Chapter 4 Section 2 Notes

Ionic and Covalent Ionic and Covalent BondingBonding

What holds bonded atoms together?What holds bonded atoms together?

Atoms bond when their valence electrons interact– Atoms with full outermost energy levels are less

reactive (Noble Gases) – Atoms with partially filled energy levels are more

reactive (Groups 1-17)

Goal of atoms: have a full outer energy level

What holds bonded atoms together?What holds bonded atoms together?

Octet Rule: atoms tend to gain, lose, or share electrons so they have 8 electrons in their outer shell.

The positively charged nucleus attracts the negatively charged electrons; this bond holds 2 atoms together.

Bonds behave like flexible springs instead of like sticks

Electrons in ShellsElectrons in Shells

Electrons are placed in shells according to rules:– 1st shell: can hold up to 2 electrons– 2nd shell: can hold up to 8 electrons– 3rd shell: can hold up to 18 electrons, but after 8,

you move to the 4th shell

Na would like to: lose 1 electron N would like to: gain 3 electrons O would like to: gain 2 electrons

Electron Dot DiagramsElectron Dot Diagrams

Symbols of atoms with dots to represent the valence-shell electrons

1 2 13 14 15 16 17 18H He:

Li Be B C N O : F :Ne :

Na Mg Al Si P S :Cl :Ar :

Ionic BondsIonic Bonds

Ionic Bond: formed when metals react with nonmetals; electrons are transferred

Metals lose electrons to form POSITIVELY charged ions, or cations

– Examples: Lithium, Sodium, Beryllium, Magnesium Positive ions form when the number of electrons are

less than the number of protons– Group 1 metals → ion+1

– Group 2 metals → ion+2

– Group 13 metals → ion+3

Ionic Bonding: One big greedy thief dog!!

Formation of Sodium IonFormation of Sodium Ion

Sodium atom Sodium ion

Na – e Na +

2-8-1 2-8 ( = Ne)

11 p+ 11 p+

11 e- 10 e-

0 1+

Formation of Magnesium IonFormation of Magnesium Ion

Magnesium atom Magnesium ion

Mg – 2e Mg2+

2-8-2 2-8 (=Ne)

12 p+ 12 p+

12 e- 10 e-

0 2+

Some Typical Ions with Positive Some Typical Ions with Positive Charges (Cations)Charges (Cations)

Group 1 Group 2 Group 13

H+ Mg2+ Al3+

Li+ Ca2+

Na+ Sr2+

K+ Ba2+

Quick Quiz #1Quick Quiz #1

A. Number of valence electrons in aluminum1) 1 e- 2) 2 e- 3) 3 e-

B. Change in electrons for octet1) lose 3e- 2) gain 3 e- 3) gain 5 e-

C. Ionic charge of aluminum 1) 3- 2) 5- 3) 3+

Quiz Quiz #1 AnswersQuiz Quiz #1 Answers

A. Number of valence electrons in aluminum3) 3 e-

B. Change in electrons for octet1) lose 3e-

C. Ionic charge of aluminum 3) 3+

Quick Quiz #2Quick Quiz #2

Give the ionic charge for each of the following:A. 12 p+ and 10 e-

1) 0 2) 2+ 3) 2-

B. 50p+ and 46 e-

1) 2+ 2) 4+ 3) 4-

C. 15 p+ and 18e-

2) 3+ 2) 3- 3) 5-

Ionic BondsIonic Bonds

Nonmetals gain electrons to form NEGATIVELY charged ions, or anions– Examples: Oxygen, Sulfur, Fluorine, Chlorine

Negative ions form when the number of electrons is more than the number of protons– Group 15 nonmetals → ion-3

– Group 16 nonmetals → ion-2

– Group 17 nonmetals → ion-1

Ionic BondsIonic Bonds

Electrons are transferred in ionic bonding– One atom gains electrons, and the other atoms

loses electrons

Ionic BondsIonic Bonds

Example: Sodium loses one electron to get a +1 charge (Na+). Chlorine gains an electron to get a -1 charge (Cl-). Then, the oppositely charged ions attract each other and form a bond.

Ionic BondsIonic Bonds

Ionic BondsIonic Bonds

Ionic compounds are in the form of network structures; they therefore have high melting and boiling points because of the high amount of energy required to pull apart the bonds

Ionic BondsIonic Bonds

Ratio of Ions – The chemical formula NaCl tells us there is 1 Na+

ion and 1 Cl- ion, forming a neutrally charged particle.

Since there is only one atom of each element, there is a 1:1 ratio

– The chemical formula CaF2 tells us there is 1 Ca+2 ion and 2 F- ions. 2 F- ions are needed to balance out the +2 charge so the particle is neutral

Ionic BondsIonic Bonds

Electricity:– Solid ionic compounds don’t conduct electricity– When dissolved in water, ionic compounds

conduct electricity because the ions are free to move

Metallic Bonds

Metallic Bond: a bond formed by the attraction between positively charged metal ions and the electrons around them. – Occurs between atoms of metal elements

Metallic Bonds

The attraction between the nucleus and the neighboring atom’s electrons holds the atoms close together

Since the atoms are packed closely, the electrons move from atom to atom, which is why:– Metals conduct electricity– Metals are flexible and bend without breaking

(ductile and malleable)

Covalent BondsCovalent Bonds

Covalent Bond: a bond formed when atoms share one or more pair of electrons– Often made of molecules– Formed between nonmetal atoms– Atoms joined by covalent bonds share electrons

Covalent BondsCovalent Bonds

There are 2 types of covalent bonds:– Nonpolar covalent bonds: electrons are shared

equally; often occurs between 2 atoms of the same element

– Polar covalent bonds: electrons are shared unequally; often occurs between 2 atoms of different elements; shared electrons are attracted to the nucleus of 1 atom more than the other

Usually, electrons are more attracted to atoms of elements located to the right and closer to the top of the periodic table

Nonpolar Covalent BondNonpolar Covalent Bond

Polar Covalent BondPolar Covalent Bond

Note: Partial charges occur with polar covalent bonds

Structural FormulasStructural Formulas

When writing structural formulas:– 1 line drawn indicates that atoms share 1 pair, or

2 electrons Example: Cl-Cl

– 2 lines drawn indicate that atoms share 2 pair, or 4 electrons

Example: O=O

– 3 lines drawn indicate that 3 pair, or 6 electrons are being shared

Polyatomic IonsPolyatomic Ions

A polyatomic ion is an ion made of 2 or more atoms that are covalently bonded and that act like a single ion

Some polyatomic anion names relate to their oxygen content– An anion ending in –ate is the ion with one more

oxygen atom– An anion ending in –ite is the ion with one less

oxygen atom Examples: Sulfate (SO4

-2) and Sulfite (SO3-2)