IV. Chemical Bonding

J Deutsch Compounds can be differentiated by their chemical and physical properties. (3.1dd)

J Deutsch Two major categories of compounds are ionic and molecular (covalent) compounds. (5.2g)  Ionic compounds are formed when a metal combines with a nonmetal.  Ionic compounds have ionic bonds.  Molecular compounds are formed between two nonmetals.  Molecular compounds have covalent bonds.

J Deutsch Regents Question: 06/02 #3 Which compound contains ionic bonds? (1)NO (2)NO 2 (3)CaO (4) CO 2 Nitrogen – nonmetal Oxygen – nonmetal Calcium – metal Carbon – nonmetal

J Deutsch Regents Question: 08/02 #11 Which formula represents an ionic compound? (1) NaCl (2) N 2 O (3) HCl (4 )H 2 O

J Deutsch Chemical bonds are formed when valence electrons are (5.2a):  transferred from one atom to another (ionic)  shared between atoms (covalent)  mobile within a metal (metallic)

J Deutsch Ionic bonds are formed when metals transfer their valence electrons to nonmetals. The oppositely charged ions attract each other to form an ionic bond. Sodium has one valence electron and chlorine has seven. Sodium want to lose 1 electron and chlorine needs to gain 1. Sodium transfers its valence electron to chlorine Forming an Na + and a Cl - ion – sodium chloride NaCl

J Deutsch Additional atoms may be necessary to insure that all the ions formed have a stable (noble gas) electron configuration. What happens when aluminum combines with oxygen to make aluminum oxide?

J Deutsch Regents Question: 06/02 #12 Which species does not have a noble gas electron configuration? (1)Na + (2) Mg 2+ (3) A r (4) S

J Deutsch Aluminum want to lose its 3 valence electrons. Oxygen needs to gain 2 electrons. The number of electrons lost by the metal must equal the number of electrons gained by the nonmetal

J Deutsch The formula of aluminum oxide is Al 2 O 3.

J Deutsch Comparing the properties compounds with ionic bonds and compounds with covalent bonds.  Properties of ionic compounds –Solids with high melting and boiling points (strong attraction between ions) –Electrolytes: Do not conduct electricity as solids but do when dissolved or molten – ions are charged particles that are free to move –No individual molecules  Properties of molecular compounds –Low melting and boiling points (weak attraction between molecules) –Nonelectrolytes: Do not conduct electricity as solids or when dissolved or molten – no charged particles (ions) to move –Solids are soft –Forms molecules

J Deutsch Ionic solids conduct electricity when dissolved or molten. Molecular solids do not. Ionic Solid dissolved in water Molecular Solid dissolved in water Solution conducts electricity Solution doesn’t conduct electricity

J Deutsch Regents Question: 01/03 #35 Which of the following solids has the highest melting point? (1) H 2 O(s) (2) Na 2 O(s) (3) SO 2 (s) (4) CO 2 (s)

J Deutsch Regents Question: 06/02 #61-63 Testing of an unknown solid shows that it has the properties listed below. (1) low melting point (2) nearly insoluble in water (3) nonconductor of electricity (4) relatively soft solid State the type of bonding that would be expected in the particles of this substance. Explain in terms of attractions between particles why the unknown solid has a low melting point. Explain why the particles of this substance are nonconductors of electricity. Covalent The attraction between particles is weak because there are no charged particle. Molecular substances are non- electrolytes – they do not form ions.

J Deutsch When nonmetals combine with nonmetals, they share electrons. The attraction of two atoms for a shared pair makes a covalent bond. Electrons are always shared in pairs. Sharing electrons fills the valence shell with 8 electrons (2 for hydrogen.) Hydrogen chloride water ammonia methane

J Deutsch Regents Question: 06/03 #12 Which type of chemical bond is formed between two atoms of bromine? (1)Metallic (2) Hydrogen (3) ionic (4) covalent

J Deutsch In a multiple covalent bond, more than one pair of electrons are shared between two atoms. (5.2e) Diatomic oxygen has a double bond O=O (2 shared pairs) because oxygen needs 2 electrons to fill its valence shell Diatomic nitrogen has a triple bond N  N (3 shared pairs) because nitrogen needs 3 electrons to fill its valence shell Carbon dioxide has two double bonds

J Deutsch Regents Question: 08/02 #17 Which molecule contains a triple covalent bond? (1) H 2 (2) N 2 (3) O 2 (4) Cl 2

J Deutsch Molecular polarity can be determined by the shape of the molecule and the distribution of charge.  Possible shapes –Linear (X 2 HX CO 2 ) –Bent(H 2 O) –Pyramidal (NH 3 ) –Tetrahedral(CH 4 CCl 4 ) A polar molecule is called a dipole. It has a positive side and a negative side – uneven charge distribution.

