Unit 7a: Molecules-lecture Regents Chemistry ’14 Mr ......Unit 7a: Molecules-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Website upload 2014 Page 8 of 43 Ionic Compounds: Ionic

Unit 7a: Molecules-lecture Regents Chemistry ’14-‘15 Mr. Murdoch

Website upload 2014 Page 1 of 43

Unit 7a:

Molecules

1.

Student Name: _______________________________________

Class Period: ________



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Unit 7a Vocabulary:

1. Binary compound: A compound that consists of only two elements.

2. Dipole attractions: The attraction of the partially negative (δ-) end of

one polar molecule to the partially positive (δ+) end of another polar

molecule.

3. Dipole moment: An arrow along the line of symmetry in a polar

molecule that shows the net direction that electrons are being pulled

towards the partially negative (δ-) end of the molecule.

4. Electronegativity difference: The difference in electronegativity

between two elements in a bond.

5. Electrical conductivity (of metals): The ability of a substance to allow

electrons to pass from atom to atom through the substance from a

source of electricity to an electrical ground.

6. Electrolyte: A solution containing dissolved ions that can conduct

electricity within the solution.

7. Empirical formula: The simplest whole-number mole ratio of

elements in a compound; used to write the formulas of ionic

compounds.

8. Formula mass: The sum of the atomic masses of an element or

compound, measured in grams per mole (g/mole). Reported to the

nearest tenth (0.1) of a g/mole.

9. Hydrogen bonds: The strong attraction of the H (δ+) end of one polar

molecule to the N, O, or F (δ-) ends of another molecule. The two

molecular ends form temporary covalent bonds.

10. InterMolecular Attractive Force (IMAF): The forces that hold

molecules together in the solid and liquid phases. These are the

forces that must be overcome to melt or boil a substance. IMAF

forces are also called “van der Waal’s forces”.

11. Ionic compound: Compounds consisting of a metal and a nonmetal

ionic bonded in a whole-number ratio.

12. London Dispersion Force: The weak attractive forced caused by

temporary dipoles in nonpolar molecules.



13. Metallic bond: A bond formed between metal atoms as they

collectively share their conducting electrons evenly between metal

kernals.

14. Molecular formula: The actual number of nonmetal atoms in a

molecule; a whole-number multiple of the empirical formula.

15. Molecule: A group of nonmetal atoms covalently bonded together to

form a distinct particle.

16. Network solid: A crystal lattice formed from covalently bonded

nonmetal atoms with no distinct molecules.

17. Nonpolar molecule: A molecule with symmetrical electron

distribution resulting in any polar bonds cancelling each other out to

yield no partially charged ends.

18. Percent composition: The formula mass of an element divided by the

formula mass of the compound containing the element and the

divisor then multiplied by 100.

19. Polar molecule: A molecule with asymmetric electron distribution

resulting in partially charged ends.

20. Polyatomic ion: An ion formed by atoms bonding together in way

that a net charge (positive or negative) is formed.

21. Ternary compound: A compound that consists of three (or more)

elements, usually containing a polyatomic ion.



Notes page:



Unit 7a Homework Assignments:

Assignment: Date: Due:



Compound: A compound is a substance formed by the chemical bonding

of atoms. The type of compound is determined by the type of bonding

involved.

Topic: Types of Compounds

Objective: How do substance properties depend on composition?



Ionic Compounds:

Ionic Compounds are formed by ionic bonding.

Ionic compounds are found in crystal form of alternating + and -

charged ions.

As a full + and full - charges are involved, ionic attractions are strong.

Ionic bonds tend to have high melting and/or boiling points; ionic

bonds tend not to evaporate.

When dissolved in water or melted, the ions separate and allow

conduction of electricity. The solution formed is called an

electrolyte.

An attraction between ions is named ionic attraction.

Melting or dissolving ionic compounds breaks the ionic bond. When

the bonds have already been broken the ionic reactions are very fast.

Topic: Ionic Compounds

Objective: How do substances form compounds swapping electrons?



Molecular Compounds:

Molecular compounds are formed by covalent bonding, either polar

or nonpolar.

Covalent bonding forms individual particles called molecules which

can attract each other to form the solid or liquid phase.

Molecules may have oppositely charged ends, which allow them to

attract one another. These are called InterMolecular Attractive

Forces (IMAF), and are weaker than ionic attractions.

