Chemical Bonding

Chemical BondingChapter 13

Material on Midterm

How do 100 elements make up everything in the world?

Different types of bonds create differences in the properties of substances

From Glue to Goop

Objectives:◦Describe what chemical bonds are

◦Identify how many valence electrons are in any atom

◦Explain how you know if an atom is likely to form bonds

Section 1: Electrons and Chemical Bonding

Combining Atoms through Chemical Bonding◦Most atoms hate being alone…so they

bond!

Chemical bonding is the combining of atoms to form molecules or ionic compounds

Properties of new substance are different that the properties of the old substance

The chemical bond is the interaction that holds the two atoms together.


6 + 6 + 12 =

C6H12O6

akaglucose

Combining Atoms Through Chemical Bonding◦It’s all about the electrons

◦When bonds form, electrons can… …be shared …be gained …be lost


Electron Number and Organization◦We need to organize the electrons so we

know what they will do if bonds are formed

Review: How do I know how many electrons at atom has?◦Same as its atomic number (proton #)


What are the rules for where the electrons go?


What are the rules for where electrons can go?◦Electrons do NOT like each

other! Will try to move FAR away from other electrons

ONLY pair up after 4 are on 2nd level◦N,S,E,W


Outer-Level Electrons and Bonding◦Only the valence electrons are involved

in forming chemical bonds The valence electrons are the

electrons found in the outermost shell of an atom


Valence Electrons and the Periodic Table◦Elements in the same group have the

same number of valence electrons (generally)

◦If Lithium has 1…then Sodium, Potassium, rubidium, Cesium, and Francium all have…1!


To Bond or Not to Bond◦Not all atoms bond the

same Group 18 have their

outmost shell filled.

WANNA GET TO 8! Group 18 already has 8

(except He), so they’re happy and DO NOT REACT


To Bond or Not to Bond◦ Filling the Outermost Level

Less than 8? More likely to react. Will share, take, or lose electron(s) to get to the magic

number What about 2?

Some elements that are small (H, He, Li, Be), will try to get to 2 electrons for that first shell

Will share, take, or lose electron(s) to get to this number


Section Review

1. Describe what chemical bonds are

2. Identify how many valence electrons are in any atom

3. Explain how you know if an atom is likely to form bonds


Objectives:◦Explain how ionic bonds form◦Describe how positive and negative ions form

◦Explain why ionic compounds are neutral

Section 2: Ionic Bonds


All you need to know

about ionic bonding

is right here

Forming Ionic Bonds◦An ionic bond is a bond that forms when

electrons are transferred from one atom to another atom

◦This creates ions, which are charged particles that form when atoms gain or lose electrons

As a result of an ionic bond, either positive or negative ions can form


Forming Positive ions◦Positive ions form when metal atoms lost electrons

◦Na loses one electron---Na+

◦Ca loses two electrons –Ca2+

◦By losing electrons, metals can get to the magic number! Usually 8, could be 2


Forming Negative Ions◦Negative ions form when nonmetal atoms gain electrons

◦Cl gains one electron – Cl-◦O gains two electrons – O2-

◦By gaining electrons, nonmetals can get to the magic number! Usually 8, could be 2


Ionic Compounds◦When ionic bonds form, the number of electrons lost by the metal EQUALS the number of electrons gained by the nonmetals Everyone is happy!

◦The overall compound is neutral because the ions cancel out


When ions bond, they form a repeating 3D pattern called a crystal lattice◦Strong bonds mean: High melting points Brittleness High boiling points


Energy Energy is needed to lose an electron. ◦Very little energy is needed for Group I and II elements.

Energy is given off when atoms gain electrons. ◦Group 17 give off the most energy.


Section Review 1. Explain how ionic bonds form

2. Describe how positive ions form

3. Describe how negative ions form

4. Explain why ionic compounds are neutral


Objectives:◦Explain how covalent bonds form

◦Describe molecules◦Explain how metallic bonds form◦Describe the properties of metals

Section 3: Covalent and Metallic Bonds

What are Covalent Bonds◦A covalent bond forms when atoms

share one or more pairs of electrons

◦Occurs between nonmetals◦Helps them get to their MAGIC NUMBER

(8 or 2)


Covalent Bonds and Molecules◦A molecule is the smallest unit of a substance that keeps all the physical and chemical properties of that substance 2 or more atoms joined in a definite ratio


Covalent Bonds and Molecules◦ Easier way to draw them– Electron-Dot Diagrams

Remember, only the valence electrons are important for bonding!


Covalent Bonds and Molecules◦To make an electron-dot diagram:

1. Write the symbol of the element in the center

2. Figure out how many valence electrons it has

3. Add valence electrons NSEW order4. You’re finished!


Section 3: Covalent and Metallic Bonds Examples of electron-dot diagrams

• Models are useful for counting electrons in energy levels. But, these models do not show the true structure of an atom.

Atom v. molecule


Atom Molecule

One type of element Two or more types of elements

Smallest particle into which an element can be divided and still be the same element

Smallest particle into which a covalently bonded compound can be divided and still be the same compound

The Simplest Molecules◦ Must have at least two covalently bonded atoms

2 of the same element? Diatomic molecules Remember: HONClBrIF

Hydrogen Oxygen Nitrogen Chlorine Bromine Iodine Fluorine


More Complex Molecules◦ Many different elements◦ Many based on carbon


Metallic Bonds◦Metals have properties like malleability

and ductility because of their special bonds Metallic bonds are bonds from

between the attraction of positively charged metal ions and the electrons around them


Movement of Electrons Throughout a Metal◦Bonding in metals is a result of the metal

atoms being so close to another that their outermost energy levels overlap

◦Metals surrounded in a “sea” of electrons


Properties of Metals◦Conducting Electric Current Valence electrons that are moving

◦Reshaping Metals Electrons free to move around…makes it easy

to shape Ductility Malleability

◦Bending without breaking Electrons can move in response to pressure so

they can bend without breaking


Alloys

Scientists can design alloys with specific properties by varying the types and amounts of elements in the alloy.

An alloy is a mixture of elements and at least one is a metal. Alloys have properties of metals.

Bronze = copper and tin

Steel = Iron and carbon

Airplanes = Aluminum and copper or manganese.

Section Review

1. Explain how covalent bonds form

2. Describe molecules

3. Explain how metallic bonds form

4. Describe the properties of metals


Chemical Bonding

Documents

Transcript of Chemical Bonding