BondingChapter 7

(Page 196)

Essential question:

Why is chemical bonding important and how can chemist predict what types of bonds will occur in a chemical reaction?

Vocabulary: Section 1 • Bonding• Polarization• Electronegetivity• Ionization energy• Nonpolar covalent bond• Ionic bond• Metallic bond• Polarize• Electrostatic force

• Compounds, not elements, determines most of what we experience in this world

• How elements bond together in compounds determines the properties of matter that we observe

• Many of the elements that we observe in nature are poisonous in their natural form, but as compounds, they sustain and enable life

• Ionic compounds, unlike covalent compounds, dissociates in water to form positive and negative ions

• Covalent compounds remain as whole units when dissolved in water

• Metals form special bonds that are neither ionic or covalent, but somewhere in the middle

• Metals conduct electricity because their valence electrons are not fixed and can move from atom to atom

• Sulfur can help life because it is an essential nutrient and is found in amino acids

• Sulfur also causes the foul smell in garlic, rotten eggs and in skunks

• Iron is important to many body functions including the transferring of oxygen from lungs to the cells (hemoglobin)

• Iron is also magnetic in nature and when the two (iron and sulfur) are mixed they each maintain their physical and chemical properties, until both are heated close to the melting point of steel (where a chemical reaction occurs)

• The resulting compound is iron sulfide and no longer has the properties of iron or sulfur, but new properties

What is a chemical bond?• Using a molecule building kit, a chemical bond is a stick and atoms

joined together• The sticks between the atoms represent bonds between each atom• Inside the atom are positive and negative charges that attract and

repel each other (protons repel other protons and electrons repel each other)

• There are also intermolecular forces, forces between one atom and another atom or atoms

• Because of protons of one atom attracting electrons of another atom, there is an array of charges that each atom has to deal with which can cause a shift in atomic charges

• Polarization is an uneven distribution of positive or negative charge that occurs when anything (like other atoms) creates an charge outside of the atom (this is how bonds form)

The electron cloud responds to changes in the electromagnetic environment.

That distortion is called polarization.

Each nucleus attracts the electron cloud of the other atom.

Each nucleus repels the other nucleus.

The electron cloud repels the other electron cloud.

At a certain distance there is an equilibrium between attractive and repulsive forces.

What happens when two hydrogen atoms approach each other?

• In nonpolar covalent bonds, the difference between the electronegativity of both atoms is very little (between 0.3 and 0.0)

• In polar covalent bonds the difference between the electronegativity of both atoms is a moderate difference (between 1.7 and 0.3)

• In ionic bonds the difference between the electronegativity of both atoms is a large difference (between 3.3 and 1.7)

• Covalent bond is formed when atoms share electrons (sometimes the sharing is equal, sometimes it is not equal sharing)

• Ionic bonds are formed when metals give 1, 2, or three electrons to a nonmetal (each atom becomes charged (as positive or negative)

• In a non-polar covalent bond, the sharing of electrons is equal so the electrons are evenly distributed so there is little charge separation on the surface of the molecule

• In a polar covalent bond, the uneven sharing of electrons creates a region that is more positive, and another area that is more positive than the opposite end.

• Metallic bonds both atoms have a low electronegativity and low ionization energy so they don’t attract each other’s electrons very well

• As a result of metallic bonding, a bunch of atoms share electrons

Assignment

• Take a new sheet of paper and fold it into three sections

• Write your name, the title of the chapter and the number

• On the first section from the sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

• Sometimes when two or more molecules combine the result can be a polar or non polar molecule, even though individual bonds are polar

• The reason for this is because when a molecule is called polar, the overall molecule is polar and not just certain bonds (the surface of the molecule can be non polar, even though is has polar bonds)

• When a chemical bond is formed, some valence electrons are either shared or transferred between atoms

• Only unpaired unshared electrons can participate in chemical bonds

• It is important to know that in the outer shell, the 5th, 6th and 7th valence electrons pair up and reduce the amount of electrons available to take part in chemical bonding

• The number of valence electrons affects bond number and ion charge

• In a molecular compound, each unpaired unshared valence electron can form one covalent chemical bond

