 2 valence e-, usually lose those two to form 2+ ions, but can also lose d electrons to form other ions


IV. Anions

  • Nonmetals easily gain e- to form negative ions to get to 8 valence e-

Gains an e-

Chloride ion


IV. Anions

  • -Nonmetals usually gain e-

  • Some can gain or lose, but will gain most often


Formula Unit

-The lowest whole-number ratio of ions in an ionic compound.


V. Ionic Bonds

  • When oppositely charged ions attract, electrostatic force that holds them together = ionic bond

  • Compounds containing ionic bonds = ionic compounds

  • Electrons are transferred from cations to anions

  • Bonds formed between metals and nonmetals (or contain a polyatomic ion)


V. Ionic Bonds

Na·

1s2 2s2 2p63s1 1s2 2s2 2p6 3s23p5

RESULTS IN

Na+

1s2 2s2 2p6 1s2 2s2 2p6 3s23p6


VI. Properties of Ionic Compounds

  • Most ionic compounds are crystalline solids at room temperature.

    • Arranged in repeating three-dimensional patterns

  • Ionic compounds generally have high melting points

    • Large attractive forces result in very stable structures


VI. Properties of Ionic Compounds

  • Ionic compounds can conduct an electric current when melted or dissolved in water.

    • When ionic compounds are dissolved in water the crystalline structure breaks down. This allows the ions to move freely which results in conductivity.


  • The positive Na ions move to the cathode and the negative Cl ions move to the anode.


NETWORK ATOMIC SOLIDS: (CARBON & SILICON)

SOLIDS CONTAINING STRONG DIRECTIONAL COVALENT BONDS TO FORM A SOLID THAT MIGHT BE BEST VIEWED AS A “GIANT MOLECULE”

EXAMPLE:

DIAMOND AND GRAPHITE


The Structures of Diamond and Graphite


The Structure of QuartzSi at the center of tetrahedralarrangement with 4 oxygen atoms.


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