Chapter 5: The Structure of Matter

Section 1: Ionic Bonds

•Bonding of atoms–When two or more atoms join, a bond forms.

•Bonded atoms are the source of all substances. •The kinds of elements in the bond determines the properties of the substance formed.

•Compounds are made from bonded atoms.

The Structure of Matter

•When a metal element bonds with a nonmetal element, an ionic bond is formed.

–Definition: ionic bond – a bond between oppositely charged ions.

–Example:–Sodium has only 1 valence electron.

•Sodium wants to LOSE this electron!

–Chlorine has 7 valence electrons.•Chlorine wants to GAIN an electron!

SO….

Ionic Bonds

You need this example in your notes.

The Structure of Matter

Na

Has one extra…

. Cl....

. ..Needs one more…

The Structure of Matter

Na

The two atoms will BOND.

.Cl....

. ..Now Sodium’s 2nd Energy Level has 8…

1+ 1-

And Chlorine’s 3rd Energy Level has 8.

You need this example in your notes.

–When these two elements bond, Chlorine steals the electron from sodium.

•Now Sodium has a positive charge and has 8 valence electrons. It is now “happy”.

–Chlorine now has a neg. charge. •It has 8 valence electrons, and is “happy”.

•The + and – ions attract each other and form the compound “sodium chloride”.

Electron Transfer!

•Ionic compounds are usually brittle, and crumble easily.

–They also have high melting temperatures..

Ionic Compound Properties

•Ionic compounds can conduct electricity in water.

–When dissolved in water, the ions come apart.–This allows electricity to flow through them.

Ionic Compound Properties

+

+

+

+

+

-

--

-

-

-

•Now that we know how and why ionic bonds form, we can write chemical formulas.•Definition: chemical formula – a method of showing the elements that make up a compound.

–Example: Na1Cl1 tells us that:•Salt is made up of 1 Sodium atom and 1 Chlorine atom.

•What about MgF2 ?

•It is made up of ____ Magnesium atoms and ____ Fluorine atoms.

Writing Ionic Compound Formulas

•Lets take a closeer look at those compounds.

–Na has a charge of 1+, right?

–Cl has a charge of 1_, right? •The charges cancel out!

–When an ionic compound forms, it must have the same number of + and _ charges to be neutral.

Ionic Compound Formulas

•Lets look at how Magnesium and Fluorine bond...

Ionic Compound Formulas

MG2+

Magnesium Ion

F1-

Fluorine Ion

To make a compound with them, you have to make sure the charges cancel.

MG2+

F1-

F1- It takes 1 Magnesium (Mg1)It takes 2 Fluorine (F2) MgF2

Chapter 5: The Structure of Matter

Section 2: Covalent Bonds

Sugar is a covalent compound.

• When a bond forms between two nonmetal elements, it is called a Covalent Bond.– Water and sugar are two examples of covalent compounds.– Salt is an ionic compound. – Salt does NOT have molecules.

– A covalent bond is formed when atoms share one or more PAIRS of electrons.

– Covalent bonds are formed in order to fill the outer energy level.

Covalent Bonds

• Most covalent compounds have relatively low melting temperatures.

• Covalent compounds do not conduct electricity when melted or dissolved.

•Molecules are not made up of ions, so they have no charge.

•Since molecules have no charge, electricity cannot flow through them.

•Sugar melts easily to become caramel!

Properties of covalent compounds.

• Some nonmetal elements can form covalent bonds with themselves– For example:– Oxygen can bond with other oxygen atoms

by forming covalent bonds.– The atoms will share bonds with each other in

order to become happy.

Covalent Bonds

O.O

.... __...

Each line represents 2 SHARED electrons.

....This is the dot diagram for the O2 Molecule.

• Covalent bonds make molecules.– The simplest molecule is H2.

• When a molecule is made up of only 2 atoms, it is called “diatomic”.– There are 7 elements that make

diatomic molecules with themselves naturally.

Covalent Bonds

The Diatomic Elements

• The 7 Diatomic Elements are:– Hydrogen – H2

– Nitrogen – N2

– Oxygen – O2

– Fluorine – F2

– Chlorine – Cl2– Bromine – Br2

– Iodine – I2

• In order to name a covalent compound, you add a prefix to the element names.– The prefix you add depends on how

many atoms are in the compound.

– The element with the most atoms comes 2nd.

– If the 1st element only has 1 atom, it doesn’t get a prefix.

Naming Covalent Compounds

• Here are the prefixes for naming covalent compounds:– 1 – Mono– 2 – Di– 3 – Tri– 4 – Tetra– 5 – Penta– 6 – Hexa– 7 – Hepta– 8 – Octa– 9 – Nona– 10 - Deca

•The Compound CO2 has:–1 Carbon atom.

•It does NOT get a prefix. Too bad, Carbon.

–2 Oxygen atoms•It gets the prefix “Di”

•Our compound is called…•Carbon Di-Oxide!

Example…

• The Compound N2O5 has:– 2 Nitrogen atoms.

•It gets the prefix “Di”

– 5 Oxygen atoms•It gets the prefix “Penta”

•Our compound is called…•Di-Nitrogen Pent-Oxide (the a was

dropped)

Example…

• Sometimes, compounds are not just ionic or covalent…they can have both kinds of bonds.– Definition: polyatomic ions – groups of

covalently bonded atoms joined by ionic bonds.

– Polyatomic ions are written in parentheses.• For example: Hydroxide is (OH).• Cyanide is (CN)

• Carbonate is CO3

• The compound Sodium Hydroxide would be written as Na(OH)