6.02 Bonding/Nomenclature

Forming Compounds Compounds are formed when two or more elements combine. Compounds are formed when two or more elements combine. Atoms form compounds to become more stable and lower their potential energy. Atoms form compounds to become more stable and lower their potential energy. Nature favors this lower potential energy. Nature favors this lower potential energy. To become more stable, atoms want their outer orbits filled. To become more stable, atoms want their outer orbits filled. Most atoms need 8 electrons to be stable and full. This is known as the Octet Rule. Most atoms need 8 electrons to be stable and full. This is known as the Octet Rule. Exceptions are Hydrogen and Helium which need just 2. Boron needs only 6. Exceptions are Hydrogen and Helium which need just 2. Boron needs only 6.

Types There are three types of bonds that occur between elements on the periodic table. There are three types of bonds that occur between elements on the periodic table. These three types are: These three types are: Metallic Metallic Ionic Ionic Covalent Covalent

Metallic Metallic bonds result from the chemical attraction between metal cations and a surrounding sea of electrons. Metallic bonds result from the chemical attraction between metal cations and a surrounding sea of electrons. Metallic During this type of bond the electrons are delocalized and are free to move around any atom. During this type of bond the electrons are delocalized and are free to move around any atom. This type of bond occurs between two metals. This type of bond occurs between two metals.

Metallic Strength Metallic bond strength depends on the number of electrons in the electron sea and the charge of the atoms in the sea. Metallic bond strength depends on the number of electrons in the electron sea and the charge of the atoms in the sea. Heat of vaporization is the amount of energy needed to break solid metals bonds completely to form gaseous metal. Heat of vaporization is the amount of energy needed to break solid metals bonds completely to form gaseous metal. The higher the heat of vaporization, the higher the bond strength. The higher the heat of vaporization, the higher the bond strength.

Metallic Characteristics The freedom of the electrons allows metallic bonded compounds to have a very high electric and heat conductivity. The freedom of the electrons allows metallic bonded compounds to have a very high electric and heat conductivity. Metal compounds also have a high malleability and ductility because atoms can slide past one another without breaking bonds. Metal compounds also have a high malleability and ductility because atoms can slide past one another without breaking bonds. malleability and ductility malleability and ductility

Covalent Covalent bonds result from the sharing of electrons pairs between atoms. Covalent bonds result from the sharing of electrons pairs between atoms. Covalent It is the attraction between the p’s in each nucleus and the shared e’s that holds the bond together. It is the attraction between the p’s in each nucleus and the shared e’s that holds the bond together. This type of bond occurs between two nonmetals. This type of bond occurs between two nonmetals. The structure that is formed by a covalent bond is called a molecule. The structure that is formed by a covalent bond is called a molecule. There are polar and nonpolar molecules. There are polar and nonpolar molecules.

Polar Covalent A molecule in which unequal sharing occurs is said to be polar. A molecule in which unequal sharing occurs is said to be polar.molecule The atom with greater attraction has a partial negative charge and the other has a partial positive charge. The atom with greater attraction has a partial negative charge and the other has a partial positive charge. This causes bond polarity between the two atoms. This causes bond polarity between the two atoms.

Non Polar Covalent A molecule in which equal sharing occurs is said to be nonpolar. A molecule in which equal sharing occurs is said to be nonpolar. Because of the equal sharing, there is no bond polarity. Because of the equal sharing, there is no bond polarity.

Diatomic Molecules A diatomic molecule contains only two atoms. A diatomic molecule contains only two atoms.diatomic Gases such as Oxygen, Nitrogen, and Fluorine are found in nature as diatomic molecules. Gases such as Oxygen, Nitrogen, and Fluorine are found in nature as diatomic molecules. These gases form by single or multiple bonds thus affect their properties. These gases form by single or multiple bonds thus affect their properties.

Covalent Strength The distance between two atoms bonded at their minimum potential energy is the bond length. The distance between two atoms bonded at their minimum potential energy is the bond length. Bond energy is the energy required to break the bond and form neutral isolate atoms. Bond energy is the energy required to break the bond and form neutral isolate atoms. As bond length increases, bond energy decreases. As bond length increases, bond energy decreases. A double bond is formed by the sharing of two pairs of electrons, a triple by three. A double bond is formed by the sharing of two pairs of electrons, a triple by three. These multiple bonds become shorter and therefore stronger with each additional bond. These multiple bonds become shorter and therefore stronger with each additional bond.multiple

Covalent Characteristics Molecular compounds have very low melting point and boiling point due to the very weak attraction between atoms. Molecular compounds have very low melting point and boiling point due to the very weak attraction between atoms. Many are gaseous at room temperature. Many are gaseous at room temperature.

