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 1s22s22p2 or [He]2s22p2

• Valence e- = 2 + 2 = 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 (s2p6)

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

1 s1 1 +1

2 s2 2 +2

13 s2p1 3 +3

14 s2p2 4 NONE

15 s2p3 5 -3

16 s2p4 6 -2

17 s2p5 7 -1

18 s2p6 8 NONE

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– K2O = 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 N3-

– THE CHARGES MUST BALANCE!!– Therefore, there must be 3 lithiums for

every nitrogen = Li3N

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

• CuCl2 = 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: CO32- is called carbonate

• What would the formula for calcium carbonate be? Lithium carbonate? Aluminum carbonate?– CaCO3

– Li2CO3

– Al2(CO3)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 CO2?

• These are different compounds, but how would that be reflected in their name?

• Answer: by using numerical prefixes

Naming Molecules

• The prefixes are: Number Prefix

1 mono

2 di

3 tri

4 tetra

5 penta

6 hexa

7 hepta

8 octa

9 nona

10 deca

Naming Molecules

• CO has one C, one O => carbon monoxide

• CO2 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: P2O5 = diphosphorus pentaoxide

PO5 = 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: HNO3 (anion is nitrate) = nitric acid

• If the ion ends in “ite” the ending changes to “ous” – Ex: HNO2 (anion is nitrite) = nitrous

acid

Naming Hydrates

• Hydrates are compounds that include water (H2O) in their structure

• Ex: CuSO4 ∙ 5H2O– 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 0.5-2.0, 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