Chapter Four Chemical Bonding

Lesson 4-1 Ionic Bonds

4-1 Ionic Bonds When atoms have fewer than four valence electrons, they can transfer these to other atoms that have more than four valence electrons. In this way, atoms become more stable. An ion is an atom or group of atoms that has an electrical charge. When an atom loses an electron, it loses a negative charge and becomes a positive ion. When an atom gains an electron, it gains a negative charge and becomes a negative ion. An ionic bond is the attraction between oppositely charged ions.

–For example: A sodium atom reacts with a chlorine atom by losing its one valence electron to chlorine. The sodium atom becomes a positive atom (Na+). The chlorine atom becomes a negative chloride ion (Cl-). The oppositely charged ions attract each other – forming a compound sodium chloride – table salt.

4-1- Ionic Bonds Compounds are electrically neutral. When ions come together, they do so in a way that balances out the charges on the ions.

Example Magnesium ions have a charge of 2+. Chloride ions have a charge of 1-. When they react – the resulting compound has two chloride ions for every one magnesium ion. The compound is Magnesium Chloride (MgCl 2 ).

4-1 Ionic Bonds Poly-atomic ions are ions made of more than one atom. Each poly-atomic ion has an overall positive or negative charge. For example, the carbonate ion (CO 3 2- ) is made of one carbon atom and three oxygen atoms. It has an overall charge of 2-. This ion can combine with a calcium ion (Ca 2+ ) to form the compound calcium carbonate (CaCO 3 ).

4-1 (Ionic Bonds) Naming Ionic Compounds The name of an ionic compound consists of the name of the positive ion followed by the name of the negative ion. If the negative ion is a single element, the end of its name changed to ide. –For example: MgS Mg (Positive Ion) = Magnesium S (Negative Element) Single element – Sulfur Magnesium Sulfide.

You Try NH 4 Cl Hint: NH 4 = Ammonium And is the + Ion.

Answer -You Try NH 4 Cl Ammonium Chloride

4-1 Ionic Bonding The characteristic properties of ionic compounds include: –Crystal shape –High melting point –Electrical conductivity. Positive and negative ions form an orderly, three- dimensional arrangement called a crystal.

Lesson 4-2 Covalent Bonds

4-2 A chemical bond formed when two atoms share electron is called a covalent bond. Covalent bonds often occur between nonmetals. In a covalent bond, both atoms attract the two shared electrons at the same time.

4-2 Double Bond Some atoms share two pairs of electrons, forming a double bond. –Oxygen Bond

4-2 Covalent Bond Some atoms pull more strongly on the shared electrons than other atoms do. As a result, the electrons move closer to one atom, causing the atoms to have slight electrical charges. A polar bond is a covalent bond in which electrons are shared unequally. A non-polar bond is a covalent bond in which the valence electrons are shared equally. The atoms pull equally on the electrons.

4-3 Crystal Chemistry

Properties of Minerals Five Characteristic to being a mineral: –Naturally occurring –Inorganic: does not come from a living substance. –Solid –Crystal structure – repeating crystal patterns. –Definite chemical composition – contains certain elements in definite amounts. Element: a substance composed of a single kind of atom. Compound: two or more elements combined. Mixture: consists of two or more substances that are mixed together but not chemically combined.

Mohs Hardness Scale The Mohs Hardness Scale ranks ten minerals from softest to hardest. –Color: minerals unique characteristic can be used to identify the mineral. For example, a garnet is a deep red stone. –Streak: the color of the minerals powder. –Luster: how a mineral reflects light from its surface – its shine. –Cleavage: a mineral that splits easily along flat surfaces. –Fracture: how a mineral looks when it breaks apart in an irregular way. –Fluorescence: minerals that glow under ultraviolet light.

How Minerals Form Minerals form in two ways: –Crystallization of melted materials. –Crystallization of materials dissolved in water. Crystallization is the process by which atoms are arranged to form a material with a crystal shape.

How Minerals Form Minerals form as hot magma cools deep inside the crust, or as lava hardens on the surface. When the liquids cool, they form mineral crystals. The size of the crystals depend on: –1. The rate at which magma cools. –2. The amount of gas magma contains. –3. The chemical composition of magma.