Chemistry: Ionic and Metallic Bonding

Why are alloys important?

Alloys are important because their properties are often superior to those of their component elements.

What is the electrical charge of an ionic compound?

Although they are composed of ions, ionic compounds are electrically neutral.

How are anions formed?

An anion is produced when an atom gains one or more valence electrons.

Ionic Compound

- A compound composed of cations and anions. - The total positive charge of the cations equals the total negative charge of the anions.

How are cations formed?

- A positively charged ion, or a cation, is produced when an atom loses one or more valence electrons.

Anions

- An anion is an atom or group of atoms with a negative charge. * # p+ < # e- - Anions are formed when electrons are GAINED. - The name of an anion of a nonmetallic element is NOT the same as the element name. * The name if the anion typically ends in -ide Ex. A chlorine atom (Cl) forms a chloride anion (Cl-), and an oxygen atom (O) forms an oxide anion (O2-) - Atoms of nonmetallic elements attain noble-gas configurations more easily by gaining electrons than by losing them because these atoms have relatively full valence shells. Ex. Chlorine belongs to Group 7A (the halogen family). Atoms of chlorine have seven valence electrons. A gain of one electron gives a chlorine atom an octet and converts a chlorine atom into a chloride ion. Ex. Cl 1s^2 2s^2 2p^6 3s^2 3p^5 --+electron--> Cl- 1s^2 2s^2 2p^6 3s^2 3p^6 = Octet Ex. ar 1s^2 2s^2 2p^6 3s^2 3p^6 = Cl- 1s^2 2s^2 2p^6 3s^2 3p^6 = Octet - Chlorine atoms, therefore, ned one more valence electron to achieve the electron configuration of the nearest noble gas. - The ions produced when atoms of chlorine and other halogens gain electrons are called halide ions. - All halogen atoms have seven valence electrons and need to gain only one electron to achieve the electron configuration of a noble gas. Thus, all halide ions (F-, Cl-, Br-, and I-, ) have a charge of 1-.

Formation of Ions

- An atom is electrically neutral because it has to equal the numbers of protons and electrons. p+ = e- - An ion forms when an atom or group of atoms loses or gains electrons. # p+ ~ # e- - Note that for metals, the name of the cation is the same as the name of the element. Ex. A sodium atom (Na) forms a sodium cation (Na+). Ex. Calcium atom (Ca) forms a calcium cation (Ca^2+). * Although their names are the same, metals and their cations have many important chemical differences. Ex. Sodium metal reacts explosively with water. By contrast, sodium cations are quite nonreactive. Sodium cations are a component of table salt, a compound that is very stable in water.

Ionic Bonds

- Anions and cations have opposite charges and attract one another by means of electrostatic forces. The electrostatic forces that hold ions together in ionic compounds are called ionic bonds. - STRONGEST BOND that exists - Traits of Ionic Compounds: 1. ALL solids at room temp (mostly white powders) 2. High melting points due to strong ionic bond 3. Good conductors when dissolved or melted 4. MUST BE ELECTRICALLY NEUTRAL 5. MUST be written as a formula unit (FU): lowest while number ratio. - Formula Unit: (If you can reduce the SUBSCRIPT, you must reduce). Ex. The sodium atom has a single valence electron that it can easily lose. (If the sodium atom loses its valence electron, it achieves the stable electron configuration of neon.) The chlorine atom has seven valence electrons and can easily gain one electron. (If the chlorine atom gains a valence electron, it achieves the stable electron configuration of argon). When sodium and chlorine react to form a compound, the sodium atom transfers its one valence electron to the chlorine atom. Thus, sodium and chlorine atoms combine in a one-to-one ration, and both ions have stable octets.

Cations

- Any atom or group of atoms with a "+" charge * # p+ > # e- (only applies to metals 80% - ALWAYS form Cations). - Cations are formed when e- are LOST - Cations' names doesn't change Ex. Al = Aluminum atom Al3+ = Aluminum ion - Cation symbol indicates the charge: Na+ Ca2+ - The most common cations are those produced by the loss of valence electrons from metal atoms. Most of these atoms have one to three valence electrons, which are easily removed. Ex. Sodium (atomic number 11) is in Group 1A of the periodic table. Sodium atoms have a total of eleven electrons, including one valence electron. A sodium atom can lose an electron to become a positively charged sodium ion. The sodium ion has an electron configuration that is identical to the noble gas neon. When forming a compound, a sodium atom loses its one valence electron and is left with an octet (eight electrons) in what is now its highest occupied energy level. The number of protons in the sodium nucleus is still eleven, so the loss of one unit of negative charge produces a cation with a charge of 1+. Ex. Na 1s^2 2s^2 2p^6 3s^1 --electron--> Na+ 1s^2 2s^2 2p^6= Octet Ex. Ne 1s^2 2s^2 2p^6 = Na+ 1s^2 2s^2 2p^6 (Octet) - Both the sodium ion and the neon atom have eight electrons in their valence shells (highest occupied energy levels). - Cations of Group 1A elements ALWAYS have a charge of 1+, Cations of Group 2A elements ALWAYS have a charge of 2+. this consistency can be explained in terms of the loss of valence electrons by metal atoms. The atoms lose the number of electrons necessary to attain the electron configuration of a noble gas.

Electron Dot Structures

- Are diagrams that show valence electrons in the atoms of an element as dots. - All of the elements within a given group (with the exception of helium) have the same number of electron dots in their structures.

