Unit 2: All Biology is ChemistryLesson 2: Compounds

and Chemical Bonding

Drill – October 7, 2011

Create the proper MLA citation for the following:

A student visits a website that was created on September 6, 2005 by George Jones. Mr. Jones created a web article entitled All About Carbon on the American Chemical Society website. The student accessed this site on October 11, 2010.

Drill – October 19, 2011

Read the Making Bonds article.Answer the following question:• What makes atoms bond?

Objectives

At the conclusion of this lesson students will be able to:

1. Define compound.2. Explain why elements combine to

form compounds.3. Define the term chemical bond.4. Compare and contrast ionic and

covalent bonds.5. Understand why ionic and covalent

bonds form.6. Predict which type of bond will likely

form when given two or more elements.

Compounds

Most elements do not exist alone in nature.

Atoms combine to form compounds.– Compounds are substances

containing atoms of two or more elements that are chemically combined in fixed proportions

Obj. 1 & 2

Compound:

from the Latin componere, meaning “to put together”

When Two Atoms Meet

The individual subatomic particles either attract or repel one another.

– Electron-electron repulsions

– Nucleus-nucleus repulsions

– Electron-nucleus attractions

When Two Atoms Meet

Repulsions increase the kinetic energy of particles – they are trying to get away from one another.

Attractions decrease the kinetic energy of particles – they try to come together.

Atoms prefer arrangements that minimize the kinetic energy of their particles.

Why Combine? Compounds form

because atoms prefer to have a valence energy level that is filled with electrons.

A partially-filled outermost energy level usually achieves minimization of energy among atomic particles making the atom more stable electrically.

Does this carbon atom have a filled valence energy level?

= neutron

= proton

= electronObj. 1 & 2

(This is a generalization and is not entirely true.)

Achieving ‘Stability’

Atoms can become stable by attaining at least one of the following:– They fill their valence energy

level with the maximum amount of electrons that it will hold.

OR– They fill their valence energy

level with eight electrons.• The Octet Rule

Driving Forces The Laws of Thermodynamics

When atoms come into proximity to one another, their electrons repel one another and no bond forms unless…The atoms are moving with sufficient speed (i.e. kinetic energy).

The first law of thermodynamics states that energy cannot be created nor destroyed but it can be converted from one form into another.

Bond Energy

Bonds form when the kinetic energy of colliding atoms overcomes their initial repulsion and any resulting forces of attraction are greater than any remaining forces of repulsion.

All That Energy!

This kinetic energy can…– be lost as heat or light, or– be stored in a chemical bond.

Chemical bonds are the attractions that hold two or more atoms together to form a compound.Bonds form energy is storedBonds broken energy is released

Obj. 3

Two Ways to Bond

Ionic BondsCovalent

Bonds

The Sodium-Chlorine Ionic Bond

Sodium11 p12 n

Chlorine17 p18 n

Sodium atom (atomic #: 11)

Chlorine atom (atomic #: 17)

How many electrons does each atom have now?

How does this affect the total charge of each atom?

The Sodium-Chlorine Ionic Bond

Sodium11 p12 n

Chlorine17 p18 n

These atoms are no longer electrically neutral.

Protons +11Electrons

-10Charge +1

Protons +17Electrons

-18Charge -1

These atoms are stable, but because of their opposite charges they now attract one another.

How many protons does sodium (Na) have?

How many electrons does Na have now?

What is the total charge of this atom of sodium?

The Sodium-Chlorine Ionic BondAn atom with an electrical charge is called an ion. As a result of their opposite charges, sodium ions and chlorine ions attract each other.

Sodium11 p12 n

Chlorine17 p18 n

Sodium ion +1

Chlorine ion-1

An ionic bond is the chemical bond formed between ions with opposite charges.Obj. 4 & 5

This new substance is a compound called sodium chloride.

Predicting the Tendency of Atoms to Ionic Bond

© Art Branch, Inc.

