Chemistry S N O W F L A K E S Courtesy of SnowCrystals.com Kenneth G. Libbrecht, Caltech

Ever Happened to You?

UGLY!!!

Snow can be beautiful…

A Closer Look at Snow…

What Are Snowflakes? Snowflakes are NOT frozen raindrops. Sometimes raindrops do freeze as they fall, but this is sleet . Sleet particles don't have any of the elaborate and symmetrical patterning found in snow crystals. Snowflakes are crystals of H 2 O that form when conditions are right.

Snowflakes are NOT frozen raindrops.

Sometimes raindrops do freeze as they fall, but this is sleet . Sleet particles don't have any of the elaborate and symmetrical patterning found in snow crystals.

Formation of Snowflake Crystals???

Snowflakes form when water vapor condenses around a dust particle directly into ice, which happens in the clouds. The patterns emerge as the crystals grow. How Snowflakes Form

Water molecules in an ice crystal form a hexagonal lattice, as shown below: Red balls represent Oxygen Grey sticks represent Hydrogen Intermolecular forces between O’s & H’s link molecules

Water molecules in an ice crystal form a hexagonal lattice, as shown below:

Red balls represent Oxygen

Grey sticks represent Hydrogen

Intermolecular forces between O’s & H’s link molecules

How Big Do Snowflakes Get? The average snowflake measures around 1.2cm. You do need a magnifying glass to see the shape. Some of the largest snowflakes range from three to four inches in length!

So Many Shapes…How Can We Keep Them All Straight?

Systems for Classifying International Classification System Simple but widely used Seven main types Ukichiro Nakaya 41 distinct types Magono and Lee Most complex 80 types

International Classification System

Simple but widely used

Seven main types

Ukichiro Nakaya

41 distinct types

Magono and Lee

Most complex

80 types

Morphology Diagram

Simple Prisms Hexagonal Solid “faces” Glass-pane look

Hexagonal

Solid “faces”

Glass-pane look

Hollow Column Cone-shaped hollow regions at ends Hexagonal column Very small, relatively

Cone-shaped hollow regions at ends

Hexagonal column

Very small, relatively

Stellar Plates Form near -2 ° C or near -15 ° C Six broad arms Star-like shape

Form near -2 ° C or near -15 ° C

Six broad arms

Star-like shape

Stellar Dendrites Plate-like basic shape “ Tree-like” branches and sub-brances Fairly large Easily seen with naked eye

Plate-like basic shape

“ Tree-like” branches and sub-brances

Fairly large

Easily seen with naked eye

12-Sided Two stellar-dendrites grown together Rotated 30 ° Very rare

Two stellar-dendrites grown together

Rotated 30 °

Very rare

How Does Knowledge of Snowflakes Apply to Life? Ski slopes sometimes need to make their own snow The entire computer industry rests on silicon and other semiconductor crystals We don't know much about how these crystals form Maybe similar to snowflakes Knowledge is never useless!

Ski slopes sometimes need to make their own snow

The entire computer industry rests on silicon and other semiconductor crystals

We don't know much about how these crystals form

Maybe similar to snowflakes

Knowledge is never useless!

Growing Snow in a Lab??? Vapor diffusion chamber - an insulated box that is kept cold on the bottom (-40 ° C) and hot on the top (+40°C). A source of water is placed at the top, and water vapor diffuses down through the box, producing supersaturated air. The cold, supersaturated air at the center of the chamber is ideal for growing ice crystals.

Basil Mason’s Electric Wire Putting a wire into the diffusion chamber and then applying a high voltage to the wire, slender snow crystals begin growing from the wire. Since water molecules have an intrinsic electric polarizability, the electric fields tend to polarize the water molecules. The electric effects come about because electric fields influence the way water molecules diffuse through the air in the vicinity of the ice surface. wire crystal

Putting a wire into the diffusion chamber and then applying a high voltage to the wire, slender snow crystals begin growing from the wire.

Since water molecules have an intrinsic electric polarizability, the electric fields tend to polarize the water molecules.

The electric effects come about because electric fields influence the way water molecules diffuse through the air in the vicinity of the ice surface.

Better Snowflakes Through The best electric needle snowflakes grow only when certain chemical vapors are added to the diffusion chamber. Silicon caulk vapor Acetic acid vapor Gasoline vapor Chemistry

The best electric needle snowflakes grow only when certain chemical vapors are added to the diffusion chamber.

Silicon caulk vapor

Acetic acid vapor

Gasoline vapor

Artificial Snow Snow machines shoot a mixture of water and compressed air out of nozzles. The water comes out as fine droplets, and the air cools as it decompresses, causing the droplets to freeze. A fan blows the ice particles onto the slopes. You can see from the picture at left that artificial snow is made of frozen water droplets, with none of the elaborate structure found in real snow crystals.

Snow machines shoot a mixture of water and compressed air out of nozzles. The water comes out as fine droplets, and the air cools as it decompresses, causing the droplets to freeze. A fan blows the ice particles onto the slopes.

You can see from the picture at left that artificial snow is made of frozen water droplets, with none of the elaborate structure found in real snow crystals.

This has been a presentation of Gary G. Abud, Jr. http://getgabud.blogspot.com