• Example: both nitrogen and phosphorous atoms have three unpaired valence electrons (so they can form three covalent bonds)

• All atoms react chemically to reach the octet configuration

• Atoms are neutral charge but unpaired unshared electrons can cause atoms to become positive or negative ions by the gaining or loss of electrons

• When an atom (metal) loses one or more electrons, it becomes a positive ion with a “+” 1, 2, or 3 charge

• Group 1 metals lose 1 electron to become a +1 ion• Group 2 metals lose 2 electron to become a +2 ion• Group 13 metals lose 3 electron to become a +3 ion• When an atom (nonmetal) gains one or more

electrons, it becomes a negative ion with a “-” 1, 2, or 3 charge

• Group 17 metals gain 1 electron to become a -1 ion• Group 16 metals gain 2 electron to become a -2 ion• Group 15 metals gain 3 electron to become a -3 ion

Electrons are shared between the two nuclei.

A covalent bond An ionic bond

One or more electrons are transferred to form ions.

The positive and negative ions attract each other.

Some atoms are more greedy for electrons than others!

Electrons are unevenly shared between oxygen and hydrogen.

Electronegativity(electron sharing)

Oxygen is slightly more electronegative than hydrogen.This results in uneven sharing of electrons.

Atom 1

Atom 2

Difference in EN

Electron sharing

high EN

high EN

very little

equal or nearly equal sharing

high EN

medium EN

moderate

uneven sharing

high EN

low EN

large

transfer of electrons

Nonpolar covalent bond

Polar covalent bond Ionic bond

Types of bond

EN = electronegativity

Types of bond

Types of bond

Ionic bonds connect atoms to all neighbors, not just a single neighbor as in a molecule.

An ionic crystal

Types of bond

A metallic bond

Like a covalent bond

Like an ionic bond

Electrons are shared

No two atoms are specifically bonded together

metallic bond: an attraction between metal atoms that loosely involve many electrons.

Difference in EN

Electron sharing

very little

equal or nearly equal sharing

moderate

uneven sharing

large

transfer of electrons

Nonpolar covalent bond

Polar covalent bond Ionic bond

EN = electronegativity

Electronegativity of atoms: I = 2.66 I = 2.66

Difference in electronegativity: I – I = 2.66 – 2.66 = 0

Electronegativity of atoms: I = 2.66 I = 2.66

Difference in electronegativity: I – I = 2.66 – 2.66 = 0

The I–I bond is nonpolar covalent.

Electronegativity of atoms: C = 2.55 O = 3.44

Difference in electronegativity: O – C = 3.44 – 2.55 = 0.89

The C–O bond is polar covalent.

0.89

Nonpolar bonds in a molecule make the molecule nonpolar.

Polar bonds in a molecule make the molecule polar.

Assignment

• Write a three dollar summary of what you learned (a paragraph, with a topic sentence and three supporting sentences)

• Turn to page 224 and complete # 1 – 5 then turn them in

• Honors chemistry Homework:– Page 224 # 15 - 20

Vocabulary: Section 2

• Octet rule• Free radical• Antioxident• Non-polar covalent• Ionic bond• Polar covalent bond

Ionic bonds

Electron configuration of ions

Ionic bonds

Same configuration as neon (a noble gas)

Electron configuration of ions

Ionic bonds

Ionic bonds

Write the electron configuration for a magnesium ion (Mg2+).

Asked: Electron configuration of Mg2+

Given: Mg, atomic number of 12, charge of +2

Relationships: The electron configuration of magnesium is 1s22s22p63s2.

Ionic formulas

What is the correct formula for calcium oxide, a compound used in making paper and pottery, and adjusting the pH of soils?

Asked: The formula for the ionic compound calcium oxide

Given: Calcium oxide is made from calcium and oxygen ions. Calcium forms +2 ions and oxygen forms –2 ions.

Relationships: Ca2+ and O2– must combine in a ratio that will balance out the positive and negative charges.

