Chapter 2.1

 Why do we care about chemistry in Earth Science?  The earth is made up of rocks and minerals.  Rocks and minerals are made of elements.  An element is a substance that cannot be broken down into a simpler substance by chemical or physical means.

 Elements are made up of atoms.  An atom is the smallest particle of matter that contains the characteristics of an element.  The center of an atom is called the nucleus.  The nucleus is made up of particles called protons and neutrons.  Particles called electrons surround the nucleus.

 Protons are positively charged and weigh approximately 1 atomic mass unit or (amu).  Neutrons have no charge and weigh approximately 1 atomic mass unit or (amu).  Electrons are negatively charged but they have hardly any mass at all.

 Atoms of any element always have a specific number of protons that doesn’t change.  The number of neutrons however, can vary.  An atom that has the same number of protons but a different number of neutrons is referred to as an isotope.

 A compound is a substance that consists of two or more elements that are chemically combined in specific proportions.

 Atoms have energy levels (sometimes called shells) that contain electrons.  The first energy level can hold 2 electrons.  The outer energy levels hold 8 electrons.  If an atom’s outer energy levels are not full, they will chemically combine or react with other atoms to make their shells full.  After the reaction is complete, the atoms are combined to form compounds.

 When elements chemically combine to form a compound it is called bonding.  Ionic bonds form between positive and negative ions, when one ion gives up an electron and another ion receives an electron.  An ion is an atom that has an electrical charge because of a gain or loss of one or more electrons.

 Sodium (Na + ) and Chlorine (Cl - ) are both ions that form an ionic bond to make Sodium Chloride (NaCl).  Sodium has one electron in its outer shell that it loses to become positively charged. Chlorine has seven electrons so it gains an electron from sodium to become negatively charged.

 When atoms do not give up or receive atoms, another way to chemically combine is to share electrons.  When atoms share rather than give or receive electrons it is referred to as a covalent bond.  Water is a good example of a covalent bond.

 And lastly, another common type of chemical bond that occurs with earth’s rocks and minerals are metallic bonds.  Metallic bonds are similar to covalent bonds in that the electrons are shared, but unlike the electrons in a covalent bond, electrons in a metallic bond can move freely through a metal.  This gives metals their unusual properties like having the ability to conduct electricity, and being malleable and ductile.