KEY VOCABULARY Atom The basic structural unit of matter; the smallest particle of an element that can enter into a reaction. Bond The electrical attraction between two different atoms (elements) that forms a molecular or ionic compound. Chemical bond The electrical attraction between two different atoms (elements) that forms a molecule (compound) Chemical formula A shorthand notation to describe elements and compounds and their reactions. Each element is identified by one or two letters. For example, H represents hydrogen, Cl represents chlorine, and O represents oxygen. Compound Covalent bonds Chemical bonds in which atoms share electrons. Element A collection of atoms of one type that cannot be decomposed into any simpler units except by spontaneously changing into other units by radioactive processes. Oxygen, hydrogen, iron, and carbon are examples of elements.

Ion An atom or group of atoms that has gained or lost one or more electrons and is now either positively or negatively charged. ionic bond A bond that forms when electrons are transferred from one atom to another, resulting in two oppositely charged ions that now attract each other. Molecule The smallest particle of an element or compound that displays the properties of the substance in quantity.

Atoms and Molecules An atom is defined as the smallest particle of an element that retains the properties of the element. Elements are the simplest chemical forms of matter: they cannot be broken down into simpler substances by chemical processes. The 90 naturally occurring elements are listed in the Periodic Table of the Elements. A molecule consists of two or more atoms that are held together through covalent bonds. Some elements and all covalent compounds are made of molecules. Most of the elements that are commonly found in molecular form are diatomic—their molecules contain two identical atoms. This activity involves three elements—hydrogen, oxygen, and nitrogen. Types of Substances A compound is a substance that consists of two or more elements chemically combined through bonding. There are two major classes of compounds: molecular and non-molecular. In covalent bonds, atoms share electrons. The bond between two identical atoms, such as the bonds in H2, O2, and N2, are pure, non-polar covalent bonds. Other bonds between non-metal elements, such as the bond between oxygen and hydrogen in water, involve a more or less unequal sharing of electrons. These bonds are called polar covalent bonds.

In contrast to a covalent bond is an ionic bond. In an ionic bond, electrons are transferred Or donated from one atom to another. The atoms that have gained or lost electrons are no longer neutral and are now called ions. (An ion is an atom or group of atoms that has a positive or negative charge.) Ionic bonds form from an electrostatic attraction between the positive and negative ions.

In your science notebook, write what you think the formula for this molecule would be. In your science notebook, draw and label a diagram of your model of an oxygen molecule.

In your science notebook, write what you think the formula for this molecule would be. In your science notebook, draw and label a diagram of your model of an nitrogen molecule. N 2 nitrogen

In your science notebook, write the name and chemical formula each molecule in the table above. Use your materials to create a model of each molecule, then draw and a sketch of each. Water Methanol Ethanol

Four—carbon, hydrogen, oxygen, and nitrogen. They are the sites where the atom can make a bond with another atom. It stands for the number of hydrogen atoms in the molecule.

An element is a substance that is composed of only one type of atom. This describes carbon, hydrogen, nitrogen, and oxygen. A compound is any substance composed of two or more elements chemically bonded together. Water and ethanol both have two or more elements chemically bonded together, so they are compounds.

Both are made of the same three elements and both contain an OH and a CH 3. Methanol contains one carbon atom. Ethanol contains two carbon atoms, and so it has more of a chain structure than methanol does. The formula CH 3 OH better describes the structure of the methanol molecule. From the formula CH 4 O, you can’t tell how the oxygen atom is involved in bonding without constructing a model.

You could also write ethanol’s formula as C 2 H 6 O or as CH 3 CH 2 OH. The notation C 2 H 6 O gives the correct number of each kind of atom in a molecule of ethanol, but it doesn’t communicate anything about structure. CH 3 CH 2 OH is long, but it most clearly suggests the structure of the molecule.

Water and the alcohols are similar in that they all include hydrogen and oxygen in OH groups. But the alcohols have carbon while oxygen does not, and they have larger molecules.