Matter Matters

Lesson Objectives

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

Vocabulary

  • atom
  • atomic mass
  • chemical bond
  • covalent bond
  • electron
  • element
  • hydrogen bond
  • ion
  • ionic bond
  • isotope
  • molecular mass
  • molecule
  • neutron
  • nucleus
  • polar molecule
  • proton

Introduction

Minerals are made up of different chemical elements bound together. Understanding mineral chemistry aids in understanding how minerals form and why they have certain properties.

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, orbit the nucleus at varying energy levels in a region known as the electron cloud.

An introduction to the atom is seen on this Khan Academy video: http://www.khanacademy.org/video/introduction-to-the-atom.

Major parts of an atom, although the electrons are more accurately represented in a cloud. What chemical element is this? (Hint: 3 protons, 3 electrons)

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 may differ in the number of neutrons found in its nucleus. Atoms of an element with differing numbers of neutrons are called isotopes. For example, carbon always has 6 protons but may have 6, 7, or 8 neutrons. This means there are three isotopes of carbon: carbon-12, carbon-13, and carbon-14. How many protons and neutrons make up carbon-12? Carbon-13? Carbon-14?

For a funny view of the chemical elements, check out this Tom Lehrer song: http://www.youtube.com/watch?v=GFIvXVMbII0.

Ions and Molecules

Atoms are stable when they have a full outermost electron valence shell. 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 a negative electrical charge. What is the charge of an ion if the atom loses an electron? An atom with the same number of protons and electrons has no overall charge, so if an atom loses the negatively charged electron, it has a positive charge. 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 Khan 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 masses of all the atoms in the molecule.

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 its electron with another atom, give it away, or receive an electron from another atom.

The joining of ions to make molecules is chemical bonding. There are three main types of chemical bonds:

  • Ionic bond: Electrons are transferred between atoms. An atom of a metal will give one or more electrons to a non-metallic atom.
  • Covalent bond: 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, similar to a magnet (Figure below).
  • Hydrogen bond: These weak, intermolecular bonds are formed when the positive side of one polar molecule is attracted to the negative side of another polar molecule.

A video about chemical bonding, also from Khan Academy: 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.

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

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?