Ionic Bonding, Ionic Compounds, and Metallic Bonding ...
Ionic Bonding, Ionic Compounds, & Metallic Bonding Chemical Bonds Chemical Bond—a mutual electrical attraction between the nuclei and valence electrons of different atoms that binds the atoms together. Chemical Bonds create more stable arrangements of matter. 3 Types of Chemical Bonds 1. Ionic Bonds 2. Covalent Bonds a. Polar Covalent Bonds b. Nonpolar Covalent Bonds 3. Metallic Bonds Ionic Bonding Cation—a positive ion. An atom that has lost electrons. (metals form cations) Oxidation—loss of electrons (becoming positively charged) Anion—a negative ion. An atom that has gained electrons. (nonmetals usually form anions) Reduction—process of gaining electrons (becoming negatively charged) “OILRIG”—Oxidation Is Loss, Reduction Is Gain Ionic Bonding—chemical bonding that results from the electrical attraction between large numbers of cations and anions. (value 1.7-‐3.3)
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Nonpolar Covalent Bond—a covalent bond in which the bonding electrons are shared equally, resulting in a balanced distribution of electrical charge (value 0-‐0.3).
Polar Covalent Bond—covalent bond in which the unbonded atoms have an unequal attraction for the shared electrons (value 0.3-‐1.7). Calculating Bond Type—subtract electronegativities The Octet Rule Atoms can fill their outermost s and p sublevels by sharing electrons through covalent bonding. Such bond formation follows the octet rule: Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest energy level. Exceptions to the Octet Rule Exceptions to the octet rule include those for atoms that cannot fit eight electrons, and for those that can fit more than eight electrons. Common exceptions to the octet rule: Phosphorous Boron Hydrogen Electron-‐Dot Notation Electron-‐dot notation is an electron-‐configuration notation in which only the valence electrons of an atom are shown, indicated by dots placed around the element’s symbol.
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Ionic Compounds • An ionic compound is composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal. • Most ionic compounds exist as crystalline solids.
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The strong attraction between ions in an ionic compound gives ionic compounds some characteristic properties: • high melting points • hard but brittle • not electrical conductors in the solid state, because the ions cannot move
Monatomic Ions Many main-‐group elements can lose or gain electrons to form ions. Ions formed from a single atom are known as monatomic ions. Example: To gain a noble-‐gas electron configuration, nitrogen gains three electrons to form N3– ions.
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Some main-‐group elements tend to form covalent bonds instead of forming ions. Examples: carbon and silicon Naming Monatomic Ions Monatomic cations are identified simply by the element’s name. Examples: K+ is called the potassium cation Mg2+ is called the magnesium cation For monatomic anions, the ending of the element’s name is dropped, and the ending -‐ide is added to the root name. Examples: F– is called the fluoride anion N3– is called the nitride anion
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Binary Ionic Compounds Compounds composed of two elements are known as binary compounds. In a binary ionic compound, the total numbers of positive charges and negative charges must be equal. The formula for a binary ionic compound can be written given the identities of the compound’s ions. Example: magnesium bromide Ions combined: Mg2+, Br – Chemical formula: MgBr2
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A general rule to use when determining the formula for a binary ionic compound is “crossing over” to balance charges between ions. Example: aluminum oxide 1) Write the symbols for the ions. Al3+ O2–
2) Cross over the charges by using the absolute value of Al2O3 each ion’s charge as the subscript for the other ion.
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Naming Binary Ionic Compounds The nomenclature, or naming system, or binary ionic compounds involves combining the names of the compound’s positive and negative ions. The name of the cation is given first, followed by the name of the anion: Example: Al2O3 — aluminum oxide Naming Binary Ionic Compounds, Compounds Containing Polyatomic Ions Polyatomic Ion—group of atoms with a charge Many common polyatomic ions are oxyanions—polyatomic ions that contain oxygen.
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Writing Formulas Containing Polyatomic Ions
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The Stock System of Nomenclature Some elements such as iron, form two or more cations with different charges. To distinguish the ions formed by such elements, scientists use the Stock system of nomenclature. The system uses a Roman numeral after the cation to indicate an ion’s charge. Examples: Fe2+ iron(II) Fe3+ iron(III) Metallic Bonding Chemical bonding is different in metals than it is in ionic or covalent compounds. Metallic bonding gives metals the properties of: • Thermal & Electrical Conductivity • Malleability, Ductility, and Durability • Luster • Hardness & Strength
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The Metallic-‐Bond Model Valence electrons are free to move about the metal. • These mobile electrons form a sea of electrons around the metal atoms. • The chemical bonding that results from the attraction between metal atoms and the sea of electrons is called metallic bonding. • Metallic bonds only exist between atoms of two different metals or atoms of the same metal element.
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Alloys—mixture of elements with metallic properties.
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Nonpolar Covalent Bond—a covalent bond in which the bonding electrons are shared equally, resulting in a balanced distribution of electrical charge (value 0-‐0.3).