Ionic Ionic bonds result from the chemical attraction between cations and anions. Ionic bonds result from the chemical attraction between cations and anions. Ionic These ions are formed as electrons jump from one atom to another to become more stable. These ions are formed as electrons jump from one atom to another to become more stable. This type of bond occurs between a metal and a nonmetal. This type of bond occurs between a metal and a nonmetal.

Polyatomic ions Ionic bonds can also form between metals and polyatomic ions. Ionic bonds can also form between metals and polyatomic ions. A polyatomic ion is two or more nonmetals that are already bonded covalently to one another. A polyatomic ion is two or more nonmetals that are already bonded covalently to one another.polyatomic The polyatomic ion has an overall charge therefore allowing it to bond to the metal. The polyatomic ion has an overall charge therefore allowing it to bond to the metal.

Ionic Strength Ions can form an orderly arrangement called a crystal lattice to lower their potential energy. Ions can form an orderly arrangement called a crystal lattice to lower their potential energy. The arrangement is a balance of all the repulsions between like charged ions and attraction between opposite charged ions. The arrangement is a balance of all the repulsions between like charged ions and attraction between opposite charged ions. Lattice energy is the energy released when one of these crystalline structures are formed from gaseous ions. Lattice energy is the energy released when one of these crystalline structures are formed from gaseous ions. The higher the negative lattice energy, the stronger the bond. The higher the negative lattice energy, the stronger the bond.

Ionic Characteristics Ionic bonds produce compounds with a high melting point and boiling point. Ionic bonds produce compounds with a high melting point and boiling point. Ionic compounds are brittle due to the fact that they form crystal lattices. Any disturbance can break it. Ionic compounds are brittle due to the fact that they form crystal lattices. Any disturbance can break it.lattices Ionic compounds also have the ability to break into ions in a solution. This allows the solution to have increased electrical conductivity. Ionic compounds also have the ability to break into ions in a solution. This allows the solution to have increased electrical conductivity.

Naming and Writing Formulas Different methods of naming and writing are used depending on the type of bond in the compound. Different methods of naming and writing are used depending on the type of bond in the compound. Ionically bonded compounds are named and written using the Stock method. Ionically bonded compounds are named and written using the Stock method. Covalently bonded compounds are named and written using the Greek prefix method. Covalently bonded compounds are named and written using the Greek prefix method.

Stock System Naming Write the full name of the cation (positive ion) first. Write the full name of the cation (positive ion) first. Write the root of the anion (negative ion) followed by an –ide ending. Write the root of the anion (negative ion) followed by an –ide ending. If a transition element is used, a charge must be assigned and written in parenthesis as a roman numeral. If a transition element is used, a charge must be assigned and written in parenthesis as a roman numeral. The charge is determined by finding out what is need to neutralize the compound or create its overall charge. The charge is determined by finding out what is need to neutralize the compound or create its overall charge.

Stock System Writing formula Write the symbol of the cation, followed by anion Write the symbol of the cation, followed by anion Find their oxidation charges on the periodic table and cross the absolute values of each to get the subscripts. Find their oxidation charges on the periodic table and cross the absolute values of each to get the subscripts.

Greek System Greek SystemNaming Write the full name of the least electronegative (bottom left) element first. Write the full name of the least electronegative (bottom left) element first. Write the root of the most electronegative element (top right) second, followed by an –ide ending. Write the root of the most electronegative element (top right) second, followed by an –ide ending. Write a prefix for each element name based on the subscript number. Write a prefix for each element name based on the subscript number. If the prefix for the first element is mono, it does not have to be included in the name. If the prefix for the first element is mono, it does not have to be included in the name.

Greek System Writing formula Write the symbol for the least electronegative element first followed by the most. Write the symbol for the least electronegative element first followed by the most. Write in subscripts by looking at prefixes for each element. Write in subscripts by looking at prefixes for each element.

Polyatomic ions These are some common polyatomic ions and their charges. They need to be memorized. These are some common polyatomic ions and their charges. They need to be memorized.polyatomic NitrateNO 3 - NitrateNO 3 - AcetateCH 3 COO - SulfateSO 4 2- CarbonateCO 3 2- AmmoniumNH 4 +

Naming/Writing with Polyatomic Endings of polyatomic ions cannot be changed when naming. Endings of polyatomic ions cannot be changed when naming. When determining subscripts in formulas, the charge on the overall polyatomic ion is what is used when crossing. When determining subscripts in formulas, the charge on the overall polyatomic ion is what is used when crossing. If more than one polyatomic ion is used, parenthesis must be added around it before any subscripts can be added. If more than one polyatomic ion is used, parenthesis must be added around it before any subscripts can be added. All other rules remain. All other rules remain.