Unit 7 Section 2 Notes

Ionic and Covalent Bonding

Atoms and Electrons

» Atoms bond when their valence electrons interact˃Atoms with full outermost energy

levels are not reactive (Noble Gases)

Atoms and Electrons

» Atoms bond when their valence electrons interact˃Atoms with full outermost energy

levels are not reactive (Noble Gases) ˃Atoms with partially filled energy

levels are more reactive (Groups 1-17)» Goal of atoms: have a full octet (Follow

Octet Rule)

Atoms and Electrons

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

» By completing their octet (either gaining or losing electrons), atoms achieve “Noble Gas Status” and have the electron configuration of a noble gas.

Atoms and Electrons

» The positively charged nucleus attracts the negatively charged electrons; this electrostatic force holds 2 atoms together.

» Recall: The strong nuclear force is responsible for holding an ATOM together.

Review of 4 Fundamental Forces

Atoms and Electrons

» 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

Electron 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 Bonds

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

» Metals lose electrons to form POSITIVELY charged ions, or cations˃ Examples: Lithium (Li), Sodium(Na),

Beryllium (Be), Magnesium (Mg)» 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

“Ahh, I just lost an electron!”

“Are you positive?”

“I can’t take this anymore”

Ionic Bonding: One big greedy thief dog!!

Formation 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 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 Charges (Cations)

Group 1 Group 2 Group 13

H+ Mg2+ Al3+

Li+ Ca2+

Na+ Sr2+

K+ Ba2+

Quick Quiz #1

A. Number of valence electrons in aluminuma) 1 e- b) 2 e- c) 3 e-

B. Change in electrons for octeta) lose 3e- b) gain 3 e- c) gain 5 e-

C. Ionic charge of aluminum a) 3- b) 5- c) 3+

Quiz Quiz #1 Answers

A. Number of valence electrons in aluminum

c) 3 e-

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

C. Ionic charge of aluminum c) 3+

Quick Quiz #2

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

a) 0 b) 2+ c) 2-

B. 50p+ and 46 e-a) 2+ b) 4+ c) 4-

C. 15 p+ and 18e-a) 3+ b) 3- c) 5-

Quick Quiz #2

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

a) 0 b) 2+ c) 2-

B. 50p+ and 46 e-a) 2+ b) 4+ c) 4-

C. 15 p+ and 18e-a) 3+ b) 3- c) 5-

Ionic Bonds

» Nonmetals gain electrons to form NEGATIVELY charged ions, or anions˃ Examples: Oxygen (O), Sulfur (S),

Fluorine (F), Chlorine (Cl)» 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 Bonds

» Electrons are transferred in ionic bonding˃One atom gains electrons (typically

nonmetals), and the other atoms loses electrons (typically metals)

Ionic 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 Bonds

Ionic 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 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 Bonds

»Electricity:˃Solid ionic compounds don’t

conduct electricity˃When dissolved in water, ionic

compounds conduct electricity because the ions are free to move

Covalent Bonds

» Covalent Bond: a bond formed when atoms share one or more pair of electrons˃Often made of molecules˃Formed between nonmetal atoms

Covalent Bonds

» There are 2 types of covalent bonds:˃ Nonpolar covalent bonds: electrons are

shared equally; often occurs between 2 atoms of the same element (diatomic molecules)

˃ 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 Bond

Polar Covalent Bond

Note: Partial charges occur with polar covalent bonds

Covalent Bonds

» Covalent bonds form molecules, which tend to have low melting and boiling points ˃This is because their structures often

do not form a crystal lattice» Covalent molecules do not conduct

electricity well.

Structural 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 Ions

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

BONDING SUMMARYHow to tell what type of bond is

holding a molecule together Periodic Table

METAL + NONMETAL = IONICNONMETAL + NONMETAL = COVALENT

METALNONMETAL