A basic understanding of chemistry will become increasing important as we study sediments and eventually seawater.

Why do you need to know Chemistry?

The Earth, including the oceans, is made of matter. The interaction of matter and energy drives the Earth (and indeed, the known universe!). Thus, matter matters! Chemistry is simply the study of matter and its interactions, thus chemistry must matter!

Matter is Made of Atoms

Matter is composed of atoms. Millions/Billions of repeating similar atoms make up a particular substance. All atoms are made up of subatomic particles and each atom has a particular structure. There are three subatomic particles; Proton, Neutron and Electron. The proton has a positive charge, a neutron has no charge, and an electron has a negative charge. the protons and neutrons are located in the nucleus. The nucleus has the most mass of the atom. The electron cloud is outside of the nucleus and contains the most space of an atom. The diagrams you will see are typically not drawn to scale.

Elements

Protons determine the positive charge of the nucleus. All atoms with the same number of protons will behave in the same way. The number of protons in an atom is called the Atomic Number. An Element consists of all atoms with the same atomic number (same # of protons). Each element is given a unique name represented by a unique symbol The symbol is a single capitol letter or a capitol letter plus a lower case letter. Many symbols are fairly obvious; like O stands for oxygen or Cl stands for chlorine. Some elements were known to the ancient Romans, and thus their symbols refer to the Latin names of the elements. Some examples are: Na stands for natrium, what we know as sodium (where do you find sodium in the oceans?)and Cu is cuprum or copper, while Co is the symbol for cobalt.

What Element is This?

In this schematic atom from one of NASA’s websites, the protons are yellow and the neutrons are red. The Atom Number is 4, there are 5 neutrons and there are 4 electrons. This element is Beryllium.

Periodic Table of the Elements

The known elements are listed by their atomic numbers in the periodic table. Typical periodic tables (Like the one in your textbook) will give the element's symbol in the middle, atomic number on the top, and the atomic mass on the bottom. The period table has rows (horizontal) and columns (up and down). Click on Chemical Elements (Links to an external site.) to go a website version of the periodic table. This website gives an abundance in information on the periodic table and the elements (click on the element).

Atomic Mass

The Atomic Mass is listed in the bottom of the elemental box. This mass was calculated by adding the number of protons to the number of neutrons. The total is the Atomic Mass. If you notice that the numbers are not whole numbers, this is because it is an average (taking into account isotopes). What is the atomic mass for the beryllium atom (pictured above)? It is 9 (4p + 5n).

Here’s a simple problem illustrating the use of the atomic mass number. You fill a balloon with carbon dioxide (CO₂) gas and release it. Will it rise or sink? (Hint, air is 78% N₂ gas and 21% O₂ gas)

Answer: Use the periodic table to determine the approximate atomic mass number for each of the three gasses. With an atomic mass of 44, CO2 is the heaviest of the three gasses, and the balloon will sink!

Structure of the Electron Cloud

An Orbital is a region around a nucleus that holds a certain number of electrons. Each orbital can only hold a specific number of electrons (the 1st orbital can only hold 2e). Again the diagram above, has two orbitals, with two electrons in the inner orbital and two electrons in the second orbital. For beryllium, the outermost orbital has only two electrons in it even though this orbit can hold 8 electrons. Columns on the periodic table have elements with the same number of outer electrons and rows have the same number of electron orbitals.

Noble gases

Atoms are the most stable when the outermost orbital is full. The noble gases are elements that have their orbits filled and are not involved in chemical reactions. The noble gasses are located on the right-hand side of the periodic table. Check out this website to further investigate the Noble gases. Go back to Chemical Elements (Links to an external site.) to investigate noble gases.

Ions

An ion is an atom or collection of bonded atoms that have an unbalanced number of protons and electrons. Take a look at the element chlorine Chemical Elements (Links to an external site.). Chlorine has 17 electrons. Notes that if chlorine were to get one electron the outer shell would be full. Then chlorine would have 18 electrons and 17 protons (an imbalance of 1 more electron. Thus, an ion of chlorine has a change of -1, or Cl^-1

Now, let's go back to our example of beryllium. In the image above the outer orbital has two electrons but can hold eight. The only way to achieve a filled outer orbital is to remove electrons from the outer shell.

Now take a look at the image below. The outer orbital is full of electrons (2), and is thus stable. However the atom no longer has an equal number of protons and electrons. It is now electrically unbalanced, and has become an ion. In our example, the beryllium atom has four positively charged protons and two negatively charged electrons. The ion has a charge of +2, and is written Be⁺².

To further understand the definition of ions check out this definition of ion and other related definitions at Wikipedia Ion. (Links to an external site.)

Valence Numbers

The number of electrons an atom takes, gives up, or shares to form atomic bonds is called the valence number. The valence number for beryllium is +2 and the valence number for chlorine is -1.

What would be the valence number for Hydrogen? or Oxygen? Hydrogen is located in the 1st columns and has one electron in its outer orbit. It will most likely lose one electron and the valence number would be +1. Oxygen has 6 electrons in its outer orbit and is likely to gain two electrons. The valence for oxygen would be -2 (2 more negative electrons than protons).

Atomic bonds

When atoms link together they for a type of atomic bond. There are different types of atoms bonds (ionic, covalent, metallic, etc.). Ionic bonds the negative ions will be attracted to positive ions. Continuing our example, it would take two Cl^-1 ions to balance one Be⁺² ion, so these ions would bond in a proportion of 2-1. The molecule beryllium chloride thus has a formula of BeCl₂ Atomic bond are drawn with lines to show the angle of the bond and the type of bond. Take a look hat how water is bonded together. Water Structure and Science (Links to an external site.) Notice the ratio of hydrogen to oxygen 2:1.

Molecules

Molecules consist of 2 or more atoms bonded together. The molecule must be electronically balanced (neutral). The subscripts of the molecule indicate how many atoms of that particular element. Water is a molecule (H₂O). How many hydrogen and oxygen atoms. Salt (NaCl) is also a molecule. Salt is very important to the study of oceanography, check out this website on salt. The Salt Institute. (Links to an external site.)

Is (CO3)^-2 a molecule? No, it is a complex ion. Look at the Superscript (-2) indicating that it is a charged molecule.