Chapter 9 Chemical Bonding

Objectives

• 9.1 Predict the type of bond that forms between atoms by using their electronegativity values

• 9.1 Compare and contrast characteristics of ionic, covalent, and polar compounds

• 9.1 Interpret the sea of electrons model of metallic bonding

Electronegativity

• The measure of the ability of an atom in a bond to attract electrons– How bad do they want electrons

• Each atom has their own value. • The difference in desire results in different

levels of sharing of electrons• Metals = Small• Non-metals = Large

Electronegativity

– High is 4.0 (Flourine), Low is 0.7 (Francium)• Large difference means Ionic bond• Small difference means Polar Covalent bond• No difference means Non-Polar covalent bond• Book suggests numbers, but we will continue

to summarize it as Metal + Non-metal = Ionic, Non-metal + non-metal = Polar covalent (unless same)

Ionic Bonds•What is an Ionic Bond?

- An Ionic Bond is a chemical bond resulting from the TRANSFER of electrons from one bonding atom to another

• When is an ionic bond formed?- An ionic bond is formed when a cation (positive ion/metal) transfers electrons to an anion (negative ion/non-metal).

What are some characteristics of an ionic bond?

1. Crystalline at room temperatures

2. Have higher melting points and boiling points compared to covalent compounds

3. Conduct electrical current in molten or solution state but not in the solid state

4. Very Polar Bonds

Covalent Bonds•What is a Covalent Bond?

- A covalent bond is a chemical bond resulting from SHARING of electrons between 2 bonding atoms.

• What forms a covalent bond?-A covalent bond is formed between two nonmetals.-If same atom = non-polar, if diff = polar

What are some characteristics of a covalent bond?

1. Covalent bonds have definite and predicable shapes.

2. Very strong INTRAforces

3. Low melting and boiling points

Covalent Bonds can have multiple bonds, so you should be familiar with the following…

Single Covalent Bond- chemical bond resulting from sharing of an electron pair between two atoms.

Double Covalent Bond- chemical bond resulting from sharing of two electron pairs between two atoms.

Triple Covalent Bond-chemical bond resulting from sharing of three electron pairs between two atoms.

More on Polar-Covalent

• When sharing is unequal, you end up with a slightly positive and slightly negative atom. – If Carbon and Oxygen form a bond, since Oxygen is

more electronegative, it will have a slight negative charge

• Polar bonds lead to polar molecules, where a molecule can have positive and negative sides.

• The more polar it is, the larger the boiling point/melting point

Polar Covalent

• Oxygen and Hydrogen form a polar-covalent bond. This results in water being polar. Water has a high melting point for its size, due to its polarity.

• Polar bonds also results in Acids when talking about hydrogen. HCl is a polar-covalent bond. Since the sharing is very unequal, the hydrogen falls off (no electron to share) (More later on acids in a future chapter )

• A polar bond forms when two atoms of between two atoms involved in a bond have significantly different electronegativities. – Most electronegative substance will have a slight

negative charge (represented as )– The positive (electron poor) side of the bond is

represented as + or

Metallic BondingWhat is a Metallic Bond?- A metallic bond occurs in metals. A metal consists of positive ions surrounded by a “sea” of mobile electrons.

Name 4 Characteristics of a Metallic Bond.

1. Good conductors of heat and electricity

2. Great strength

3. Malleable and Ductile

4. Luster

This shows what a metallic bond might look like.

Predict the Bond

• N and N• O and N• Cl and K• Fe and O

• Rank the following bonds by polarity (smallest to largest)

• F and S• F and O• F and Na• F and F• Which of the above has

the negative charge?

9.2 Objectives

• 9.2 Diagram electron dot structures for molecules

• 9.2 Formulate three dimensional geometry of molecules from electron dot structures

• 9.2 Predict molecular polarity from three dimensional geometry and bond polarity

Review

• Valence electrons: Hydrogen = 1, Carbon = 4, Nitrogen = 5, Oxygen = 6, Flourine = 7

• Lewis dot diagram: Places valence electrons around atom in up to 4 shells (1 s and 3 p’s)

• Your goal will be to arrange electrons so that all atoms have 8 valence and then predict the shape

Forming a molecule

• Carbon makes the best center molecule. If you don’t have a carbon, the closer you are to Carbon’s column, the better. Hydrogen and Halogens are the end of a chain.

• Arrange the atoms by connecting electrons that are all by themselves to other atoms electrons who are also not paired up

Examples

• 2 Hydrogens and 1 Oxygen• 3 Hydrogens and 1 Nitrogen• 1 Carbon, 2 Hydrogens, and 1 Oxygen

Shape

• Atoms and electrons pairs (from now on called Lone Pairs) will spread themselves out as far as possible from one another. – Lone Pairs take up more space than an actual

bond, which leads to bending of the bond angles• Double and Triple bonds count as 1 electron

cloud/pair

Effect of the number of electron pairs around the central atom

2 charge clouds, linear

3 charge clouds, trigonal planar

4 charge clouds, tetrahedral

5 charge clouds, trigonal bipyramidal

6 charge clouds, Octahedral

Chapter 10-22

Next Slide will not be tested over

• Some atoms can form more than 4 bonds because of an expanded octet (use D orbitals to bond)

John A. SchreifelsChemistry 211 Chapter 10-24

Trigonal Planer

Tetrahedral

Linear

Octahedral

Trigonal Bipyramidal

Notice all the different types of shapes that the atoms can take on because of their bonding…

Is the molecule Polar?

• If the molecule is symmetrical from all angles, it is polar (through center)

• If the molecule has any non-symmetrical view points (through center) is will be polar to some extent

• What is the shape and polarity of the following molecule? Water, Ammonia, and Carbon Dioxide?

Properties Revisited

• Non-polar molecules tend to have very low boiling points (such as carbon dioxide)

• Polar molecules tend to be somewhere between non-polar and ionic (such as water)

• Ionic compounds have very high boiling points and melting points (such as salt)

Solubility

• The rule is “likes dissolve likes”• Polar molecules tend to dissolve other polar

molecules • Non-polar molecules tend to dissolve other

non-polar molecules– Water dissolves sugar (which are polar)– Soap dissolves greases (which are non-polar)