Unit #3:

Every element wants to be “happy” (have their outer energy level full) An element can accomplish this in one of two ways: 1) Electrons can be exchanged from one element to another so that they both become happy. 2) Electrons can be shared between elements so that they both become happy. * Elements that become happy by exchanging electrons with other elements form an ionic bond with that element. * Elements that become happy by sharing electrons with other elements form a covalent bond with that element

1.An ionic bond occurs between a metal and a nonmetal 2.An ionic bond occurs when electrons are exchanged from one element to another (usually a nonmetal TAKES electrons from a metal) * The nonmetal has a higher electron affinity (the ability of an element to attract electrons) because it is closer to being “happy”; therefore, it takes an electron(s) away from the metal so that they both become happy. 3.An ionic bond IS NOT a physical bond, rather an attraction (closeness) between ions of opposite charge. Example: Na +1 and Cl -1

Ionic Bonding Examples… Let’s see how Potassium might become happy Lets’ see how Fluorine might become happy What does Potassium want to do in order to become happy? Wants to lose its one valence electron What would be the ionic charge for Potassium? +1 (because it lost one electron) What does Fluorine want to do in order to become happy? Wants to gain one valence electron What would be the ionic charge for Fluorine? -1 (because it gained one electron) What will happen between these two ions? Opposite charges attract. Thus, these two ions will form an ionic bond. (Loses electrons) (Gains electrons)

Naming Ionic Compounds is quite simple… All you do is put the metal name first and the nonmetal name second (the end of the nonmetal name changes to –ide). Using our last example (with potassium and fluorine), let’s do an example of how to name an ionic compound K +1 F -1 The metal goes 1 st and nonmetal goes 2 nd (-ide ending) Potassium Fluoride The chemical equation for this ionic compound is K 1 F 1 or simply KF because it takes 1 potassium to make 1 fluorine happy.

Let’s Do Another Example… MagnesiumSulfur How does Magnesium become happy?How does Sulfur become happy? Magnesium wants to lose its outer 2 electrons (ionic charge of +2) Sulfur wants to gain 2 electrons (ionic charge of -2) Sulfur took 2 electrons from Magnesium (because Sulfur has a higher electron affinity). Therefore, the two ions attract because of their opposite charges. Ionic compound is called Magnesium Sulfide; Chemical formula is MgS

Up until this point, all elements formed an ionic bond that had equal and opposite ionic charges (Example: Mg +2 and S -2 ). What happens if different elements form different ionic charges? Will they still form an ionic bond? LithiumPhosphorus We will use Lewis Dot Structures to show how this will work. Lewis dot structures plot ONLY the valence electrons of an element Li P It takes 3 Lithium atoms to make 1 Phosphorus atom happy. Phosphorus takes the 1 valence electron from 3 different lithium atoms to become happy. Therefore, the chemical formula is Li 3 P (name is Lithium Phosphide)

BerylliumNitrogen BeN N It takes 3 Beryllium atoms to make 2 Nitrogen atoms happy. You can see that the charges on the Beryllium atom equals +6 and the charges on the Nitrogen atom equals -6. The chemical formula for the above ionic compound is: Be 3 N 2 The name of the ionic compound is: Beryllium Nitride

Instead of using Lewis Dot Structures to show how two elements become happy, there is a much easier way… 1.Find the ionic charge of both given elements 2.Drop the charge (+ or -). 3.Criss-Cross (or swap) the numbers from one element to the other. (see examples below) 4.Superscript #’s become subscripts (don’t have to write 1’s) Mg +2 F -1 Mg 2 F 1 MgF 2 Na +1 P -3 Na 1 P 3 Na 3 P Al +3 O -2 Al 3 O 2 Al 2 O 3

1.A covalent bond occurs between 2 nonmetals OR between a nonmetal and hydrogen. 2.A covalent bond occurs when 2 nonmetals or a nonmetal and hydrogen share electrons to make one another happy. 3.A covalent bond IS a physical bond because the elements share electrons Electron affinity of all nonmetals and hydrogen are relatively the same. Therefore, they are not strong enough to take away electrons from another element. Thus, they share electrons.

Covalent Bonding Examples… FluorineChlorine We must first determine how many bonds each element is capable of forming! 2 electrons = 1 bond To find out how many bonds each element is capable of forming, you subtract the number of valence electrons the element has from the total number of electrons that it wants in the outer energy level. (see below) Fluorine Needs:8 electrons Fluorine has:-7 electrons 1 bond Chlorine Needs:8 electrons Chlorine has:-7 electrons 1 bond F Cl

Hydrogen & HydrogenHydrogen & Oxygen How many bonds will Hydrogen form? How many bonds will Oxygen form? Hydrogen needs : 2 electrons Hydrogen has : -1 electron 1 bond (See bond # at left) Oxygen needs:8 electrons Oxygen has: -6 electrons 2 bonds H H H O H HHO

Nitrogen & Nitrogen How many bonds will one atom of Nitrogen form? Nitrogen needs:8 electrons Nitrogen has:-5 electrons 3 bonds N N N Carbon & Hydrogen How many bonds will each atom form? Carbon needs:8 e- Carbon has:-4 e- 4 bonds Hydrogen needs: 2 e- Hydrogen has: -1 e- 1 bond C H H H HC H HH H

Carbon & Oxygen Figure out how many bonds each atom is capable of forming. Carbon needs:8 e- Carbon has:-4 e- 4 bonds Oxygen needs:8 e- Oxygen has:-6 e- 2 bonds C O O COO