Chemical Bonding

CHEMICALCHEMICAL BONDINGBONDING 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+ + e-

Mg:  Mg2+ + 2e-

Atoms 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:

- 2- :O: + 2e  :O:

Write 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. 2- e.g. SO3 ion contains covalent bonds between the S and O atoms. But 2- SO3 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)

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.

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 + H2O 

Polar vs. Nonpolar Molecules While a bond may be polar, the shape of a molecule may contribute to an overall nonpolar molecule.

Linear Tetrahedral Bent Pyramidal

CO2 CF4 H2O 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 

IONIC COVALENT

NO YES 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 Primary Hardness Conductivity Melting Examples substance IMF Point 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: ______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