covalent compounds

Covalent compounds• A covalent compound consists of two

or more nonmetals.

• They are able to bond together by sharing their valence electrons.

Covalent compounds• Atoms will share 1, 2, or 3 pairs of

electrons so that each valence level has a stable octet.

• This sharing of electrons is the bond that keeps the atoms together.

Covalent compounds• Single covalent bond – Atoms share 1

pair of electrons.• Double covalent bond – Atoms share

2 pairs of electrons.• Triple covalent bond – Atoms share 3

pairs of electrons.

Covalent compounds• We can determine how many pairs of

electrons are shared by drawing an Electron-Dot Diagram.

Covalent compounds• Steps for drawing Electron-Dot

Diagrams;• 1.) Add up the number of valence electrons that

each atom brings to the compound.• 2.) Arrange the atoms in the compound next to

each other. If there are more than two atoms in the compound, arrange them symetrically with the atom that was listed first as the central atom.

• 3.) Place 1 pair of electrons between each atom that will be bonded together.

Covalent compounds• Steps for drawing Electron-Dot

Diagrams (cont.);• 4.) Use the remaining electrons to satify the octet

rule for each element in the compound.• 5.) If there are not enough electrons, place

another pair of electrons between 2 atoms.• 6.) If there are extra electrons, place them on the

central atom, even if it already has 8 electrons.

Covalent compounds• Electron-Dot Diagrams;

• Draw the EDD for chlorine gas (Cl2).• Each atom brings 7 valence electrons

for a total of 14 electrons.• Bond the chorine atoms with a single

pair of electrons. Now there are 12 electrons left.

Cl:Cl

Covalent compounds• Electron-Dot Diagrams;

• Place 6 more electrons around each chlorine atom. The Octet Rule is satisfied for both atoms.

Cl:Cl

Covalent compounds• Electron-Dot Diagrams;

• Draw the EDD for bromine (Br2).

Covalent compounds• Electron-Dot Diagrams;

• Draw the EDD for carbon tetrachlorde (CCl4).

Covalent compounds• Electron-Dot Diagrams;

• Draw the EDD for Oxygen gas (O2).

Covalent compounds• Electron-Dot Diagrams;

• Draw the EDD for Nitrogen gas (N2).

Covalent compounds• Electron-Dot Diagrams;

• Draw the EDD for Carbon monoxide (CO).

Covalent compounds• Electron-Dot Diagrams;

• Draw the EDD for carbon dioxide (CO2).

Covalent compounds• Exceptions in drawing Electron-Dot

Diagrams;

• Just like everything else in Chemistry, there are exceptions to the Octet Rule.• Hydrogen – Stable with only 2 valence

electrons.• Boron – Stable with 6 valence electrons.• Sulfur and Phosphorous – Stable with 8, 10,

or 12 valence electrons.

Covalent compounds• Exceptions in drawing Electron-Dot

Diagrams;

• Draw the EDD of Hydrogen Chloride (HCl).

Covalent compounds• Exceptions in drawing Electron-Dot

Diagrams;

• Draw the EDD of boron trifluoride (BF3).

Covalent compounds• Exceptions in drawing Electron-Dot

Diagrams;

• Draw the EDD of phophorous pentachloride (PCl5).

Covalent compounds• Draw the electron dot diagram for

the ammonium ion.

Covalent compounds• Resonant Structures

o Resonant structures are multiple ways of drawing an EDD for a molecule.

o The nitrate ion, NO3-1, has three different ways to

draw its dot diagram;

Covalent compounds• Resonant Structures

o Which molecule has resosnant structures, SO3 or SO3

-2?

Covalent compounds• Coodinate Covalent Bonds

o A coordinate covalent bond forms when one atom donates both electrons that are used to form a covalent bond.

Covalent Compounds

• Naming Covalent Compounds – Prefixes have to be used since different

compounds can have different ratios of the same elements.

mono = 1, di = 2, tri = 3, tetra = 4, penta = 5, hexa = 6, hepta = 7, octa = 8, nona = 9, and deca = 10

Covalent Compounds• Naming Covalent Compounds – Use a prefix to indicate the number of atoms of each

element in the covalent compound and add the suffix ‘ide’ to the name of the last element.

• N2O4 = dinitrogen tetroxide

• P2O10 = diphophorous decoxide

• CO2 = carbon dioxide *• CO = carbon monoxide *

* If there is only one of the first element, don’t use a prefix. It is implied that there is only 1 atom in the compound.

Covalent Compounds• Naming Covalent Compounds – Name these covalent compounds;

• H2O

• CCl4

• CS2

• CCl4

• S2O6

Covalent Compounds• Naming Covalent Compounds – There is a special type of covalent compounds called

acids.

• An acid will always contain hydrogen.

• The hydrogen will be listed first.

• Acids have a different naming system.

Covalent Compounds• Naming Covalent Compounds

– Naming Acids that do not contain oxygen;

• Use the prefix ‘hydro’ on the name of the second element with the suffix ‘ic’.