Molecular compounds are more easily melted and boiled, so their

solid melting and boiling points are low compared to solid ionic

compounds. Molecular compounds also tend to evaporate more

quickly, and their solids are softer than ionic or metallic bonds.

Note that dissolving in water or melting does NOT break the covalent

bond. No ions are formed, so molecules do NOT normally conduct

electricity.

Topic: Molecular Compounds

Objective: How do substances form compounds sharing electrons?



Network Solids:

Network solids (Atomic solids) are covalently bonded solids (usually

nonpolar) that do not form separate molecules.

Network solids are one single crystal made of nonmetal atoms

connected with a continuous network of covalent bonds with no

areas of weakness that may break apart. Network solids are among

the hardest substances known, such as diamond, corundum, and

quartz.

Network solids are nonconductors of electricity and poor heat

conductors.

Watch Bozeman Science Covalent Network Solids video

https://www.youtube.com/watch?v=PU9rzTjLyb4

Topic: Network Solids

Objective: What substances are made in continually bonded crystals?





Allotropes:

Allotropes are different forms of the same element.

Different bonding arrangements between atoms result in different

structures with different chemical and physical properties.

Allotropes occur only with certain elements, in Groups 13 through 16

in the Periodic Table.

Elements that form allotropes are: B, C, N, O, Al, Si, P, S, Ga, Ge,

As, Se, In, Sn, Sb, Te, Tl, Pb, Bi, and Po.

Carbon forms the most allotropes of any element.

o Carbon may be found naturally as both diamond and graphite.

Note that these are on both ends of the Moh’s hardness scale for

minerals. Carbon may also be found in a “ball-like” structure,

known as a fullerene, as carbon-60 (C60).

Diamond Graphite C 60 Fullerene

Topic: Allotropes

Objective: What elements may be found in different forms?



Metallic Compounds:

Metallic compounds do not technically form compounds with other

metal atoms.

Metal atoms share electrons by losing them. Metals ‘swap’ valence

electrons freely.

Metal atoms have positively charged kernals located amidst many

free-moving electrons. These free-moving electrons are evenly

distributed and easily move, allowing metals to conduct electricity in

all phases.

Topic: Metallic Compounds

Objective: What special properties do metallic compounds have?



Bonding Energies:

Chemical Compounds are formed when atoms are bonded together.

Energy is absorbed when a bond is broken; energy is released when

a bond is formed.

i. Individual atoms are unstable and have higher energies.

o When atoms combine into compounds, energy is released

(exothermic), and the compound is more stable than the

original atoms.

ii. Compounds have a lower potential energy than their individual

atoms.

o Breaking a chemical bond requires energy (endothermic), and

the energy required is now a part of the more unstable atoms.

o The more bonds (electron pairs) between atoms, the more

energy per electron pair, and the shorter the bond length.

Topic: Bonding Energies

Objective: How does bonding affect the energy of compounds?



Physical Properties of Types of Compounds:

Ionic, Covalent, and Metallic Bonds - YouTube

https://www.youtube.com/watch?v=CGA8sRwqIFg

Topic: Types of Compounds

Objective: How the different compounds compare and/or contrast?





Molecular Polarity:

Molecular polarity is different than the polarity of the bonds within

the molecule.

A bond is polar if the electronegative difference (END) between

bonding atoms is 0.5 or higher. A molecule may have polar bonds

and still be a nonpolar molecule. The polarity of the molecule is

determined by the polarity and positioning of all bonds within a

molecule.

Determining the polarity of a molecule may tell you several things:

i. How high (or low) the melting and/or boiling points of the

substance;

ii. How easily the liquid phase of the substance evaporates (vapor

pressure);

iii. Whether the substance will dissolve in water or another solvent.

Molecular polarity causes intermolecular attractive forces, and is

the reason certain adhesives bind, and why some animals can climb

walls and glass. The IMAF act like Velcro; you can attach and

detach the molecules without damaging them, and some molecules

are stronger than others, just as some Velcro is stronger.

Topic: Molecular Polarity

Objective: How may you tell if a molecule is polar or nonpolar?



Notes page:



Molecular shape determines the properties of the molecule.

Topic: Molecular Shape

Objective: How will the shape determine molecular properties?



Determining Molecular Polarity:

Polar Molecules:

Polar molecules contain nonmetal atoms that share electrons

unequally when forming molecules. If the resulting molecule is

asymmetrical (unbalanced), there is a greater concentration of

electrons on one side of the molecule compared to the other side of

the molecule.