Polar Covalent Bond—covalent bond in which the unbonded atoms have an unequal attraction for the shared electrons (value 0.3-‐1.7). Calculating Bond Type—subtract electronegativities The Octet Rule Atoms can fill their outermost s and p sublevels by sharing electrons through covalent bonding. Such bond formation follows the octet rule: Chemical compounds tend to form so that each atom, by gaining, losing, or sharing electrons, has an octet of electrons in its highest energy level. Exceptions to the Octet Rule Exceptions to the octet rule include those for atoms that cannot fit eight electrons, and for those that can fit more than eight electrons. Common exceptions to the octet rule: Phosphorous Boron Hydrogen Electron-‐Dot Notation Electron-‐dot notation is an electron-‐configuration notation in which only the valence electrons of an atom are shown, indicated by dots placed around the element’s symbol.
Image Source: http://www.middleschoolchemistry.com/img/content/multimedia/chapter_4/lesson_6/lewis_dot_table_big.jpg
Ionic Compounds • An ionic compound is composed of positive and negative ions that are combined so that the numbers of positive and negative charges are equal. • Most ionic compounds exist as crystalline solids.
•
The strong attraction between ions in an ionic compound gives ionic compounds some characteristic properties: • high melting points • hard but brittle • not electrical conductors in the solid state, because the ions cannot move
Monatomic Ions Many main-‐group elements can lose or gain electrons to form ions. Ions formed from a single atom are known as monatomic ions. Example: To gain a noble-‐gas electron configuration, nitrogen gains three electrons to form N3– ions.
Image Source: http://preparatorychemistry.com/images/monatomic_ions_PT_CS.jpg
Some main-‐group elements tend to form covalent bonds instead of forming ions. Examples: carbon and silicon Naming Monatomic Ions Monatomic cations are identified simply by the element’s name. Examples: K+ is called the potassium cation Mg2+ is called the magnesium cation For monatomic anions, the ending of the element’s name is dropped, and the ending -‐ide is added to the root name. Examples: F– is called the fluoride anion N3– is called the nitride anion
Image Source: http://www.chem.uwec.edu/Chem103_F08_F0F/pages/resources/media/monoatomic_ions_Silberberg_table_2.3.jpg
Binary Ionic Compounds Compounds composed of two elements are known as binary compounds. In a binary ionic compound, the total numbers of positive charges and negative charges must be equal. The formula for a binary ionic compound can be written given the identities of the compound’s ions. Example: magnesium bromide Ions combined: Mg2+, Br – Chemical formula: MgBr2
Image Source: http://media.wiley.com/Lux/76/167976.image0.jpg
A general rule to use when determining the formula for a binary ionic compound is “crossing over” to balance charges between ions. Example: aluminum oxide 1) Write the symbols for the ions. Al3+ O2–
2) Cross over the charges by using the absolute value of Al2O3 each ion’s charge as the subscript for the other ion.
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Naming Binary Ionic Compounds The nomenclature, or naming system, or binary ionic compounds involves combining the names of the compound’s positive and negative ions. The name of the cation is given first, followed by the name of the anion: Example: Al2O3 — aluminum oxide Naming Binary Ionic Compounds, Compounds Containing Polyatomic Ions Polyatomic Ion—group of atoms with a charge Many common polyatomic ions are oxyanions—polyatomic ions that contain oxygen.
Image Source: http://crescentok.com/staff/jaskew/isr/tigerchem/naming/polyions2.gif
Writing Formulas Containing Polyatomic Ions
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The Stock System of Nomenclature Some elements such as iron, form two or more cations with different charges. To distinguish the ions formed by such elements, scientists use the Stock system of nomenclature. The system uses a Roman numeral after the cation to indicate an ion’s charge. Examples: Fe2+ iron(II) Fe3+ iron(III) Metallic Bonding Chemical bonding is different in metals than it is in ionic or covalent compounds. Metallic bonding gives metals the properties of: • Thermal & Electrical Conductivity • Malleability, Ductility, and Durability • Luster • Hardness & Strength
Image Source: http://blogs.scientificamerican.com/lab-‐rat/files/2012/03/metallic-‐bonding.png
The Metallic-‐Bond Model Valence electrons are free to move about the metal. • These mobile electrons form a sea of electrons around the metal atoms. • The chemical bonding that results from the attraction between metal atoms and the sea of electrons is called metallic bonding. • Metallic bonds only exist between atoms of two different metals or atoms of the same metal element.
Image Souce: http://www.bbc.co.uk/staticarchive/4e6786539008e5012ff9c723c4255ae6fc6c1b9f.gif
Alloys—mixture of elements with metallic properties.
Image Source: http://intranet.micds.org/upper/science/chem_02/chem_text_'02/secondsemester/newchaps/solutionscolligativeprops/images/brass.gif
