Chemical Bonds PDF

CHEMISTRY FOR ENGINEERS College of Arts and Sciences CHEMICAL BONDS Mick Bryan A. Javonillo Faculty-in-Charge Why and How do atoms combine? CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Chemical Bondi...

CHEMISTRY FOR ENGINEERS College of Arts and Sciences CHEMICAL BONDS Mick Bryan A. Javonillo Faculty-in-Charge Why and How do atoms combine? CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Chemical Bonding A chemical bond is the attractive force that holds two atoms together in a more complex unit. form as a result of interactions between electrons found in the combining atoms. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Lewis Symbol Gilbert Newton Lewis (1875 – 1946) A Lewis symbol is the chemical symbol of an element surrounded by dots equal in number to the number of valence electrons present in atoms of the element frequently called electron-dot structures. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences  The general practice in writing Lewis symbols is to place the first four “dots” separately on the four sides of the chemical symbol and then begin pairing the dots as further dots are added. Three important generalizations about valence electrons can be drawn from a study of the Lewis symbols 1. Representative elements in the same group of the periodic table have the same number of valence electrons. 2. The number of valence electrons for representative elements is the same as the Roman numeral periodic-table group number. 3. The maximum number of valence electrons for any element is eight. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Write Lewis symbols for the following elements. a. O, S, and Se b. B, C, and N CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences The Octet Rule The term stable as used here refers to the idea that a system, which in this case is an arrangement of electrons, does not easily undergo spontaneous change. The valence electron configurations of (helium, neon, argon, krypton, xenon, and radon) are considered the most stable of all valence electron configurations. Helium’s valence electron configuration is 1𝑠 2. All of the other noble gases possess 𝑛𝑠 2 𝑛𝑝6 valence electron configurations CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences  Atoms of many elements that lack the very stable noble-gas valence electron configuration tend to acquire it through chemical reactions that result in compound formation. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Ionic Bonding An ion is an atom (or group of atoms) that is electrically charged as a result of the loss or gain of electrons. An atom’s nucleus never changes during the process of ion formation. The number of neutrons and protons remains constant. A loss of electrons by an atom always produces a positive ion. A gain of electrons by an atom always produces a negative ion. Loss of one, two, or three electrons gives ions with +1, +2, or +3 charges, respectively. A gain of one, two, or three electrons gives ions with -1, -2, or -3 charges, respectively. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences The notation for charges on ions is a superscript placed to the right of the chemical symbol. Some examples of ion symbols are Note that we use a single plus or minus sign to denote a charge of 1, instead of using the notation 1+ or 1-. Also note that in multicharged ions, the number precedes the charge sign; that is, the notation for a charge of plus two is 2+ rather than +2. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Give the chemical symbol for each of the following ions. a. The ion formed when a barium atom loses two electrons b. The ion formed when a phosphorus atom gains three electrons CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Isoelectric Species Isoelectronic species are an atom and ion, or two ions, that have the same number and configuration of electrons. It should be emphasized that an ion that is isoelectronic with a noble gas does not have the properties of the noble gas. It has not been converted into the noble gas. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Lewis Structures for Ionic Compound A Lewis structure is a combination of Lewis symbols that represents either the transfer or the sharing of electrons in chemical bonds. The reaction between the element sodium (with one valence electron) and chlorine (with seven valence electrons) is represented as follows with a Lewis structure oxygen has room for two additional electrons, two sodium atoms are required per oxygen atom—hence the formula Na O. 2 CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences The Structure of Ionic Compound An ionic compound, in the solid state, consists of positive and negative ions arranged in such a way that each ion is surrounded by nearest neighbors of the opposite charge. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Recognizing Binary Ionic Compounds A binary compound is a compound in which only two elements are present. A binary ionic compound is an ionic compound in which one element present is a metal and the other element present is a nonmetal. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Naming Binary Ionic Compounds Binary ionic compounds are named using the following rule: The full name of the metallic element is given first, followed by a separate word containing the stem of the nonmetallic element name and the suffix –ide. The name of the metal ion is always exactly the same as the name of the metal itself; the metal’s name is never shortened The name of an ionic compound never contains any reference to formula subscript numbers. There is only one ratio in which aluminum and sulfur atoms combine. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Names of Selected Common Nonmetallic Ions CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Magnesium Oxide Aluminum Sulfide Potassium Nitride Calcium Chloride CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences When we name compounds that contain metals with variable ionic charges, the charge on the metal ion must be incorporated into the name. This is done by using Roman numerals. A Classical method for indicating the when a metal has two common ionic charge on metal ions uses the charges, the suffix -ous is used for the ion of suffixes -ic and -ous rather than the lower charge and the suffix -ic for the ion of Roman numeral system. higher charge. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Activity Write chemical formulas for the following binary ionic compounds. 1.) Potassium bromide 2.) Silver oxide 3.) Beryllium fluoride 4.) Barium phosphide CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Activity Name the following binary ionic compounds, each of which contains a variable-charge metal. 5.) 6.) 7.) 8.) CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Activity Calculate the charge on the metal ion in the following binary ionic compounds, each of which contains a variable-charge metal. 