Binary Ionic Compounds

- Composed of ONLY 2 elements 1. Monatomic Cation (metal) Ex. Na+, Fe3+, Ca2+ 2. Nonatomic Anion (nonmetal) Ex. O2-, Cl-, F- * Have to be on both sides of staircase to for ionic bond. Metal + nonmetal *** IONIC COMPOUNDS ARE ELECTRICALLY NEUTRAL SO THE NET CHARGE OF THE CATION AND THE ANION HAS TO EQUAL ZERO.***

Alloys

- Mixtures of two or more elements, at least one of which is metal. - Benefits of alloys: 1. More durable 2. Reduces rust 3. Improve conductivity d. Improve appearance 2. Example of common alloys Ex. Brass = Cu + Zn Bronze = Cu + Sn Sterling Silver = Cu + Ag Steel = Fe + Cr + ? (Determines the type of steel) Cast Iron = Fe + C

Valence Electrons

- Electrons in the highest occupied energy level of an element's atoms. ** The number of valence e- in the representative elements = to the group number (ex. 1A has 1 valence e-) ** - The number of valence electrons largely determines the chemical properties of an element.

Crystalline Patterns of Metals

- Metals are crystalline - Metals that contain just one kind of atom are among the simplest forms of all crystalline solids. - Metal atoms are arranged in very compact and orderly patterns. 1. Body-centered Cubic: a. Total of 9 atoms / 1 atom at each corner of cube and 1 atom in center of cube b. Ex. Cr, Na, K, Fe 2. Face-centered Cubic: a. Total of 14 atoms / 1 atom at each corner of cube and 1 atom on each face of the cube. b. Ex. Au, Al, Pb 3. Hexagonal Close-Packed a. Total of 10 atoms / hexagon with 1 atom in center then a triangle b. Ex. Zn, Mg, Cd

Transition Metals (group B)

- Most have more than one common ionic charge. (Exceptions: Ag+ , Cd2+, Zn2+) - 2 naming systems... 1. Stock System: uses Roman numerals to indicate charge of the metal Ex. Fe2+ = Iron (II) Fe3+ = Iron (III) Cu2+ = Copper (I) Cu2+ = Copper (II) 2. Classical System: Uses suffixes to indicate charge of the metal (-ous: lower charge, -ic: higher charge) Ex. Fe2+ = Ferrous Fe3+ = Ferric Cu+ = Cuprous Cu2+ = Cupic

What are the three properties of ionic compounds?

- Most ionic compounds are crystalline solids at room temperature. - Ionic compounds generally have high melting points. Ionic compounds can conduct an electric current when melted or dissolved in water.

Octet Rule

- Noble gases are nonreactive in chemical reactions. - In 1916, chemist Gilbert Lewis used this fact to explain why atoms form certain kinds of ions and molecules. - Octet Rule: When forming compounds, atoms tend to achieve the electron configuration of a noble gas. - An octet is a set of EIGHT. - Atoms of each of the noble gases (except helium) have eight electrons in their highest occupied energy levels and the general electron configuration of ns^2np^6. - Atoms of metals tend to lose their valence electrons, leaving a complete octet in the nearest-lowest energy level. - Atoms of some nonmetals tend to gain electrons or to share electrons with another nonmetal atom or atoms to achieve a complete octet.

Transitional Metal Cations

- The charges of cations of the transition metals may vary. Ex. An atom of iron may lose two valence electrons, forming Fe2+ cation, or three valence electrons, forming Fe3+ cation. - Some ions formed by transition metals do not have noble-gas electron configurations (ns^2 np^6) and are therefore exceptions to the octet rule. Ex. Silver 1s^2 2s^2 2p^6 3s^2 3p^6 3d^10 4s^2 4p^6 4d^10 5s^1 * To achieve the structure of krypton, which is the preceding noble gas, a silver atom would have to lose eleven electrons. To acquire the electron configuration of xenon, which is the following noble gas, a silver atom would have to gain seven electrons. * If a silver atom loses its 5s^1 electron, forming a positive ion (Ag+), the configuration that results (4s^2 4p^6 4d^10), with 18 electrons in the highest occupied energy level and all of the orbitals filled, is relatively favorable. Such configuration is known as pseudo noble-gas electron configuration. - Other elements that behave similarly to silver are found at the right of the transition metal block of the periodic table. Ex. Copper, gold, cadmium, and mercury.

Metallic Bonds

- The forces of attraction between the free-floating valence electrons and the positively charged metal ions. These bonds hold metals together. - Described as a "sea of electrons" - Allows for many physical traits of metals such as: 1. Ductile (they can be drawn into wires). 2. Malleable (they can be hammered or pressed into shapes). 3. Good conductor (of electric current because electrons an flow freely in the metal).

How can you model the valence electrons of metal atoms?

- The valence electrons of atoms in a pure metal can be modeled as a "sea of electrons". - Metals consist of closely packed cations and loosely held valence electrons rather than neutral atoms. - The valence electrons are mobile and can drift freely from one part of the metal to another.

How do you find the number of valence electrons in an atom of a representative element?

- To find the number of valence electrons in an atom of a representative element, simply look at its group number. Ex. Atoms of the Group 1A elements (Hydrogen, Lithium, Sodium, and so forth) all have one valence electron, corresponding to the 1 in 1A. Ex. Carbon and silicon atoms, in Group4A, have four valence electrons. Ex. Nitrogen and phosphorus atoms, in Group 5A, have five valence electrons, and oxygen and sulfur atoms, in Group 6A, have six. Ex. The Noble gases (Group 8A) are the only exception to the group number rule: Atoms of helium have two valence electrons, and atoms of all of the other noble gases have eight valence electrons.

Naming Compounds

1. Write the name of the cation first 2. Write the name of the anion second (remember: negative ions end with -ide). Ex. NaCl is Na+ Cl- = Sodium chloride