Lesson Objectives

  • Review basic chemistry concepts: atoms, elements, ions and molecules.
  • Understand the types of chemical bonding and how they result in molecules.

Introduction

Minerals are made of different molecules, which are made of different chemical elements. Understanding mineral chemistry aids in understanding how minerals form and why they each have the properties they do.

Atoms and Isotopes

A chemical element is a substance that cannot be made into a simpler form by ordinary chemical means. The smallest unit of a chemical element is an atom. An atom has all the properties of that element. These are the parts of an atom:
  • At the center of an atom is a nucleus made up of subatomic particles called protons and neutrons.
  • Protons have a positive electrical charge. The number of protons in the nucleus determines what element the atom is (Figure below).
  • Neutrons are about the size of protons but have no charge.
  • Tiny electrons, each having a negative electrical charge, move at nearly the speed of light and orbit the nucleus at varying energy levels in a region known as the electron cloud.
An introduction to the atom is seen on this Kahn Academy video: http://www.khanacademy.org/video/introduction-to-the-atom.
Boron atom.
Boron atom.

Major parts of an atom. What chemical element is this? (Hint: 3 protons, 3 electrons)
An atom with the same number of protons and electrons has no charge. Because electrons are minuscule compared with protons and neutrons, the number of protons plus neutrons gives the atom its atomic mass. All atoms of a given element always have the same number of protons but the number of neutrons in its nucleus may differ. Atoms of an element with differing numbers of neutrons are called isotopes. For example, carbon always has 6 protons, but the number of neutrons can be 6, 7, or 8. This means there are three isotopes of carbon: carbon-12, carbon-13, and carbon-14.
For a funny view of the chemical elements, check out this Tom Lehrer song: http://www.youtube.com/watch?v=GFIvXVMbII0&feature=related.

Ions and Molecules

Atoms are stable when they have a full outermost electron energy level. To fill its outermost shell, an atom will give, take, or share electrons. When an atom either gains or loses electrons, this creates an ion. Ions have either a positive or negative electrical charge. What is the charge of an ion if the atom loses an electron? If an ion loses an electron it has a positive charge, because each electron is negatively charged. What is the charge of an ion if the atom gains an electron? If the atom gains an electron, it has a negative charge.
Electron orbitals are described in this Kahn Academy video: http://www.khanacademy.org/video/orbitals.
When atoms chemically bond, they form compounds. The smallest unit of a compound with all the properties of that compound is a molecule. When two or more atoms share electrons to form a chemical bond, they form a molecule. The molecular mass is the sum of the mass of all of a molecule’s atoms.

Chemical Bonding

Ions come together to create a molecule so that electrical charges are balanced; the positive charges balance the negative charges and the molecule has no electrical charge. To balance electrical charge, an atom may share, give, or take one or more electrons from its outer shell.
The joining of ions to make molecules is chemical bonding. There are three main types of chemical bonds:
  • Ionic: Electrons are transferred between atoms. An atom of a metal will give one or more electrons to a non-metallic atom.
  • Covalent: An atom shares one or more electrons with another atom. The sharing of electrons is not always evenly distributed within a molecule. If one atom has the electrons more often than another atom in the molecule, the molecule has a positive and a negative side. It is a polar molecule because it acts a little bit as if it had poles, like a magnet (Figure below).
A great explanation of ionic and covalent bonding is found on this animation: http://www.youtube.com/watch?v=QqjcCvzWwww.
  • Hydrogen: These weak, intermolecular bonds are formed when the positive side of one polar molecule is attracted to the negative side of another polar molecule.
Also from Kahn Academy, a video about chemical bonding: http://www.khanacademy.org/video/ionic--covalent--and-metallic-bonds.
Hydrogen and oxygen share electrons to form water, which is a covalently bonded, polar molecule. Watch this animation to see how it forms: http://www.youtube.com/watch?v=qmgE0w6E6ZI
Demonstrating dipole in a water molecule.
Demonstrating dipole in a water molecule.

Water is a polar molecule. Because the oxygen atom has the electrons most of the time, the hydrogen side of the molecule has a slightly positive charge while the oxygen side has a slightly negative charge.

Lesson Summary

  • An element is a substance that cannot be made into a simpler form by ordinary chemical means. It is made of atoms.
  • An atom’s nucleus contains positively charged protons and neutrally charged neutrons.
  • The nucleus is orbited by negatively charged electrons, found in the electron cloud.
  • An ion is an atom that has gained or lost one or more electrons.
  • Molecules form when electrons are transferred, creating ionic bonds, or when electrons are shared, forming covalent bonds.

Review Questions

  1. How is an atom different from an ion? How is an atom different from an element?
  2. Describe the subatomic particles you learned about in this lesson.
  3. How is a molecule different from an element? Can a molecule be an element?
  4. Think of the smallest unit of water, a molecule of H2O. Which of the vocabulary words in this lesson describe the hydrogen? Which describe the oxygen? Which terms describe the whole H2O unit?
  5. In which type of bonding are electrons shared? In which are they given or taken? Which type of bond is stronger?

Further Reading and Supplemental Links

Vocabulary

proton A positively charged particle in a nucleus. polar molecule A molecule with an unevenly distributed electrical charge. nucleus The center of an atom, made of protons and neutrons. neutron A neutral particle in the nucleus of an atom. molecule The smallest unit of a compound; it is made of atoms. molecular mass The mass of all the atoms in a molecule. isotope A chemical element that has a different number of neutrons. ionic bond A chemical bond in which atoms give or accept electrons. ion An atom with one or more electrons added or subtracted; it has an electrical charge. hydrogen bond A weak intermolecular connection between two polar molecules. element A pure chemical substance with one type of atom. electron Tiny negatively charged particles that orbit the nucleus. covalent bond Electrons shared between atoms. chemical bond The force that holds two atoms together. atomic number The number of protons in an atom. atomic mass The number of protons and neutrons in an atom. atom The smallest unit of a chemical element.

Points to Consider

  • The noble gases all have a full outermost electron level. How do they bind to other molecules?
  • Why don’t electrons fly off into space? Is electrical force the same as the gravitational force that keeps planets orbiting the Sun?
  • Water has a lot of unusual properties: It forms droplets, lightweight insects can land on it, it is less dense in solid form (ice) than in liquid form. Can you link these properties to hydrogen bonding?