Chapter 12 Lecture Conceptual Integrated Science Second Edition © 2013 Pearson Education, Inc....

Chapter 12 Lecture

ConceptualIntegrated Science

Second Edition

© 2013 Pearson Education, Inc.

Chemical Bonds and Mixtures


This lecture will help you understand:

• Electron-Dot Structures• The Formation of Ions• Ionic Bonds• Metallic Bonds• Covalent Bonds• Polar Covalent Bonds• Molecular Polarity• Molecular Attractions• Most Materials Are Mixtures• The Chemist's Classification of Matter• Solutions• Solubility


Electron-Dot Structures

• Atoms bond together through their electrons. To learn about bonding, therefore, we need to know something about how the electrons in an atom are organized.

• Electrons behave as though they are contained within seven concentric shells.



• The numbers indicate the maximum number of electrons each shell may contain.

Note:• This is a "conceptual model"

and not a representation of what an atom "looks like."

• Rather, it helps us tounderstand how theelectrons in atoms behave.



• The shells are more easily drawn in two dimensions.

• Each atom has its own configuration of electrons. Elements in the same group have similar configurations, which is why they have similar properties.



• Valence electrons are electrons in the outermost shell of an atom. These are the ones that can participate in chemical bonding.

• An electron-dot structure is a notation that shows the valence electrons surrounding the atomic symbol.


Kr


• Special Note– For heavier atoms, some valence electrons

are more available than others. Krypton, for example, has 18 valence electrons, but only eight of these are typically shown in an electron-dot structure. These are the eight that extend farthest away from the nucleus.



• Note that elements in the same group have the same electron-dot structure.


Electron-Dot StructuresCHECK YOUR NEIGHBORSodium, Na, atomic number 11, has only one valence electron. Upon losing this electron, what other atom in the periodic table does the sodium resemble?

A. neon, Ne, atomic number 10

B. magnesium, Mg, atomic number 12

C. lithium, Li, atomic number 3

D. Sodium can resemble only sodium.

Explain your answer to your neighbor.


Electron-Dot StructuresCHECK YOUR ANSWERSodium, Na, atomic number 11, has only one valence electron. Upon losing this electron, what other atom in the periodic table does the sodium resemble?

A. neon, Ne, atomic number 10

B. magnesium, Mg, atomic number 12

C. lithium, Li, atomic number 3

D. Sodium can resemble only sodium.

Explanation:

With 10 electrons, the sodium has enough electrons to fill the first and second shells, just like neon, Ne.


The Formation of Ions

• An ion is an atom that has lost or gained one or more electrons.


H O

H

H+

Water Hydrogen ion

H O

H

H+

Hydronium ion, H3O+


• A molecular ion is typically formed by the loss or gain of a hydrogen ion, H+.


Na+ F-

Ionic Bonds

• An ionic bond is the electrical force of attraction between oppositely charged ions.


Ionic BondsCHECK YOUR NEIGHBOR

What is the chemical formula for a compound made of aluminum ions, Al3+, and oxygen ions, O2–?

• AlO

• Al3O2

• Al2O3

• Al6O6



Ionic BondsCHECK YOUR ANSWER

What is the chemical formula for a compound made of aluminum ions, Al3+, and oxygen ions, O2–?

• AlO

• Al3O2

• Al2O3

• Al6O6


Ionic BondsCHECK YOUR NEIGHBORWhat is the chemical formula for a compound made of magnesium ions, Mg2+, and oxygen ions, O2–?

A. MgO

B. Mg2O2

C. Mg4O4

D. any of the above



Ionic BondsCHECK YOUR ANSWERWhat is the chemical formula for a compound made of magnesium ions, Mg2+, and oxygen ions, O2–?

A. MgO

B. Mg2O2

C. Mg4O4

D. any of the above

Explanation:

The chemical formula is used to show the ratio in which atoms combine. By convention, the lowest numbers are preferred, so 1:1 is used rather than 2:2. The numeral 1, however, is implied when no subscript is written.


Metallic Bonds

• Outer electrons in metal atoms are held only weakly by the nucleus.

• This weak attraction allows the electrons to move about quite freely.

• This mobility of electrons accounts for many metallic properties.


Metallic Bonds

• An alloy is a mixture of metallic elements.


Covalent Bonds

A covalent bond is the type of electrical attraction in which atoms are held together by their mutual attraction for shared electrons.


F — FF F

Covalent Bonds

• There are two electrons in a single covalent bond.

• The covalent bond is represented using a straight line.


Covalent Bonds

• The number of covalent bonds an atom can form equals its number of unpaired valence electrons.


Covalent Bonds


Covalent Bonds

• Multiple covalent bonds are possible.