9.) 10.) 11.) 12.) CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Polyatomic Ions A monatomic ion is an ion formed from a single atom through loss or gain of electrons. A polyatomic ion is an ion formed from a group of atoms (held together by covalent bonds) through loss or gain of electrons. Note that polyatomic ions are not molecules. They never occur alone as molecules do. Instead, they are always found associated with ions of opposite charge. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Generalizations 1. Most, but not all, of these ions carry a negative charge, which can vary from 1− to 3−. There are, however, two positive polyatomic ions in the group: (hydronium) and (ammonium). 2. Most, but not all, of these ions contain oxygen atoms. There are, however, two ions that do not: (cyanide) and (ammonium). 3. Most, but not all, of the negative ions have names that end in -ate. There are, however, two exceptions: hydroxide and cyanide CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Generalizations 4. Two positive ions have names that end in -ium: hydronium and ammonium (NH4 +). 5. A number of pairs of ions exist wherein one member of the pair differs from the other by having a hydrogen atom present, as in (carbonate) and (hydrogen carbonate or bicarbonate). In such pairs, the charge on the ion that contains hydrogen is always 1 less than that on the other ion. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Chemical Formulas and Names for Ionic Compounds Containing Polyatomic Ions CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Two conventions not encountered previously in chemical formula writing often arise when writing chemical formulas containing polyatomic ions. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Determine the chemical formulas for the ionic compounds that contain these pairs CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Name the following compounds, which contain one or more polyatomic ions. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Covalent Bond ❑ is a chemical bond resulting from two nuclei attracting the same shared electrons. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Lewis Structures for Molecular Compounds Fluorine needs only one electron to achieve the octet of electrons that enables it to have a noble-gas electron configuration. When fluorine bonds to other nonmetals, the octet of electrons is completed by means of electron sharing. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences A common practice in writing Lewis structures for covalently bonded molecules is to represent the shared electron pairs with dashes. Using this notation, the H2, HF, F2, and BrF molecules are written as Bonding electrons are pairs of valence electrons that are shared between atoms in a covalent bond. Nonbonding electrons are pairs of valence electrons on an atom that are not involved in electron sharing. - often referred to as unshared electrons pairs or lone electron pairs (or simply lone pairs) CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Draw Lewis structures for the simplest binary compounds that can be formed from the following pairs of nonmetals. a. Nitrogen and iodine b. Sulfur and hydrogen CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Single, Double, and Triple Covalent Bonds ❑ single covalent bond is a covalent bond in which two atoms share one pair of electrons. ❑ double covalent bond is a covalent bond in which two atoms share two pairs of electrons. ❑ triple covalent bond is a covalent bond in which two atoms share three pairs of electrons. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Valence Electrons and Number of Covalent Bonds Formed ❑ Not all elements can form double or triple covalent bonds. There must be at least two vacancies in an atom’s valence electron shell prior to bond formation if it is to participate in a double bond, and at least three vacancies are necessary for triple-bond formation CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Systematic Procedures for Drawing Lewis Structures ❑ Step 1: Calculate the total number of valence electrons available in the molecule by adding together the valence electron counts for all atoms in the molecule. The total number is therefore 6 + 2(6) = 18. ❑ Step 2: Write the chemical symbols of the atoms in the molecule in the order in which they are bonded to one another, and then place a single covalent bond, involving two electrons, between each pair of bonded atoms The central atom is the atom that appears only once in the formula. Carbon is the central atom in nearly all carbon-containing compounds. Neither hydrogen nor fluorine is ever the central atom. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences ❑ Step 3: Add nonbonding electron pairs to the structure such that each atom bonded to the central atom has an octet of electrons. Remember that for hydrogen, an “octet” is only two electrons. At this point, 16 of the 18 available electrons have been used. ❑ Step 4: Place any remaining electrons on the central atom of the structure. Placing the two remaining electrons on the S atom gives CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences ❑ Step 5: If there are not enough electrons to give the central atom an octet, then use one or more pairs of nonbonding electrons on the atoms bonded to the central atom to form double or triple bonds. ❑ Step 6: Count the total number of electrons in the completed Lewis structure to make sure it is equal to the total number of valence electrons available for bonding, as calculated in Step 1. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Draw Lewis structures for the following molecules. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Naming Binary Molecular Compounds Number of Prefix Atoms ❑ When naming, the appropriate prefix is used only if 1 mono- there are more than one atom of that element in the 2 di- formula. 3 tri- ❑ The second element is named after the first, but with 4 tetra- the ending of the element's name changed to -ide. 5 penta- The appropriate prefix is always used for the second 6 hexa- 7 hepta- element. 8 octa- ❑ Do not use “mono-” on the first element. 9 nona- ❑ If you have “ao” or “oo”, turn it into “o” 10 deca- CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Example: CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Activity Write chemical formulas for the compounds formed between the following positive and negative ions. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Activity Name the following compounds, all of which contain polyatomic ions and fixed-charge metals. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences Activity Fill in the blanks to complete the following table of information about selected ionic compounds. The first line of the table is already completed as an example. CHEMISTRY FOR ENGINEERS Department of Mathematics and Natural Sciences