CHEMICAL BONDING Text Book Chapters 7, 8, 9 OBJECTIVES Explain chemical bonding in terms of the behavior of electrons Major Understandings: Chemical bonds are formed when valence electrons are: - transferred from one atom to another (ionic) - shared between atoms (covalent) - mobile within a metal (metallic) Atoms attain a stable valence electron configuration by bonding with other atoms. Noble gases have stable valence configurations and tend not to bond. In a multiple covalent bond, more than one pair of electrons are shared between two atoms. Unsaturated organic compounds contain at least one double or triple bond. Two major categories of compounds are ionic and molecular (covalent) compounds. Metals tend to react with nonmetals to form ionic compounds. Nonmetals tend to react with other nonmetals to form molecular (covalent) compounds. Ionic compounds containing polyatomic ions have both ionic and covalent bonding. When a bond is broken, energy is absorbed. When a bond is formed, energy is released. Electronegativity indicates how strongly an atom of an element attracts electrons in a chemical bond. Electronegativity values are assigned according to arbitrary scales. The electronegativity difference between two bonded atoms is used to assess the degree of polarity in the bond. Molecular polarity can be determined by the shape of the molecule and distribution of charge. Symmetrical (nonpolar) molecules include CO2, CH4, and diatomic elements. Asymmetrical (polar) molecules include HCl, NH3, and H2O. Intermolecular forces created by the unequal distribution of charge result in varying degrees of attraction between molecules. Hydrogen bonding is an example of a strong intermolecular force. Physical properties of substances can be explained in terms of chemical bonds and intermolecular forces. These properties include conductivity, malleability, solubility, hardness, melting point, and boiling point. A chemical bond is the force that holds molecules together. Different types of bonds account for different properties observed in diverse substances. Octet Rule = In forming compounds, elements tend to achieve the electron configuration of a noble gas. When a chemical bond is formed, the resulting compound has less potential energy that the substances from which it was formed. This energy is always released when bonds are formed. Therefore, making a chemical bond is considered ______________________. (Energy is a product and is released) Energy is required to overcome the attractive forces of these bonds. Therefore, breaking bonds is ____________________. (Energy is a reactant and is absorbed) 1. To break a chemical bond, energy must be a) absorbed b) destroyed c) produced d) released 2. In the following balanced equation representing a reaction: 2NaCl 2Na + Cl2 the bonds are: a) formed and energy is absorbed b) formed and energy is released c) broken and energy is absorbed d) broken and energy is released IONIC BONDING When a metal transfers an electron to a nonmetal Atoms of the metallic elements tend to _______ their valence electrons, leaving a complete octet in the next-lowest energy level. A loss of an electron produces a _____________ (positively charged ion) Na. Na+ + eMg: Mg2+ + 2eAtoms of the nonmetallic elements tend to ___________ electrons or to share electrons with another nonmetallic element to achieve a complete octet. The gain of negatively charged electrons by a neutral atom produces an ________ .Cl: + e- :Cl: :O: + 2e- :O: 2Write the equation for the formation of the ion formed when: 1. A potassium atom loses one electron 2. A zinc electron loses two electrons 3. A fluorine atom gains one electron 4. A hydrogen atom gains one electron 5. A hydrogen atom loses one electron Ionic Bond = Compounds composed of cations and anions are called ____________________ Although they are composed of ions, ionic compounds are neutral. The oppositely charged ions will be attracted together in ratios such that their net charge is zero. Na. + .Cl: 1 positively charged sodium ion will balance with 1 negatively charged chlorine ion Mg: + .Cl: 1 positively charged magnesium ion is balanced with 2 negatively charged chlorine ions Al + Br 1 positively charged aluminum ion is balanced with 3 negatively charged bromine ions Polyatomic Ions = covalently bonded but form ionic bonds with other ions. e.g. SO32- ion contains covalent bonds between the S and O atoms. But SO32- will form an ionic bond with Mg Mg SO3 SWAP AND DROP find the charges on the individual ions and swap and drop them to figure out the formula of the product. Predict the ionic compounds formed from the following elements: Potassium and oxygen Magnesium and sulfur Aluminum with oxygen NAMING IONIC COMPOUNDS To name a binary ionic compound place the _______ name first, followed by the _________ name with an _______ ending. Note: Polyatomic ions keep their names as is. (see Table E) NaBr Cs2O Strontium Fluoride Barium Iodide Working with elements with more than one possible oxidation state If more than one oxidation state is possible for an element, the name of the compound must include the oxidation state in (roman numerals) immediately following the element. CuO SnF2 Iron (III) Oxide Tin (IV) Sulfide COVALENT BONDING When 2 or more nonmetals share electrons. Covalent Bond = A bond formed by the sharing of electron pairs between Note: Although almost every element is looking for a stable octet, Hydrogen & Helium are stable with 2 electrons (not 8). H + :Cl: H + O Multiple