Chemical Formulas and Bonding

Chapter 7

Ionic Bonding

• In an ionic bond, a positively charged ion is attracted to a negatively charged ion.– Ionic compounds are composed entirely of ions.

• Cations are positively charged ions• Anions are negatively charged ions

• Ionic compounds are electrically neutral, so the electrical charges of the cations and anions must balance.– Example: NaCl

• The Octet Rule – atoms tend to gain, lose, or share electrons in order to acquire a full set of valence electrons (8 in the s and p orbital, except hydrogen and helium)

Electron moves here!

• Lewis Dot Diagrams or Electron Dot Diagrams – Valence electrons are represented as dots placed around the element symbol. Small x’s or o’s can also be used instead of dots.

Sodium

• Types of Ions– Monatomic Ions – made up of one atom

– Cations are named according to the element name– Anions are named according to the element name, but add

“ide” to the end

• Monatomic cations and anions examples:

– Polyatomic ions – made from more than one atom

• Polyatomic cations and anions examples:

– Binary Ionic Compounds – compound which contains only two elements

• Empirical formula – ratio of ions in a compound

• Examples:

• Na+1 Cl-1 Na1+Cl1- NaCl

• Ca+2 F–1 Ca+2 F–1 Ca1F2 CaF2

Covalent Bonding

• Formed by a shared pair of electrons between two non-metal atoms– Molecule – a group of atoms that are united by

covalent bonds• Molecular substance – a substance that is made of

molecules

• Molecular formula – tells how many atoms are in a single molecule of the compound.

• Structural Formula – specifies which atoms are bonded to each other in a molecule

• Lewis structures – based on the Lewis dot diagrams for atoms

• Lewis structures can be drawn using either dots or dashes. – Each dot represents an

electron– Dashes represent a pair

of electrons– Lone pairs are electrons

that are not used in covalent bonding.

– Bonding pairs are the shared electrons between atoms.

• Ammonia NH3

• made up of a covalent bond between nitrogen and hydrogen

• Each atom in the bond has a stable electron configuration ~ hydrogen only needs 2 electrons, but nitrogen needs 8.

Carbon tetrachloride CCl4

– Carbon and chlorine both have a stable octet of electrons surrounding them.

• Multiple Bonds – bonds between atoms where more than two electrons are shared– Single covalent bond – one pair of electrons are

shared– Double covalent bond – two pair of electrons

are shared – Triple covalent bond – three pair of electrons

are shared

• Methane – single covalent bonds between hydrogen and carbon

• Ethyl Alcohol, Ethanol C2H5OH– single covalent bonds between hydrogen, carbon and oxygen

• Carbon dioxide – double covalent bond between carbon and oxygen, giving each element an octet

• Oxygen gas – double covalent bond between oxygen atoms, giving each an octet

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• Cyanic acid – triple covalent bond between carbon and nitrogen, giving each an octet. Hydrogen only needs two to be stable!

• Nitrogen gas – triple covalent bond between nitrogen atoms, giving each an octet.

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• Nonpolar covalent bonds occur when atoms exert an approximately equal pull on the electrons in the bond.

• Exceptions to the octet rule cause bonding that is unusual.

B

F

F F

Naming Chemical Compounds

• Compounds are named according to the atoms and bonds that compose it

• Ionic compounds are named based on the ions that are involved– Cations are named according to their element name– Anions are named according to their element, but the

ending is changed to “ide” or polyatomic ion name• Example: KI is called potassium iodide, not

potassium iodine

– Cu(NO3)2 is called copper II nitrate

• Molecular Compounds are named similar to ionic compounds, except for the anion.– First element is named

according to the element name. If it has more than one of that element, then you must use a prefix

– Second element is named according to the element name, plus the “ide” ending, but depending on the number of atoms of that element, a prefix must be used

• Example: CO2 is called carbon dioxide, because of the 2 oxygen atoms

Prefix Number Mono- 1 Di- 2 Tri- 3 Tetra- 4 Penta- 5 Hexa- 6 Hepta- 7 Octa- 8 Nona- 9 Deca- 10

• Naming acids depends on the ions that make up the acid– Diatomic compounds, such as HF, are named first by

hydro for the hydrogen, then fluoride for the fluorine – However, fluoride is changed to fluoric, giving the

name hydrofluoric acid– Acids containing polyatomic ions do not have hydro

as a prefix, but are named according to the polyatomic ion

• The ending for the ion depends on the number of oxygen atoms or the name of the polyatomic ion

• Example: HNO3 is called nitric acid, but HNO2 is called nitrous acid

• ate = ic• ite = ous• At the right

are common acids and their anions

Anion Corresponding acid

Anion Corresponding acid

F-, fluoride

HF, hydrofluoric acid

NO3-,

nitrate HNO3, nitric acid

Cl-, chloride

HCl, hydrochloric acid

CO3-2,

carbonate

H2CO3, carbonic acid

Br-, bromide

HBr, hydrobromic acid

SO4-2,

sulfate H2SO4, sulfuric acid

I-, iodide

HI, hydroiodic acid

PO4-3,

phosphate

H3PO4, phosphoric acid

S-2, sulfide

H2S, hydrosulfuric acid

C2H3O2-, acetate

HC2H3O2, acetic acid

Sulfate = sulfuricPhosphate = phosphoric