Earth’s Materials - Atoms, Elements, and Compounds

Structure of an Atom

Uniqueness of Elements An elements is defined by its Atomic Number (number of protons in the nucleus) i.e. Hydrogen’s Atomic Number is 1 Helium’s Atomic Number is 2 Mass Number (sum of protons and neutrons) i.e. Hydrogen’s Mass Number is 1 Helium’s Mass Number is 4

Periodic Table

Isotopes - elements with different numbers of neutrons in the nucleus. e N P N e Helium 3 ( 3 He) P e e P N P Helium 4 ( 4 He)

Ions - atoms with excess positive or negative charge (gain or loss of electrons from the outermost shell). Cations (positive charge, lose electrons) P e Hydrogen atom P e ElectronHydrogen ion ( H + ) + + Anions (negative charge, gain electrons)

Compounds - combination of atoms of one or more elements in a specific ratio. Examples: N 2 - nitrogen gas H 2 O - water CaCO 3 – calcite (a mineral) Ions dissolved in water will combine to form compounds

Types of Bonds Ionic - transfer of electrons between cations and anions. Moderate strength, Moderate hardness

Covalent - electrons are shared between atoms Types of Bonds Strong bond/ Hard mineral

Minerals

Questions -Which of the following are minerals? Explain! A.Ice (H 2 O) B.Water (H 2 O) C.Oil (C x H y O z ) D.Salt (NaCl) E.Synthetic (man-made) Diamond (C) It may be helpful to write out the definition of a mineral.

Five Requirements to Be a Mineral Naturally formed Solid Formed by inorganic processes Specific chemical composition Characteristic crystal structure

Properties of Minerals Crystal Form and Habit Cleavage Hardness Luster, Color, Streak Density Taste Feel Magnetism Reaction to Acid

Most Common Elements Oxygen Silicon Aluminum Iron Calcium Magnesium Sodium Potassium Percentage by Weight

Common Mineral Families OxidesO 2 Carbonates(CO 3 ) 2- Sulfates(SO 4 ) 2- SulfidesS Phosphates(PO 4 ) 3 Halides(NaCl-salt) Native Elements (Gold) Silicates(SiO 4 ) 4- Which mineral family would be the most common at the Earth’s surface?

Silicon-Oxygen Tetrahedron (SiO 4 ) -4 – anion Building Block of Silicates Combination of ionic and covalent bonds Combines with other tetrahedrons and/or cations

Mineral Formation Combination of Tetrahedron and cations form minerals i.e. Olivine

Silicate Structures Si:O 1:3 Si:O 1:2.75 Si:O 1:2.5

Silicon content increases with complexity of Structure 1:4 1:3 1:2.75 1:2.5 1:2 Silicon:Oxygen

Structure and Cleavage

Chemical Classification Ferromagnesium (Mafic) Silicates –Composed of Iron (Fe) and Magnesium (Mg) –Dark in Color Nonferromagnesium (Felsic) Silicates –Composed of Potassium (K), Sodium (Na), Calcium (Ca), etc. no Fe and Mg –Lower density –Light in Color Hornblende Orthoclase