Polar Covalent Bonds

• Electrons in a covalent bond are shared evenly when the two atoms are the same.



• Electrons in a covalent bond may be shared unevenly, however, when the bonded atoms are different.


High

Low


• Electronegativity is the ability of a bonded atom to pull on shared electrons. Greater electronegativity means greater "pulling power."


Polar Covalent BondsCHECK YOUR NEIGHBORWhich is heavier: carbon dioxide, CO2, or water, H2O?

A. Carbon dioxide is heavier.

B. Water is heavier.

C. Both have the same number of atoms, so they weigh the same.

D. It depends on other factors.



Polar Covalent BondsCHECK YOUR ANSWERWhich is heavier: carbon dioxide, CO2, or water, H2O?

A. Carbon dioxide is heavier.

B. Water is heavier.

C. Both have the same number of atoms, so they weigh the same.


Explanation:Look to the periodic table and add up the masses of the atoms in each of these substances. Carbon dioxide adds up to 44 amu, while water is only 18 amu. So, carbon dioxide is more than twice as heavy. At room temperature, carbon dioxide is a gas because it is nonpolar.


Molecular Polarity

• If the polar bonds in a molecule are facing in equal and opposite directions, the polarity may cancel out.


Molecular Polarity

…Or not!


Molecular Polarity


Molecular PolarityCHECK YOUR NEIGHBORWater has such a relatively high boiling point because water

A. is such a heavy substance.

B. is transparent so that heat passes right through it.

C. contains three atoms per molecule.

D. molecules are so sticky.



Molecular PolarityCHECK YOUR ANSWERWater has such a relatively high boiling point because water

A. is such a heavy substance.

B. is transparent so that heat passes right through it.

C. contains three atoms per molecule.

D. molecules are so sticky.

Explanation:

The slightly negative end of one water molecule holds onto the slightly positive end of another water molecule. This force of attraction must be overcome before the liquid water can transform into the gaseous phase.


Na+ Cl-

H

OH

HO

H

HO

HO

H

H

OH

H H

HO

Molecular Attractions

• An ion dipole attraction is the attraction between an ion and a dipole.– Example: NaCl in water



• An dipole-dipole attraction is the attraction between two dipoles. – Example: cohesive forces within water



• A dipole–induced dipole attraction is the attraction between a dipole and an induced dipole.


Molecular AttractionsCHECK YOUR NEIGHBOR

Is it possible for a fish to drown?

A. no, because fish breathe water

B. yes, when the water contains too little oxygen

C. no, because water is 88.8% oxygen by mass

D. yes, when the water is not moving



Molecular AttractionsCHECK YOUR ANSWER

Is it possible for a fish to drown?

A. no, because fish breathe water

B. yes, when the water contains too little oxygen

C. no, because water is 88.8% oxygen by mass

D. yes, when the water is not moving

Explanation:

Fish don't breathe water. Their gills extract the small amounts of dissolved oxygen, O2, that can be found even in water that remains still.


Molecular AttractionsCHECK YOUR NEIGHBORA nonpolar material, such as oxygen, O2, is soluble in a polar material, such as water, H2O, by way of

A. ion–dipole attractions.

B. dipole–dipole attractions.

C. dipole–induced dipole attractions.

D. all of the above



Molecular AttractionsCHECK YOUR ANSWERA nonpolar material, such as oxygen, O2, is soluble in a polar material, such as water, H2O, by way of

A. ion–dipole attractions.

B. dipole–dipole attractions.

C. dipole–induced dipole attractions.

D. all of the above

Explanation:

This is a relatively weak force of attraction, which explains why not much oxygen dissolves in the water. There is enough, however, to allow fish to live.



• A fourth molecular attraction is the induced dipole–induced dipole, which occurs between nonpolar molecules.


Nonpolar atoms are attracted to each other by these "momentary" dipoles.



The larger the atom, the stronger the "momentary" dipole.




The tiny nonpolar fluorine atoms in Teflon provide very weakattractions, which is why Teflon provides a "nonstick" surface.


So, how do the gecko's sticky feet stay so clean?



Molecular AttractionsCHECK YOUR NEIGHBORWhich type of molecular attraction takes the least amount of energy to break apart?

A. ion–dipole attractions

B. dipole–dipole attractions

C. dipole–induced dipole attractions

D. induced dipole–induced dipole attractions



Molecular AttractionsCHECK YOUR ANSWERWhich type of molecular attraction takes the least amount of energy to break apart?

A. ion–dipole attractions

B. dipole–dipole attractions

C. dipole–induced dipole attractions

D. induced dipole–induced dipole attractions

Explanation:

The induced dipole–induced dipole attraction is the weakest of the four, but only on a molecule-to-molecule basis.