The molecule will have one side charged partially negative and the

other side charged partially positive. The oppositely charged ends of

these molecules are “poles”, making the entire molecule polar. Polar

molecules may attract each other, (δ+) end of one polar molecule to

the (δ-) of the other molecule. These are the IMAF as mentioned

earlier.

If the molecule has polar bonds in an asymmetrical arrangement, the

molecule as a whole will have a net polarity towards the more

electronegative atom in the molecule. The net direction of electron

pull towards the more electronegative atom may be diagrammed by

determining the sole axis of symmetry and drawing an arrow (dipole

moment) towards the more electronegative atom.

The diagrams on the next page show some polarity examples.

Examples of each molecule used are found at the end of your packet.


Objective: How will the shape determine molecular Polarity?



POLAR MOLECULES: A Polar Molecule has one line of symmetry. The line of

symmetry forms the Dipole Moment. Look up the electronegativity (EN) of the atoms at

either end of the line of symmetry. The more EN end will be δ- and the less EN end will

be δ+. The line of symmetry has an arrowhead placed on the more EN end, forming the

Dipole Moment, or the direction (moment) in which the electrons are pulled towards.

Polar molecules have asymmetric electron distributions.

Draw an arrowhead on the

end of the line with the

highest EN. This is the

Dipole Moment. The end

with the higher EN has a

greater pull on the electrons,

so it is δ- charged. The other

end is δ+ charged, forming a

complete polar molecule.

Structural

Formula

Lines of symmetry:

either side of the line

is a mirror image.

Write the EN of the

atoms on either end of

the line of symmetry.



Nonpolar Molecules:

If the molecule has a symmetrical shape, then the electrons are

distributed evenly throughout the molecule, and the entire molecule is

nonpolar, even IF it contains polar bonds.

Nonpolar molecules have equal pull of electrons on all sides of the

molecule, so no dipole moment forms. Since the molecule lacks

oppositely charged ends, and attractive forces will be extremely

weak.

Small nonpolar molecules are usually found in the gaseous state at

room temperature, with examples including methane (CH4), propane

(C3H8), and butane (C4H10). Larger nonpolar molecules may be

liquids at room temperature, with examples including octane (C8H18)

and benzene (C6H6). Large nonpolar molecules are normally in the

solid phase at room temperature, such as p-dichlorobenzene

(C6H4Cl2), which is what mothballs are made of.


Objective: How will the shape determine molecular Polarity?





NONPOLAR MOLECULES:

Nonpolar molecules have two or more lines of symmetry. The

electronegativity differences along these lines of symmetry are equal,

so there is an equal pull on electrons from all sides of the molecule.

The molecule has a symmetrical electron distribution.

Watch Crash Course Science Polar and Nonpolar molecules video (Have seen already; a repeat!)

https://www.youtube.com/watch?v=PVL24HAesnc





London Dispersion Force:

London Dispersion Force attractions are formed in nonpolar

molecules. As there are no permanently charged positive or negative

ends, these attractions are very weak. The attractions are a

combination of temporary poles due to electron movement around

the molecule in smaller molecules.

London dispersion forces generally get stronger as the size of the

molecule increases.

Watch Bozeman Science London Dispersion Force video

https://www.youtube.com/watch?v=1iYKajMsYPY

Topic: London Dispersion Force

Objective: What attraction holds nonpolar molecules together?





Dipole Attraction:

Dipole Attractions are formed in polar molecules.

Dipole attractions are simply the attraction of the oppositely charged

ends of two molecules. The partially positive end of one molecule

attracts toward the partially negative end of another molecule. This

attraction allows these substances to exist as solids and liquids at

higher temperatures than are possible for nonpolar molecules of

equivalent size.

Topic: Dipole Attraction

Objective: What attraction holds polar molecules together?



Hydrogen Bonds:

Hydrogen Bonds are formed in some polar molecules.

Water is one of the most notable molecules with this special type of

attractive force. In water, the hydrogen atom from the partially

positive end of one water molecule is attracted to the oxygen atom

from the partially negative end of another water molecule. There is

still an electronegative attraction, as the END between H and O is 1.3

and therefore strongly polar. There are more attractive forces

occurring with these temporary covalent hydrogen bonds between one

water molecule’s oxygen and one of the hydrogen atoms in another

molecule of water. The oxygen is so electronegative (and is of such

small radius) that the oxygen atom moves the electron it shares with

its own hydrogen, and the now the hydrogen is ‘free’ to bond with

oxygen in another water molecule.