–HCl = hydrochloric acid

–HF = hydrofluoric acid

–H2S = hydrosulfic acid

–HBr = hydrobromic acid

Covalent Compounds• Naming Covalent Compounds

– Naming Acids that contain oxygen;

• If the anion ends in ‘ate’, then use the suffix ‘ic’ on the name of the anion.

–H2SO4 = sufuric acid

• If the anion ends in ‘ite’, then use the suffix ‘ous’ on the name of the anion.

–H2SO3 = sulfurous acid

Covalent Compounds• Naming Covalent Compounds

– Name these acids;

• HI

• HCl

• H3PO4

• H2C2O4

• HC2H3O2

Covalent Compounds

• VSEPR Theory– Valence Shell Electron Pair Repulsions• Bonding electrons and lone pairs of electrons will repel

themselves so that they will separate by the maximum distance possible.

Covalent Compounds

• VSEPR Theory– Valence Shell Electron Pair Repulsions• The shape of a molecule is determined by these

repulsive forces.

Covalent Compounds

• VSEPR Theory– Valence Shell Electron Pair Repulsions• Linear Shape

– A molecule consisting of just 2 atoms will always be linear.– A molecule with 3 atoms can be linear if there are no lone

pairs of electrons on the central atom.

Covalent Compounds

• VSEPR Theory– Valence Shell Electron Pair Repulsions• Bent Shape

– A molecule that has 3 atoms but there is a lone pair(s) of electrons on the central atom.

Covalent Compounds

• VSEPR Theory– Valence Shell Electron Pair Repulsions• Trigonal Planar Shape

– A molecule that has 4 atoms with no lone pairs on the central atom.

Covalent Compounds

• VSEPR Theory– Valence Shell Electron Pair Repulsions• Trigonal Pyramidal Shape

– A molecule that has 4 atoms with a lone pair of electrons on the central atom.

Covalent Compounds

• VSEPR Theory– Valence Shell Electron Pair Repulsions• Tetrahedral Shape

– A molecule that has 5 atoms with no lone pairs of electrons on the central atom.

Covalent Compounds

• VSEPR Theory– Valence Shell Electron Pair Repulsions• Trigonal Bipyrimidal Shape

– A molecule that has 5 atoms with no lone pairs of electrons on the central atom.

Covalent Compounds

• Bond Polarityo Polar – having two distinct ends.o Sometimes, there is an unequal sharing of the

electrons that make up a covalent bond. As a result, the bonding electrons can spend more time with atom compared to the other one.

Covalent Compounds

• Bond Polarityo The atom with the higher electronegativity value

will have the bonding electrons most of the time.o The atom with the higher electronegativity will

have a partial negative charge (δ-).

Covalent Compounds

• Bond Polarityo The atom with the lower value of electronegativity

will appear to have a positive charge (δ+).

Covalent Compounds

• Bond Polarityo If two bonding atoms have the same

electronegativity, the bond will not appear to be polar.

Covalent Compounds

• Bond PolarityoWhen determining if a molecule is polar or

nonpolar, you must analyze the entire molecule and consider its shape.

o CO2 is nonpolar.

δ- δ+ δ-

O = C = O

Covalent Compounds

• Bond PolarityoWhen determining if a molecule is polar or

nonpolar, you must analyze the entire molecule and consider its shape.

o CCl4 is nonpolar.

Covalent Compounds

• Bond PolarityoWhen determining if a molecule is polar or

nonpolar, you must analyze the entire molecule and consider its shape.

o H2O is polar.

Covalent Compounds

• Bond PolarityoWhen determining if a molecule is polar or

nonpolar, you must analyze the entire molecule and consider its shape.

o HCl is polar.

Covalent Compounds

• Bond PolarityoWhen determining if a molecule is polar or

nonpolar, you must analyze the entire molecule and consider its shape.

o Is NH3 polar or nonpolar?

Covalent Compounds• Bond Polarity

o Electronegativity Table

Covalent Compounds• Are the following compounds polar or non

polar?

o PH3:

o SO3:

o H2S:

o I2:

o CS2:

Covalent Compounds

• Intermolecular Forces– Forces of attraction between 2 or more other

molecules in a substance.

Covalent Compounds

• Intermolecular Forces– 3 types: London Dispersion Forces (weakest),

Dipole-Dipole, and Hydrogen Bonding (strongest).

Covalent Compounds

• Intermolecular Forces– London Dispersion Forces: Weak forces of

attractions caused by the attraction between the protons in one molecules and the electrons in another molecule.

Covalent Compounds

• Intermolecular Forces– Dipole - Dipole Forces: Weak forces of attractions

caused by the attraction between the oppositely charged poles of two or more molecules.

Covalent Compounds

• Intermolecular Forces– Hydrogen Bonding: Forces of attractions between

a hydrogen atom of one molecule and a fluorine, oxygen, or nitrogen, of another molecule.

Covalent Compounds• Intermolecular Forces– Hydrogen Bonding: Forces of attractions between

a hydrogen atom of one molecule and a fluorine, oxygen, or nitrogen, of another molecule.