Earth Materials: MineralsEarth Materials: Minerals

Chapter 5. Patterns in Nature: Minerals1. Minerals: Why care?2. Atoms, ions & isotopes of the elements3. Atomic bonding and the formation of chemical compounds 4. Minerals: the building blocks of rocksInternal structure in relationship to physical properties 5. Introduction to rocks.

Today’s Lecture:

Minerals: Why care?

Examples:

Aluminum: Soft drink cans

Graphite (Carbon): Pencil lead and lubricant

Copper: Electrical components and wire

Talc: Baby powder

Silver, gold, gemstones: Jewelry

Silicon: Computer chips

Raw materials for nearly all of the manufactured products we use are obtained from minerals.

Malachite: Ore of copper and a gemstone.

Quartz: Source of silicon used in making computer chips

Galena: Ore of lead

Gemstones!

Other reasons:

Minerals: Why Care?

Rocks inform us about geologic hazards, such as volcanic eruptions, earthquakes etc., enabling us to make better decisions about how we interact with the Earth and use its resources (e.g. siting and designing buildings).

Rocks hold important clues for understanding processes of weathering and erosion. This information can help us use the Earth’s resources more effectively (e.g. extraction of mineral and petroleum resources, soil conservation, degradation of concrete structures, etc.).

Rocks enable us to understand our past & place our lives in proper evolutionary context.

To understand minerals we need to understand matter and how it is organized.

The three states of matter: Solid

Liquid

Gas

Understanding Matter…

Solids-Atoms and molecules organized into fixed structures with a defined shape (crystals, glass, plastics). Atoms move (vibrate) even in a solid! Just limited in a solid.

Liquids-Fluid mixtures of atoms and molecules existing as charged atoms or molecules (e.g. “ions”). Atoms in solutions can form loose associations with each through transient electronic “bonds”. However, the liquid lacks a fixed structure, like that seen in most solids.

Gases-Fluids in which atoms and molecules are in rapid motion, freely moving about with no fixed structure. Gases expand to fill the available space.

States of Matter

•Elements: Different types of atoms that, in their pure form, cannot be divided into other smaller units without changing their properties.

•Atom: Smallest division of an element, that still possesses the chemical properties unique to the element.

•Compounds: Two or more atoms bonded together. May be composed of atoms of the same element, or combinations of several different elements.

Bulding blocks of mineralsAtoms, elements and compounds: Building blocks of minerals

(See Science Toolbox 5.1, page 112 of text)

What is an atom?

An atom is made up of:

-A nucleus: Central region of atom where most of the mass resides. Comprised of protons and neutrons.

-Orbiting electrons: High-speed nearly “massless” particles of negative charge which orbit the nucleus.

electrons

nucleus

Understanding Matter…

Nucleus contains:

Protons = Particles with a mass of 1.0 and a positive electrical charge.

Neutrons = “ “ a mass of 1.0 and a neutral electrical charge. Neutrons may

be thought of as a proton bound to an electron.

electronsOrbiting the nucleus are eelectronslectrons having essentially no mass ands a negative charge.

A singleatom

neutrons

protons

Understanding Matter…

A simple “ Bohr” model for a single atom:

T&L: Figure 2.4 A

Understanding Matter…

...in reality

Nucleus of Nucleus of protonsprotonsand and neutronsneutrons

T&L: Figure 2.4 B

Structure of an Atom

Number of protons in the nucleus of an element is calledIts atomic number.

Elements are distinguished from each other by their atomic number.

nucleusnucleus

Model ofModel ofone atomone atom

Examples: All Helium atoms have 2 protons “ Carbon “ “ 6 “ “ Uranium “ “ 92 “

Types of Atoms and Elements

Mass Variations in Elements:

The number of protons plus the number of neutrons in the nucleus defines the atomic mass of the element.

However, most elements come in different “species”- versions that differ slightly in mass because of having different numbers of neutrons in the nucleus.

These “species”of elements are called isotopes.

Isotopes: Same element, different massIsotopes: Same element, different mass

Example: Carbon-14

Again… mass variations of the same element are called “isotopes”.

Many isotopes are unstable, and disintegrate through a process called radioactive decay where particles and/or energy are emitted from the nucleus

C14

is unstable

The rate of radioactive disintegration is constant, so they can be used as a kind of clock for dating rocks!

Isotopes: Atoms that vary in the number of neutrons in the nucleus

Number of protons determines the type of atom

6 protons = carbon

Number of neutrons in an atom can vary. Number of neutrons plus the number of protons equals the

atomic “mass”. Here are the three isotopes of Carbon: 6 protons & 6 neutrons: mass number = 12 6 protons & 7 neutrons: mass number = 13 6 protons & 8 neutrons: mass number = 14

13C

12C

14C

How we write it

Let’s review using Carbon as an example:

Classifying the Elements

equals # of protons

6 => 6 protons

Periodic table of the elements

Elements are classified by the number of protons in the nucleus (I.e., their atomic number)

112 known elements

Only 92 occur naturally

Classifying the Elelemnts

Hydrogen

Calcium

Oxygen

Aluminum

Gold

Helium

Iron

Titanium

You’ve heard of many of these elements, for example:

Classifying the Elements

When atoms give away or gain electrons, theyare no longer electrically neutral. In other words,They take on an electrical charge.

Any atom possessing a charge is called an “ion”.

Atoms with a positive charge are called “cations”.Those with a negative charge are called “anions”.

Ions: Charged Atoms

Atoms that lose or gain electrons develop a charge.

Different elements combine to make chemical compounds…

Example 1: water (2 hydrogen atoms + 1 oxygen atom = H2O)

Example 2: salt (1 sodium atom + 1 chlorine atom = NaCl)

~ 4000 minerals on Earth!Making Minerals

Minerals are naturally-occurring compounds that are classified by their:

Chemical composition

Internal (“atomic”) structure

QuartzQuartz contains: contains:

siliconsilicon (Si) and (Si) and oxygenoxygen (O) (O)

elementname symbol

Example: Quartz

Chemical formula for quartz is: SiO2

-> To be considered a mineral, it must:

1. Occur naturally

What are minerals?

2. Be inorganic

3. Be a solid

5. Have a defined chemical composition

4. Possess an orderly internal structure

Definition of a mineral:

Atomic Bonding

How do different elements combine to form compounds?

=> By bonding between atoms!

3 main ways:

“Ionic bonding” - loaning electrons

“Covalent bonding” - sharing electrons

“Metallic bonding” - electrons are free to move about from atom to atom

Making Compounds

Ionic Bonding

Example: Table Salt: Sodium (Na) and Chlorine (Cl)

Sodium gives up an electron becoming a positively-charged charged cation.

Chlorine picks up the electronfrom Sodium taking becoming a negatively charged anion.

Atomic Bonding

The atoms bond based on these charge differences.

Example: Sodium (Na) and Chlorine (Cl)

Atoms arrange in orderly fashion: w/ alternating sodium and chlorineatoms, so each negative ion is surrounded by positive ions, and visa versa.

Ionic Bonding

Example: Sodium (Na) and Chlorine (Cl)

Such orderly arrangement at the atomic level produces specific shapesin crystals at the macroscopic level that reflect the atomic structure

Crystal Form Reflects Internal StructureCrystal Form Reflects Internal Structure

The structure of minerals depends on:

Size of the ions involved

Electrical charge of the ions involved

Crystal Form Reflects the Internal Arrangement of Atoms