WHAT IS CHEMICAL BONDING?

Section 5-11

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Chemical Bonding

What is chemical bonding? There are 118 (or more) elements, which combine in

millions of different ways to form compounds. Compounds are more than one kind of atom

chemically combined. Chemical bonding is the combining of atoms to form

new substances.

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Electrons and Energy Levels

An atom has a positively charged nucleus containing protons and neutrons. (p+ are positive, n0 are neutral)

Outside the nucleus is the electron cloud, which contains the negative electrons. The atom itself is neutral, so the number of p+ must

equal the number of e-.

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Electrons and Energy Levels

The electron cloud has Energy levels and electrons are arranged in these levels. The lowest or the first level can hold only 2 e-. The second can hold only 8 e-. The third can hold only 18e-. The fourth can hold only 32e-.

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Electrons and Energy Levels

The electrons in the highest (outermost) Energy level are called valence electrons. They determine how atoms will combine. When the highest Energy level of an atom is full, those

atoms are very stable and do not combine with other atoms by forming chemical bonds.

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Electrons and Energy Levels

Remember that elements in the same family have the same number of valence electrons. Family 18, the Noble Gases, all, except He, which has

2, have 8 valence electrons and do not react or combine with anything.

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Electrons and Bonding

An atom will bond with another if bonding gives both atoms complete outermost Energy levels.

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IONIC BONDING

Section 5-28

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Ionic Bonding

One way for atoms to become stable is to transfer electrons from one to the other. This kind of bonding is called ionic bonding. Ionic bonds are made from ions, which are atoms with

a plus or minus charge. Ions with a “-” charge are called anions. Ions with a “+” charge are called cations.

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Ionic Bonding

When atoms transfer electrons, one loses and one gains.

Atoms that lose e- have a positive charge.Atoms that gain e- have a negative charge.

Ex: Na has 11p+ and 11e-, it loses 1e- giving it 11p+ and 10e-. This gives it a 1+ charge (Na+)

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Energy for Ion Formation

In order for an electron to be removed from an atom, its attraction to the nucleus must be overcome. The process of removing electrons and forming ions is

called ionization. The energy needed for ionization is called the

ionization Energy. This Energy is low for atoms with only a few valence

electrons, so they lose electrons easily.

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Energy for Ion Formation

The ionization Energy for atoms with a lot of valence electrons is high.

It is so high, in fact, that these atoms gain electrons instead of losing them.

The tendency of an atom to attract electrons is called electron affinity.

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Energy for Ion Formation

What ions would the following make? K (it has only 1 valence e-, so it will lose it becoming

K+). Ca (it has 2 valence e-, so it will lose them both

becoming Ca2+). Ga = Ga3+

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Polyatomic Ions

Certain ions are made from atoms that tend to stay together, but they have a charge.

These are called polyatomic ions.See figure 7-18 on page 186.Ions come together to form neutral

molecules!!! (*compounds*).

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Combining Ions

Ions come together to form neutral molecules!!! (*compounds*).

What compounds would form? Ga3+ and Nitrate (NO3

1-) Ga(NO3)3

Ca2+ and Phosphate (PO43-)

Ca3(PO4)2

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Sectio

n 5-3

COVALENT B

ONDS

Covalent Bonds

Bonds that occur between atoms who neither lose or gain electrons easily. In these cases, no electrons are transferred, only

shared. Bonds formed with shared electrons are called

covalent bonds.

Covalent Bonds

By sharing, each atoms fills up its outer most Energy level because the shared electrons are in the outermost Energy level of both atoms at the same time. Ex: H2 each H has 1 valence e-, each wants two so

they can share their electrons and both be happy.

Electron Dot DiagramsUsed to represent electron sharing.Also known as Lewis Dot Structures.These diagrams are chemical symbols with dots around it, representing the valence electrons.

Formation of Molecules

A combination of atoms formed by a covalent bond is called a molecule which is the smallest part of a compound. Compounds are represented by chemical formulas. Subscripts tell how many atoms of each element. Ex: H2O- 2 H and 1 O

Covalent Properties

Covalently bonded solids have low melting points. (most)

Some form network solids- very large molecules. Ex: diamonds and sand- these have high melting

points.

Section 5-4

METALLIC BONDS

Metallic Bonds

A metallic solid is a solid made of only one element.

These are made with metallic bonds. In metallic bonds, the outer electrons of the

atoms form a common electron cloud often called a “sea of electrons.”

Having this “sea of electrons” is responsible for many of the metal properties like malleability, ductility because the metal atoms can slide over one another easily, yet still be held together.

It also allows for easy conduction.

Section 5-5

PREDICTING TYPES OF BONDS

Predicting Bonds

When the elements in the bond are on the Periodic Table will help you predict which kind of bond will form.

Metals (when by themselves) will have metallic bonds.

Compounds formed between elements that lose e- easily and those that gain e- easily will have ionic bonds. Metals tend to lose easily. Nonmetals tend to gain easily. Bonds between the two tend to be ionic bonds.

Predicting Bonds

Compounds formed between elements that have similar tendencies to gain electrons will have covalent bonds. Bonds between nonmetals will be covalent.

Combining Capacity of Atoms

The number of valence electrons determines how an atom will combine with other atoms.

Knowing how many valence electrons an atom has helps you determine how many electrons it will gain or lose when it forms a compound.

The number of valence e- an atom gains or loses is its oxidation number. Ex: Na has 1 valence e-, it can lose 1 or gain 7. It

will lose 1 giving it a 1+ charge. (Na1+). Cl has 7 valence e-, it will gain 1, giving it a charge of Cl1-.