Note that the primary bond between a water molecule’s oxygen and

its own hydrogen atoms is MUCH stronger than the hydrogen bond

between different molecules oxygen and hydrogen atoms. Still the

hydrogen bonding between water molecules is responsible for the

amazing properties of water.

Topic: Hydrogen Bonds

Objective: What attraction holds polar molecules (water) together?



Water Properties due to Hydrogen Bonding:

i. Water has an extremely high melting point, boiling point, heat of

fusion, and heat of vaporization for a molecule of that size;

ii. Water has the ability to form a ‘skin’ at the surface known as surface

tension that forms a meniscus and allows small animals to walk on

water;

iii. Water has the ability to climb narrow spaces, known as “capillary

action”, due to the adhesion between the wall spaces and water

molecules;

iv. Water molecules may be deflected by an electronic field.

Hydrogen atoms may form hydrogen bonds with other nonmetal

atoms with a high electronegativity and a small atomic radius, such

as nitrogen (EN of 3.0) and fluorine (EN of 4.0).

Chlorine (EN of 3.2) does NOT form hydrogen bonds, as chlorine

has a third PEL and its size interferes with the temporary covalent

hydrogen bond forming.

Watch Bozeman Science Dipole and Hydrogen Bonds video

https://www.youtube.com/watch?v=cERb1d6J4-M





Topic: Hydrogen Bonds

Objective: What attraction holds polar molecules (water) together?



Attractive Force: Type, Strength, and resulting Molecular Properties.

Lines of Symmetry

Molecule Polarity

Type of Attractive Force Strength of Attractive

Force

Melting & Boiling points

Vapor Pressure

(Evaporation potential)

0 or 1 Polar

(If H end of one molecule is attracted to a N, O, or F end of

another molecule) = HYDROGEN BOND

Strong High Low

0 or 1 Polar (Any OTHER polar molecule) =

DIPOLE Moderate Moderate Fair

2 or more Nonpolar LONDON DISPERSION

FORCE Weak Low High

What can you do with this information?

Using the flowchart on page 26, you should be able to:

i. Identify whether a compound is molecular, ionic, or a network solid

based on its properties;

ii. Draw dot diagrams of simple molecules;

iii. Draw structural formulas of simple molecules;

iv. Determine the shape of simple molecules;

v. Determine if simple molecules are polar or nonpolar;

vi. Draw the dipole movement and identify the partially charged ends of

polar molecules;

vii. Determine the type of attractive force between simple molecules.

Topic: Molecular Attractive Forces

Objective: How do different molecular attractive forces compare?



Attractive Force Summary: Flowchart



Notes page:



Student name: _________________________ Class Period: _______

Please carefully remove this page from your packet to hand in.

Types of Compounds homework

Circle the correct answer in each multiple choice question below.

1. Which of the following substances is molecular?

a) NaCl b) CO2 c) K2O d) C

2. Explain why one of the wrong choices is not molecular. Choice: ____

Why?

3. Which of the following substances has a very high melting point and will

conduct electricity when in the liquid phase?

a) NaCl b) CO2 c) CH4 d) SiO2

4. Explain why one of the wrong choices is not correct. Choice: ____

Why?

For each of the molecules represented by the structural formulas on the next page

indicate:

i. If the molecule is polar or nonpolar;

If you find the molecule is nonpolar, skip to step iii.

ii. If the molecule is polar, draw the dipole moment and mark which end is

partially positive and which side is partially negative;

iii. Identify the shape of the molecule;

iv. Identify the type of attractive force that will hold molecules of this substance

together in the liquid and solid phase.

Cont’d next page



Molecule Diagram

(Draw dipole in this

space)

Polar or

Nonpolar Shape IMAF Type Dot Diagram



Notes page:



H ̶ Cl





H ̶ O

ǀ

H





H ̶ N ̶ H

ǀ

H





H ̶ S

ǀ

H





Cl ̶ C ̶ Cl

ǀ

H

Cl

ǀ



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Unit 7a: Molecules-lecture Regents Chemistry ’14 Mr ......Unit 7a: Molecules-lecture Regents Chemistry ’14-‘15 Mr. Murdoch Website upload 2014 Page 8 of 43 Ionic Compounds: Ionic