Ionic Bonds Reviewed

Ionic bonds…• involve a __________ of

electrons.• result when ______ of

___________ charges attract each other.

Back to Two Ways to Bond

Drill24 October 2011

Students should answer the following questions in their notebooks:

a. A _________ ________ is an attraction that holds two or more atoms together to form a compound.

b. Atoms can become more stable by filling their outermost energy level with ______ electrons.

c. An atom with an electrical charge is called an ____________.

d. A(n) _______ ________ is the chemical bond formed between ions with opposite charges.

There IS Another Way

What happens when an atom has 4, 5, or even 6 valence electrons?

Atoms can also share one or more pairs of electrons. – When two atoms share electrons, the

shared electrons occupy orbitals around both of the atoms.

– The electrons move so quickly that it is difficult to predict which atom they are orbiting at any given time.

Water – A Model of Covalent Bonding

Hydrogen

1 p0 n

Oxygen

8p8n

Hydrogen atom (atomic #: 1)

Oxygen atom (atomic #: 8)

How many valence electrons does each atom have?

How many more electrons does each atom need to fill its outermost energy level?

Obj. 5

Water – A Model of Covalent Bonding

Hydrogen

1 p0 n

Oxygen

8p8n

Hydrogen

1 p0 n

This is a molecule of water. It can also be referred to by its chemical formula, H2O.

A shared pair of electrons can be considered to be part of the outermost energy level of both atoms that share them.

This is a molecule of water. It can also be referred to by its chemical formula, H2O.

A shared pair of electrons can be considered to be part of the outermost energy level of both atoms that share them.

How might each of these atoms fill its outermost energy level?

Hydrogen

1 p0 n

Oxygen

8p8n

If each hydrogen atom shares a pair of blinking electrons with oxygen, how many valence electrons does each atom have?

Covalent BondA covalent bond forms when two

atoms share one or more pairs of electrons.– A molecule is the simplest part of a

substance that retains all the properties of that substance

Obj. 2

Organic CompoundsCarbon has an outermost energy level that is partially filled. Its outermost level contains only four electrons. Because of this carbon can form many covalent bonds with other atoms and create a wide variety of compounds. This is why carbon is an essential element for all life.

= neutron

= proton

= electron

Compounds that contain one or more atoms of carbon are called organic compounds.

Comparing Ionic & Covalent Bonds

Ionic bonds Covalent bonds

Electrons are transferred

Electrons are shared

Usually occur when group IA

and IIA elements bond with group VIIA elements.

Usually occur between

nonmetals (i.e. C, H, N, O)

2nd strongest type of

chemical bond

Strongest type of chemical

bond

Examine the following table:

Obj. 4

Drill

Complete the Venn Diagram.

Ionic Bonds

Covalent Bonds

Obj. 4

Guess the Bond!

Examine each set of elements below. Which sets will likely bond together using ionic bonds? Which ones will likely bond using covalent bonds?

Na & ClC & H

Mg & ClK & IN & OSi & OH & SObj. 6

Glossary – Part 1

chemical bond – an attraction that holds two or more atoms together to form a compound

covalent bond – chemical bond in which two atoms share one or more pairs of electrons

ion – an atom or molecules that has an electrical charge

ionic bond – chemical bond formed from the attractive forces between ions of opposite charges

Glossary – Part 2

kinetic energy – energy of motionmolecule – is the simplest part of a

substance that retains all the properties of that substance

organic compound – a compound that contains the element carbon

valence – refers to the outermost energy level of an atom or the electrons contained in that outermost energy level

Works Cited

"2010 January « Leirith's Journal." Web log post. Leirith's Journal. Jan. 2010. Web. 14 Oct. 2010.

Campbell, Neil A., Brad Williamson, and Robin J. Heyden. Biology: Exploring Life. Upper Saddle River, NJ: Pearson Education, 2004.

Emsley, John. The Elements. 3rd. Oxford: Clarendon Press, 1998.

Postlethwait, John H., and Janet L. Hopson. Modern Biology. Austin, TX: Holt, Rinehart and Winston, 2006.

Witz, Dan. "Mosh Pit." 1998. DFN Gallery. Web. 12 Oct 2006