Ionic and Covalent Bonding

» Atoms bond when their valence electrons interact ˃Atoms with full outermost energy levels are not reactive (Noble Gases)

» 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)

» 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.

» 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.

» Electrons are placed in shells according to rules: ˃1 st shell: can hold up to 2 electrons ˃2 nd shell: can hold up to 8 electrons ˃3 rd shell: can hold up to 18 electrons, but after 8, you move to the 4 th shell

Symbols of atoms with dots to represent the valence-shell electrons H  He:            Li  Be   B   C   N   O  : F  : Ne :                    Na  Mg   Al   Si   P   S  : Cl  : Ar :        

» 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”

Sodium atom Sodium ion Na  – e   Na ( = Ne) 11 p + 11 p + 11 e - 10 e

Magnesium atom Magnesium ion  Mg  – 2e   Mg (=Ne) 12 p + 12 p + 12 e- 10 e

Group 1Group 2Group 13 H + Mg 2+ Al 3+ Li + Ca 2+ Na + Sr 2+ K + Ba 2+

A. Number of valence electrons in aluminum a) 1 e - b) 2 e - c) 3 e - B. Change in electrons for octet a) lose 3e - b) gain 3 e - c) gain 5 e - C.Ionic charge of aluminum a) 3- b) 5- c) 3 +

A. Number of valence electrons in aluminum c) 3 e - B. Change in electrons for octet a) lose 3e - C. Ionic charge of aluminum c) 3 +

Give the ionic charge for each of the following: A. 12 p + and 10 e - a) 0b) 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-

Give the ionic charge for each of the following: A. 12 p + and 10 e - a) 0b) 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-

» 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

» Electrons are transferred in ionic bonding ˃One atom gains electrons (typically nonmetals), and the other atoms loses electrons (typically metals)

» 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 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

» 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 CaF 2 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

» Electricity: ˃Solid ionic compounds don’t conduct electricity ˃When dissolved in water, ionic compounds conduct electricity because the ions are free to move

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

» 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

Note: Partial charges occur with polar 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.

» 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

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

Periodic Table IONIC METAL + NONMETAL = IONIC COVALENT NONMETAL + NONMETAL = COVALENT METAL NONMETAL