Chemical Bonding

Electron Configuration in Ionic Bonding Valence Electrons are electrons in the highest occupied energy level of an atom These electrons determine the chemical properties of an element

Electron Configurations in Ionic Bonding Valence electrons can be determined by looking at the element’s electron configuration Ex: carbon is 1s 2 2s 2 2p 2 or [He]2s 2 2p 2 Valence e - = = 4

Electron Configurations in Ionic Bonding Valence electrons are usually the only ones used in bonding These can be shown on electron dot structures

Electron Configurations in Ionic Bonding Octet Rule – in forming compounds, atoms tend to achieve the electron configuration of a noble gas All noble gases (except He) have eight valence electrons (s 2 p 6 )

Electron Configurations in Ionic Bonding Metals (elements on the left side of the periodic table) tend to form cations This is because it is easier to lose 1,2,3 or electrons than to gain 5,6,7

Electron Configurations in Ionic Bonding Nonmetals (elements on the right side of the periodic table) tend to form anions This is because it is easier to gain 1,2,3 electrons than to lose 5,6,7

Electron Configurations in Ionic Bonding Group #Electron Config Valence electrons Ionic Charge 1s1s s2s s2p1s2p s2p2s2p2 4NONE 15s2p3s2p s2p4s2p s2p5s2p5 7 18s2p6s2p6 8NONE

Formation of Ionic Bonds An ionic bond is the transfer of electrons, which results in two ions of opposite charge attracting to one another Ex: Na will give up one electron to Cl so that you have Na + and Cl -, which are then attracted to one another forming NaCl

Naming Ions Cations: same element name, just add the word “ion” on the end –Ex: Na + = sodium ion Anions: change the ending to “-ide” and add the word “ion” on the end –Ex: Cl - = chloride ion

Naming Ionic Compounds When naming an ionic compound, name the cation, then the anion (left to right) –Ex: NaCl = sodium chloride –K 2 O = potassium oxide –The fact that there are numbers doesn’t affect anything (unless they are transition metals)

Naming Ionic Compounds To go from the name to the symbols, you need to know the ionic charges: –Ex: give the symbol for lithium nitride –Lithium is Li + and nitride is N 3- –THE CHARGES MUST BALANCE!! –Therefore, there must be 3 lithiums for every nitrogen = Li 3 N

Naming Ionic Compounds Transition metals usually form more than one cation When naming compounds containing transition metals, a roman numeral is used to indicate the charge Ex: CuCl = copper (I) chloride CuCl 2 = copper (II) chloride

Naming Ionic Compounds Polyatomic Ions – an ion consisting of more than element; all of these elements work together as one “unit” and the entire “unit” has a specific charge These have special names that need to be memorized Naming is done in the same fashion

Naming Ionic Compounds Ex: CO 3 2- is called carbonate What would the formula for calcium carbonate be? Lithium carbonate? Aluminum carbonate? –CaCO 3 –Li 2 CO 3 –Al 2 (CO 3 ) 3 CHARGES MUST STILL BE BALANCED

Covalent Bonding Covalent Bonding takes place between two non-metals and involves a sharing of electrons to obtain an octet Electrons that do not take place in the bond are called unshared pairs

Covalent Bonding Sometimes atoms will form multiple bonds to achieve stable configurations Double bonds involve 4 electrons being shared, and triple bonds involve 6 electrons being shared

Covalent Bonding Single bonds are the longest, followed by double, then triple Triple bonds are the strongest, followed by double, then single

Covalent Bonding Some elements are typically found in nature covalently bonded to another atom of the same element. These are called diatomic elements Ways to remember these 7: –BrINClHOF (brinkelhoff) –I Bring Clay For Our New House

Naming Molecules Covalent compounds are also known as molecules. Unlike ionic compounds, which would only form in one way, many different molecules can form from the same elements

Naming Molecules For example, what is the difference between CO and CO 2 ? These are different compounds, but how would that be reflected in their name? Answer: by using numerical prefixes

Naming Molecules The prefixes are: NumberPrefix 1mono 2di 3tri 4tetra 5penta 6hexa 7hepta 8octa 9nona 10deca

Naming Molecules CO has one C, one O => carbon monoxide CO 2 has one C, two O => carbon dioxide

Naming Molecules Both elements in the compound need to have a prefix – unless the first one is mono, then it can be dropped Ex: P 2 O 5 = diphosphorus pentaoxide PO 5 = phosphorus pentaoxide (no mono needed on the first element)

Naming Acids Acids are compounds that contain a hydrogen ion, and their name comes from the anion to which the hydrogen is bonded If it is bonded to a monatomic ion, the prefix hydro is added and the ending becomes “ic”: HCl is hydrochloric acid

Naming Acids If the anion is a polyatomic ion, no hydro prefix is added. If the ion ends in “ate” the ending changes to “ic” –Ex: HNO 3 (anion is nitrate) = nitric acid If the ion ends in “ite” the ending changes to “ous” –Ex: HNO 2 (anion is nitrite) = nitrous acid

Naming Hydrates Hydrates are compounds that include water (H 2 O) in their structure Ex: CuSO 4 ∙ 5H 2 O –Name the base portion first = copper (II) sulfate –Name the hydrate portion second = pentahydrate –Copper (II) sulfate pentahydrate

Metallic Bonding Bonds between metals atoms are called metallic bonds A metallic bond consists of the positive nuclei of the metal atoms in a “sea” of electrons

Properties of Ionic Compounds Ionic compounds tend to be: –Hard –Brittle –Have high boiling/melting points

Properties of Molecules Molecules can be either polar or nonpolar In a polar covalent bond, electrons are shared unequally In a nonpolar covalent bond, electrons are shared equally

Properties of Molecules Polarity of bonds can be determined using electronegativity differences (listed in a table) If the difference is 0-0.4, the bond is nonpolar covalent. If the difference is , the bond is polar covalent. If the difference is 2.1 or greater, the bond is ionic

Properties of Metals Metals are: –Shiny –Malleable (can be hammered into shapes) –Ductile (can be drawn out into wires)

Properties of Metals Alloys are mixtures of metals that have properties of both metals –Ex: bronze, brass, sterling silver