Remember, each hook on a strip of Velcro may be weak, but all the tiny hooks working together can provide significant holding power.


Most Materials Are Mixtures

• A pure substance is a material that consists of only one type of element or compound.

• A mixture is a collection of two or more pure substances.

• It can be separated by physical means.


Most Materials Are Mixtures


The Chemist's Classification of Matter



• Pure materials consist of a single element or compound.

• Impure materials consist of two or more elements or compounds.

• Mixtures may be heterogeneous or homogeneous.



• In heterogeneous mixtures, the different components can be seen as individual substances.

• In homogeneous mixtures, the composition is the same throughout.



• Homogeneous mixtures:– Solution: all components in the same phase– Suspension: different components in different

phases


The Chemist's Classification of MatterCHECK YOUR NEIGHBORIs the air in your house a homogeneous or a heterogeneous mixture?

A. homogeneous, because it is mixed very well

B. heterogeneous, because of the dust particles it contains

C. homogeneous, because it is all at the same temperature

D. heterogeneous, because it consists of different types of molecules



The Chemist's Classification of MatterCHECK YOUR ANSWERIs the air in your house a homogeneous or a heterogeneous mixture?

A. homogeneous, because it is mixed very well

B. heterogeneous, because of the dust particles it contains

C. homogeneous, because it is all at the same temperature

D. heterogeneous, because it consists of different types of molecules


Solutions

• A solution is a homogenous mixture consisting of ions or molecules.

• A solvent is the major component of a solution.• A solute is the minor component of a solution.• If a solution is saturated, then no more solute will

dissolve in it.


ConcentrationAmount of solute

Amount of solution

Solutions

• Concentration is a measure of the amount of solute dissolved in solution.

• A solution with more solute than solution is called concentrated.

• A solution with more solution than solute is called dilute.

=


The formula mass of a

substance expressed in

grams contains 1 mole.

Substance Formula Mass

Carbon, C 12

Oxygen, O2 32

Carbon dioxide, CO2 44

Sucrose, C12H22O11 342

Solutions

• A mole is a super-large number, 6.02 1023, used to measure numbers of atoms or molecules, also called Avogadro's number.


Sucrose, C12H22O11

Solutions

= 342 g/mole


SolutionsCHECK YOUR NEIGHBOR

Water, H2O, has a formula mass of 18. How many moles of water are there in 18 grams of water?

A. 0.5 mole

B. 1 mole

C. 9 moles

D. 18 moles



SolutionsCHECK YOUR ANSWER

Water, H2O, has a formula mass of 18. How many moles of water are there in 18 grams of water?

A. 0.5 mole

B. 1 mole

C. 9 moles

D. 18 moles


SolutionsCHECK YOUR NEIGHBOR

How many grams of water, H2O, are there in 2 moles of water?

A. 1 gram

B. 9 grams

C. 18 grams

D. 36 grams



SolutionsCHECK YOUR ANSWER

How many grams of water, H2O, are there in 2 moles of water?

A. 1 gram

B. 9 grams

C. 18 grams

D. 36 grams


Molaritymoles of Solute

liter of Solution

Solutions

• Molarity is a unit of concentration expressed in moles of solute per liter of solution.

=


1 ppm1 part solute

1,000,000 parts solution

1 milligram solute

1 liter solution =

Solutions

• ppm is a unit of concentration expressed in milligrams of solute in per liters of solution.

=


Solubility

• Solubility is the ability of a solute to dissolve in a solvent.

• A solute that has appreciable solubility is said to be soluble.


Solubility

• A precipitate is solute that comes out of solution.


SolubilityCHECK YOUR NEIGHBORThe amount of oxygen, O2, dissolved in the waters of the Arctic Ocean is –––––––– the amount of oxygen dissolved in warm tropical waters.

A. greater than

B. about equal to

C. less than




SolubilityCHECK YOUR ANSWERThe amount of oxygen, O2, dissolved in the waters of the Arctic Ocean is –––––––– the amount of oxygen dissolved in warm tropical waters.

A. greater than

B. about equal to

C. less than


Explanation:

The solubility of oxygen in water decreases with increasing temperature. As a consequence, cold polar oceans tend to be more fertile than warmer tropical waters.


Chapter 12 ReviewCHECK YOUR NEIGHBOR

By mass, water is 88.88% oxygen. So, why can't we breathe water?

Hint: What is the elemental formula for the oxygen we breathe and the chemical formula for water?


Chapter 12 Lecture Conceptual Integrated Science Second Edition © 2013 Pearson Education, Inc....

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