Bonds Single Bonds = 1 pair of shared electrons Double Bonds = 2 pair of shared electrons Triple Bonds = 3 pair of shared electrons Polar vs. Nonpolar bonds (Dipoles) Nonpolar covalent bond = __________ sharing between two similar atoms Polar covalent bond = _______________ sharing between dissimilar atoms. Electrons move closer to the more electronegative atom. Coordinate covalent bond = when one atom contributes _______________ ____________________ in the shared pair H+ + NH3 H+ + H 2O Polar vs. Nonpolar Molecules While a bond may be polar, the shape of a molecule may contribute to an overall nonpolar molecule. Linear CO2 Tetrahedral CF4 Bent H2O Pyramidal NH3 Common molecules worth knowing H2O CH4 CO2 NH3 O2 N2 NAMING COVALENT COMPOUNDS Covalent compounds use prefixes (mono, di, tri, tetra) to indicate multiple atoms of the same element. (NO MONO IS NEEDED ON THE CATION) Write the name from the given formula SO2 SO3 Write the formula from the given name Carbon Tetrachloride Carbon Dioxide NAMING A BINARY COMPOUND 1. [name of Cation] [name of Anion] change ending to –ide Note: Polyatomic ions keep their names as is. (see Table E) 2. Is the compound ionic? If yes go to #3 Is the compound covalent? If yes go to #4 3. Does the cation have more than one possible oxidation state? NO = name is complete YES = the name of the compound must include the oxidation state in (roman numerals) immediately following the element. name is complete 4. Use prefixes (mono, di, tri, tetra) to indicate multiple atoms of the same element. Note: No prefix is needed on the cation if there is only 1 of them. name is complete [name of Cation] [name of Anion] change ending to –ide Note: Polyatomic ions keep their names as is. (see Table E) IONIC COVALENT Does the cation have more than one possible oxidation state? NO name is complete Use prefixes (mono, di, tri, tetra) to indicate multiple atoms of the same element. Note: No prefix is needed on the cation if there is only 1 of them. YES name of the compound must include the oxidation state in (roman numerals) immediately following the element. METALLIC BONDING Metal atoms are present as ions, with electrons free to move around (mobile electrons). Attraction of these free floating electrons to metal cations is a _____________________________ This structure gives explains many of metals properties including being conductive, malleable and ductile. Alloys = mixtures of two or more elements, one of which is a ___________ Alloys have properties which differ from their constituent elements. e.g. sterling silver (92.5% Ag, 7.5% Cu) is harder and more durable than pure Ag, but still soft enough to be made into jewelry and tableware. Bronze is an alloy of 7:1 Cu:Sn INTERMOLECULAR FORCES OF ATTRACTION Molecules can attract each other by a variety of forces. While intermolecular forces are weaker than either ionic or covalent bonds, they are important. They play a role in determining whether a compound will be solid, liquid or gas. Van der Waals forces Dipole – Dipole when oppositely charged regions of ____________ molecules are attracted to each other Dispersion very weak force, caused by _________________________ (momentary poles) Stronger when more _________________ are present (Halogen examples: F, Cl with relatively few electrons are gases, Br with more electrons is a liquid and I is a solid) Hydrogen bonding attractive force in which a _____________ that is covalently bonded to a highly electronegative atom, is also weakly bonded to an unshared electron pair of another electronegative atom. Strongest of the intermolecular forces e.g. In general, the more polar the bond stronger forces higher melting points (and sometimes boiling points too) TYPES OF SUBSTANCES IONIC COMPOUNDS a 3 dimensional framework of ____________ (table salt) Hardness Conductivity Melting point Example - COVALENT MOLECULAR COMPOUNDS individual covalent molecules ________________________ by intermolecular bonds (sugar) Hardness Conductivity Melting point Example COVALENT NETWORK COMPOUNDS a 3 dimensional framework of ___________ Hardness Conductivity Melting point Example - METALLIC metal ions surrounded by __________________ Hardness Conductivity Melting point Example - Type Particles in substance Primary IMF Hardness Conductivity Melting Point Examples Ionic Covalent molecular Covalent network Metallic 1. The electrical conductivity of KI (aq) is greater than the electrical conductivity of H2O (l) because the KI (aq) contains a) Molecules of H2O c) ions from H2O b) Molecules of KI d) ions from KI 2. Which factor distinguishes a metallic bond from an ionic or covalent bond? a) The mobility of electrons c) the equal sharing of electrons b) The mobility of protons c) the unequal sharing of electrons 3. Which substance has a high melting point and conducts electricity in the liquid phase? a) Ne b) Hg c) NaCl d) CO 4. Which substance is a conductor of electricity? a) NaCl (s) b) NaCl (l) c) C6H12O6 (s) d) C6H12O6 (l) NAME: _______________________________________ BONDING BIG IDEAS FORMULAS REFERENCE TABLES Alloy Bent Coordinate covalent bond Covalent bond Covalent molecular compound Covalent network compound Dipole Dipole-dipole Dispersion Double bond Endothermic Exothermic Hydrogen bond Ionic bond Ionic compound Intermolecular Intermolecular force of attraction Intramolecular Linear Metallic bond Nonpolar covalent bond Nonpolar molecule Polar covalent bond Polar molecule Polyatomic ion Pyramidal Single bond Symmetrical Tetrahedral Triple bond