J Deutsch Symmetrical (nonpolar) molecules include CO 2, CH 4, and diatomic elements... Symmetrical molecules are not dipoles.

J Deutsch Asymmetrical (polar) molecules include HCl, NH 3, and H 2 O. (5.2l) The negative side of the molecule is the side that has the atom with the higher electronegativity.

J Deutsch When an atom gains one or more electrons, it becomes a negative ion and its radius increases. When an atom loses one or more electrons, it becomes a positive ion and its radius decreases. (5.2c)

J Deutsch Regents Question: 06/02 #10 Compared to the radius of a chlorine atom, the radius of a chloride ion is (1) larger because chlorine loses an electron (2) larger because chlorine gains an electron (3) smaller because chlorine loses an electron (4) smaller because chlorine gains an electron

J Deutsch Regents Question: 08/02 #23 Which electron configuration is correct for a sodium ion? (1)2–7 (2) 2–8 (3) 2–8–1 (4) 2–8–2

J Deutsch Regents Question: 01/03 #14 Given the equation: This equation represents the formation of a (1) fluoride ion, which is smaller in radius than a fluorine atom (2) fluoride ion, which is larger in radius than a fluorine atom (3) fluorine atom, which is smaller in radius than a fluoride ion (4) fluorine atom, which is larger is radius than a fluoride ion

J Deutsch When a bond is broken, energy is absorbed. When a bond is formed, energy is released. (5.2i)

J Deutsch Atoms attain a stable valence electron configuration by bonding with other atoms. Noble gases have stable valence configurations and tend not to bond. (5.2b)

J Deutsch 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. (5.2n)

J Deutsch The stronger the intermolecular forces, the higher the boiling points and melting points.  Ionic Solids  Molecules with Hydrogen bonds  Polar molecules  Nonpolar molecules Strongest Weakest For nonpolar molecules, the greater the mass, the greater the force of attraction.

J Deutsch Regents Question: 08/02 #33 The table below shows the normal boiling point of four compounds. Compound Normal Boiling Point (°C) HF (l) 19.4 CH 3 Cl (l) –24.2 CH 3 F (l) –78.6 HCl (l) –83.7 Which compound has the strongest intermolecular forces? (1) HF(l) (2) CH 3 Cl(l) (3)CH 3 F(l) (4)HCl(l)

J Deutsch Electron-dot diagrams (Lewis structures) can represent the valence electron arrangement in elements, compounds, and ions. (5.2d) atom ion molecular compound ionic compound

J Deutsch Dots represent valence electrons. Everything else (inner shell electrons and nucleus) is called the Kernel and is represented by the symbol. Phosphorous has 5 valence electrons so we draw 5 dots around the symbol for phosphorous.

J Deutsch Regents Question: 06/03 #11 What is represented by the dots in a Lewis electron- dot diagram of an atom of an element in Period 2 of the Periodic Table? (1) the number of neutrons in the atom (2) the number of protons in the atom (3) the number of valence electrons in the atom (4) the total number of electrons in the atom

J Deutsch The correct order to fill in the dots is to make a pair from the first 2 electrons then we fill in one on each side before we pair up. Ne It does not matter which side you start from.

J Deutsch The correct order to fill in the dots is to make a pair from the first 2 electrons then we fill in one on each side before we pair up. Ne This will let you know how many electron pairs and how many unpaired electrons are in the atom’s valence shell

J Deutsch Draw the Lewis Dot Structures of the first 18 elements.

J Deutsch When metals lose electrons to form ions, they lose all their valence electrons. The Lewis Dot Structure of a metal ion has no dots. The charge indicates how many electrons were lost. Magnesium atom Magnesium ion

J Deutsch When nonmetals gain electrons, they fill up their valence shell with a complete octet (except hydrogen.) The ion is placed in brackets with the charge outside the brackets.