• As stated earlier, elements share, lose or gain electrons to satisfy the octet rule and become more stable

• The exception to the octet rule are those closest to helium such a hydrogen, lithium, beryllium and boron (since helium is the closest completely stable noble gas

• For those elements mentioned above, the octet rule is more the duel rule or the rule of “2” these elements bond chemically to have a configuration of two electrons

• In a covalent bond, each shared electron is seen as a valence electron by both elements

• In H2, each atom shares a electron to have two electrons in their outer shell

• In water H2O, each the hydrogen shares an electron with the oxygen giving them two valence electrons and oxygen eight valence electrons

• When ions are formed, they have an electron configuration of the closest noble gas– Na+ has the neon configuration– O2- has the Neon configuration

Covalent bonds

Covalent bonds

Bonds form in such a way that each atom in the

compound achieves the same number of valence

electrons as the closest noble gas atom.

octet rule: rule that states that elements transfer or share electrons in chemical bonds to reach a stable configuration of eight valence electrons.

Covalent bondsElectrons are transferred so that each element has 8 valence

electrons and has the same configuration as the closest noble gas.

The light elements H, Li, Be, and B prefer to have 2 valence electrons.

Ion formationAtoms gain or lose one or more electrons to reach the same electron

configuration as the closest noble gas, with 8 valence electrons.

Assignment

• On the second section of that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

• Ionic compounds generally form crystals because of the interchanging of +tive and –tive charges

• Ionic compounds are neutral even though they are made up of trillions of charged ions

• The formula of an ionic compound can be determined as long as you cancel the positive and negative

• As stated earlier, covalent bonds share electrons not transfer them

• The number of covalent bonds is equal to the number of unpaired valence electrons

• Only hydrogen and nonmetals are commonly found as covalent bonds

• Carbon-like compounds form four covalent bond• Nitrogen-like compounds form three covalent bond• Oxygen-like compounds form two covalent bond• Halogens form one covalent bond

• Carbon has four valence electrons and they are all unpaired• Oxygen has six valence electrons, but only two are unpaired

and able to form covalent bonds• If Lewis dot structures are drawn for elements, it can be used

to tell the valence electrons and the unpaired electrons (which is the same as the number of possible covalent bonds)

• Atoms or molecules with unpaired electrons are highly reactive and are known as free radicals

• Free radicals are responsible for aging, and diseases such as cancer

• Antioxidants are a good part of diet because they prevent free radicals form reacting with and damaging DNA

Assignment• Write a detailed three dollar summary of what

you learned (a paragraph, with a topic sentence and three supporting sentences)

• Turn to page 224 and complete # 6 – 7, • Page 226 # 43 - 48 then turn them in

• Honors chemistry homework– Page 225 # 21 - 29

Vocabulary: Section 3• Isomer• Free radical• Antioxidant• VSEPR• Region of electron density• Trigonal planar• Lone pairs• Tetrahedral• Trigonal pyramidal• Bent

Each water molecule contains one oxygen atom and two hydrogen atoms.

One central oxygen atom

One hydrogen atom on either side

Why can’t a water molecule be like this?

Why can’t a water molecule be like this?

The oxygen forms one bond

One hydrogen forms two bonds

One hydrogen forms one bond

The Lewis structures indicate that it is not possible

Lewis structures for individual atoms are like puzzle pieces.Put them together to form molecules.

Use Lewis structures to predict:

1) the chemical formula

2) the bonding pattern

3) the shape of the molecule

H2O is flat and bent

To be discussed later in this section

Lewis Dot Structures• Lewis dot structures allows chemist to be able

to identify and predict how elements will join together to form molecules

• If you have a formula, you can use Lewis structures to determine how they will join

• The goal of using Lewis structures is to end up with each atom having no unpaired electrons and each having eight valence electrons (unless it is hydrogen, helium, lithium, beryllium or boron)

Use Lewis structures to predict:

1) the chemical formula

The chemical formula for water is H2O

(2 hydrogen atoms for every 1 oxygen atom)

Isomers

• Sometimes there is more than one way to satisfy the molecular formula

• Isomers are when there is more than one way to represent a chemical formula

• For example, C2H6O can form ethanol as well as dimethyl ether (they both have different chemical and physical properties)

Ethanol

Consider the chemical formula C2H6O

Consider the chemical formula C2H6O

Dimethyl ether

isomer: a specific structure of a molecule, only used when a chemical formula could represent more than one molecule.

