Earth Chemistry & Minerals Chapter 2 Earth Chemistry & Minerals

Section 1 Matter Matter is anything that takes up space and has mass. Physical properties are those characteristics that can be observed without changing the chemical composition of the substance. Examples include color, density, hardness, etc. Chemical properties are those characteristics that describe how a substance interacts with other substances to produce different kinds of matter. An example includes iron reacting with oxygen to form rust.

Section 1 Elements Matter is made up of elements. An element is a substance that has a characteristic set of physical and chemical properties. Silicon and oxygen are the two most abundant elements in the Earth’s crust. Together they make up almost 75% of the crust. Over 90 elements occur naturally in the Earth. Only 8 make up over 98% of the crust. Elements consist of atoms.

Atoms An atom is the smallest unit of an element that cannot be broken down by chemical means. They are made up of smaller subatomic particles: electrons, protons, and neutrons

The Atom Electrons carry a negative electric charge, protons carry a positive charge, and neutrons are neutral. The protons and neutrons make up the nucleus of an atom. The electrons move around the nucleus in the electron cloud in different “energy levels” or “valence shells”. The first level can hold up to 2 electrons. While the second and third can hold up to 8 each.

The Atom The atomic number is equal to the number of protons in an atom. The mass number is the sum of the protons and neutrons in an atom measured in amu. Isotopes are atoms of the same element that differ in mass number by having a different number of neutrons.

States of Matter There are three main states of matter. They are solids, liquids, and gases. A solid has a definite shape and volume. The particles that make up a solid are packed tightly together in fixed positions. A liquid has a definite volume but not shape. It takes the shape of its container. The particles are tightly packed, but they are free to move around each other. A gas has no definite shape or volume. The particles are farther apart and move freely. It expands in all directions.

Section 2 Combinations of Atoms A compound is when the atoms of two or more elements are chemically united. It has properties different than the elements that compose it. The smallest complete unit of a compound is a molecule. Diatomic molecules are made up of two atoms, such as O2.

Chemical bonding Chemical bonds are the forces that hold atoms together in a compound. Ionic bonds are when electrons are transferred from one atom to another. An ion is an atom or group of atoms that carries an electrical charge, opposites attract. Covalent bonds form when atoms share electrons. Compounds are represented by chemical formulas such as water, H2O.

Mixtures A mixture is material that contains two or more substances that are not chemically combined. The substances in a mixture keep their individual properties. The atmosphere is a mixture of gases. A solution is a mixture in which one substance is uniformly dispersed in another substance such as salt water. An alloy is a solution of two or more metals such as brass, a mixture of copper and zinc and bronze which is a mixture of copper and tin.

Section 2.2 Minerals

Mineral Characteristics A mineral has the following characteristics: Naturally Occurring Solid substance Orderly Crystalline Structure Definite Chemical Composition Inorganic

Processes the form Minerals Crystallization from Magma Precipitation Changes in Pressure and Temperature Formation from Hydrothermal Solutions

Mineral Groups Common minerals, together with the thousands of others that form on Earth, can be classified into groups based on their composition. Silicates are the most abundant group of elements on Earth. They make up more than 90% of the Earth’s crust. Silicon and Oxygen are the most abundant elements on Earth’s surface. They combine to form a structure called a silicon-oxygen tetrahedron.

Mineral Groups Carbonates are minerals that contain the elements carbon, oxygen, and one or more other metallic elements. Calcite is an example. Oxides are minerals that contain oxygen and one or more other element, which are usually metals. Hematite is an example. Sulfates and Sulfides are minerals that contain the element sulfur. Galena is an example. Halides are minerals that contain a halogen ion plus one or more other elements. Halite (NaCl) is an example.

Mineral Groups Native Elements are minerals that only contain one element or type of atom. Gold (Au), Silver (Ag), copper (Cu), sulfur (S), and carbon (C) are examples.

Section 2.3 Properties of Minerals Color Streak – the color of a mineral in its powdered form. It is obtained by rubbing a mineral across a streak plate. Luster – how light is reflected from the surface of a mineral. Examples include metallic, nonmetallic, glassy, earthy, brilliant, etc. Crystal form – the visible expression of a mineral’s internal arrangement of atoms. There are six distinct crystal systems.

Properties of Minerals Hardness – the measure of the resistance of a mineral to being scratched.

Properties of Minerals Cleavage – the tendency of a mineral to cleave, or break, along flat, even surfaces. Fracture – the uneven breakage of a mineral. Density – the ratio of an objects mass to its volume. You need a scale or balance to find the mass, and you need a graduated cylinder or beaker to find the volume. Some minerals can be recognized by other distinctive properties, such as feel, smell, magnetism, double refraction, fizzing from an acid test (calcite), etc.