J Deutsch A + metal ion is attracted to a – nonmetal ion (opposites attract) forming an ionic compound. We can use Lewis dot structures to represent ionic compounds. The formula for magnesium fluoride is MgF 2

J Deutsch Regents Question: 06/02 #51-53 Draw the electron-dot (Lewis) structure of an atom of calcium. Draw the electron-dot (Lewis) structure of an atom of chlorine. Draw the electron-dot (Lewis) structure of calcium chloride.

J Deutsch Regents Question: 08/02 #53 Draw an electron-dot diagram for each of the following substances: A calcium oxide (an ionic compound) B hydrogen bromide C carbon dioxide

J Deutsch Electronegativity indicates how strongly an atom of an element attracts electrons in a chemical bond.

J Deutsch Electronegativity values are assigned according to arbitrary scales. (5.2j) Fluorine is assigned the value 4.0 – the highest of any element Nonmetals have high electronegativity – they want to attract electrons so they can fill their valence shell Metals have low electronegativity – they want to lose electrons to get rid of their valence shell

J Deutsch Regents Question: 01/03 #10 The strength of an atom’s attraction for the electrons in a chemical bond is the atom’s (1) electronegativity (2) ionization energy (3) heat of reaction (4) heat of formation

J Deutsch The electronegativity difference between two bonded atoms is used to assess the degree of polarity in the bond. (5.2k)  Polar covalent bonds form between two different nonmetals  Polar bonds have a negative side and a positive side  The electrons are attracted more to the atom with the higher electronegativity.  The atom with the higher electronegativity is the negative side of the bond.

J Deutsch Regents Question: 06/03 #13 Which of these formulas contains the most polar bond? (1) H–Br (2) H–Cl (3) H–F (4) H–I

J Deutsch Polar bonds– unequal sharing- occur between two different nonmetals Nonpolar bonds– equal sharing- occur between two of the same nonmetals Ionic bonds– transfer of electrons- occur between a metal and a nonmetal Three types of bonds

J Deutsch 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. (5.2h)

J Deutsch Polyatomic ions are groups of atoms covalently bonded together that have a negative or positive charge.

J Deutsch Polyatomic ions are held together by covalent bonds but form ionic bonds with other ions. H N H Cl H H + - Covalent bonds Ionic bond

J Deutsch The bonds holding metals together in their crystal lattice are called metallic bonds.  All metals have metallic bonds  “Positive ions immersed in a sea of mobile electrons” –Bonds are between Kernels, leaving the valence electrons free to move from atom to atom –Mobile electrons give metals the ability to conduct electricity

J Deutsch Regents Question: 06/02 #8 Metallic bonding occurs between atoms of (1) sulfur (2) copper (3) Fluorine (4) carbon

J Deutsch Regents Question: 01/03 #15 The high electrical conductivity of metals is primarily due to (1) high ionization energies (2) filled energy levels (3) mobile electrons (4) high electronegativities

J Deutsch Regents Question: 06/03 #33 Which substance contains metallic bonds? (1) Hg(l) (2) H 2 O(l) (3) NaCl(s) (4)C 6 H 12 O 6 (s)

J Deutsch Regents Question: 01/03 #39 A chemist performs the same tests on two homogeneous white crystalline solids, A and B. The results are shown in the table below. The results of these tests suggest that (1) both solids contain only ionic bonds (2) both solids contain only covalent bonds (3) solid A contains only covalent bonds and solid B contains only ionic bonds (4) solid A contains only ionic bonds and solid B contains only covalent bonds

J Deutsch Regents Question: 01/03 #57-60 Each molecule listed below is formed by sharing electrons between atoms when the atoms within the molecule are bonded together. Molecule A: Cl 2 Molecule B: CCl 4 Molecule C: NH 3 Draw the electron-dot (Lewis) structure for the NH 3 molecule. Explain why CCl 4 is classified as a nonpolar molecule. Explain why NH 3 has stronger intermolecular forces of attraction than Cl 2. Explain how the bonding in KCl is different from the bonding in molecules A, B, and C. It is symmetrical. There is an even charge distribution around the molecule. Ammonia has hydrogen bonds, chlorine is nonpolar. KCl is ionic and molecules A, B and C are molecular with covalent bonds.