Dimethyl etherEthanol

Two isomers of C2H6O

Give three isomers for the formula C3H8O. Show the Lewis dot diagram and the structural formula for each molecule.

Give three isomers for the formula C3H8O. Show the Lewis dot diagram and the structural formula for each molecule.

Asked: The Lewis dot diagrams and structural formulas for the three molecules represented by the formula C3H8O

Given: Carbon has four unpaired electrons, hydrogen has one, and oxygen has two. Three carbons, eight hydrogens and one oxygen form each molecule.

Relationships: The atoms will bond together such that all unpaired electrons will be paired up with electrons from other atoms.

Give three isomers for the formula C3H8O. Show the Lewis dot diagram and the structural formula for each molecule.

Asked: The Lewis dot diagrams and structural formulas for the three molecules represented by the formula C3H8O

Given: Carbon has four unpaired electrons, hydrogen has one, and oxygen has two. Three carbons, eight hydrogens and one oxygen form each molecule.

Relationships: The atoms will bond together such that all unpaired electrons will be paired up with electrons from other atoms.

Double and Triple Bonds• There are many compounds or molecules with more than one bond

between two atoms• Ethene and ethyne have double and triple bonds respectively• Oxygen also has double bonds• Lewis dot structures show two dimensional representations of

chemical bonding whit is a limitation since the 3D shape of a molecule determines the chemical properties of a molecule

• VSEPR – Valence Shell Electron Pair Repulsion• The first three words “VSE” represent the valence electrons and

how they react and the last two words “PR” represents the paired electrons that are not shared

• Paired electrons are not shared in a chemical bond, but they do effect the shape of the molecule

• Paired electrons repel each other as well as repel shared ones

Ethene Ethyne

Multiple bonds

Carbon, nitrogen and oxygen commonly form double and triple bonds.

Double bond (2 pairs of electrons)

Sharing a pair of electrons is called a single bond.

Triple bond (3 pairs of electrons)

Assignment

• On the third section of that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

Electron Density• If you rubbed a balloon against your hair, it would pull electrons

off of your hair and become more negative• If you put two charged balloons together, they would repel each

other (since similar charges repel)• The same thing happens when there are two regions of electron

density around the atom• The electrons repel each other until they are the maximum

distance apart • When you have two balloons that are negatively charged, they

move apart in a linear shape apart (180o)• When they are three areas, the shape of the repulsion (120o)

which is called trigonal planar shaped• When they are four areas, the shape of the repulsion (109.5o)

which is called tetrahedral shaped

VSEPR theory

• Molecular polarity is an uneven distribution of molecular charges between atoms

• VSEPR stands for valence-shell, electron-pair repulsion

• VSEPR theory states that repulsion between the sets of valence electrons surrounding an atom causes these sets

Two areas of electron density repel to form linear shapes

The two 180o angles formed around each carbon make the entire molecule straight.

Two regions

Three areas of electron density repel to form trigonal planar shapes

Three regions

These three regions of electron density repel, forming 120o angles between the three atoms bonded to each carbon atom

Four regions

The four regions of electron density around

the carbon repel, forming angles of 109.5o.

Four regions

Different geometries formed by atoms with four regions of electron density

Trigonal pyramidal

Tetrahedral

Bent

Water and ammonia have similar angles even though they are not the same.

Assignment

• Write a detailed three dollar summary of what you learned (a paragraph, with a topic sentence and three supporting sentences)

• Turn to page 224 and complete # 8 – 14 then turn them in

• Honors chemistry homework– Page 225 # 30 - 39

Test: - Next week Tuesday or Thursday depending on your class.

• Homework requirement: Learn all terms and concepts covered on this topic.

• Make sure you have all assignments between page 224 and 227 completed and turned in by your test date.