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Covalent Bonding

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Covalent Bonds

Recently we worked with IONIC COMPOUNDS which form when positive CATIONS combine with negative ANIONS.

Not ALL compounds involve ions.

In COVALENT BONDING, valence electrons are shared between two atoms. Electrons are NOT transferred from one atom to another, so they do not

develop “+” or “-” charges as do ions.

Generally form between TWO NONMETAL ELEMENTS from

GROUPS 14, 15, 16, and 17 but can involve elements FROM OTHER GROUPS.

Covalent compounds are also called MOLECULAR COMPOUNDS.

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EXAMPLE

Two Hydrogen atoms move close together to SHARE valence electrons.

H + H H H

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For example, NITROGEN and OXYGEN can form several different compounds:

NO NO2 NO3 N2O

N2O2 N2O3 N2O4 N2O5

If we named this NITROGEN OXIDE, which one would we be talking about?

The SAME TWO ATOMS can share DIFFERENT NUMBERS of electrons.

• There is more than one possible formula combination for the same group of atoms.

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Naming Covalent (Molecular) Compounds

In order to name a COVALENT compound, we follow the same basic rules as for BINARY IONIC compounds….with one added step.

Since the same group of atoms can bond in different proportions, we must indicate HOW MANY OF EACH ATOM there is in the compound.

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Naming Covalent Compound

1. Name the first element by its name, adding a NUMBER PREFIX ONLY IF THERE IS MORE THAN ONE ATOM.

2. Name the second element by its name, but:

A. Change the ending to IDE. B. Add a NUMBER PREFIX to tell how

many, even if there is only one!

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Number Prefixes for Covalent Compounds

1 – Mono

2 – Di

3 – Tri

4 – Tetra

5 – Penta

6 – Hexa

7 – Hepta

8 – Octa

9 – Nona

10 –Deca

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When adding prefixes, the “A” or “O” of the prefix may need to be DROPPED if the element starts with a VOWEL, such as:

Hexa added to OXIDE becomes:

Hexoxide NOT Hexaoxide

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Practice Problems

Example Write the formula for:

Trinitrogen Pentachloride

Tri = 3 Penta = 5

nitrogen chloride = chlorine

So this compound needs 3 NITROGEN and 5 CHLORINE

The 3 and 5 are the SUBSCRIPTS in the formula.

N3Cl5

WRITE the formula for these Covalent Compounds:

(To make it easier, prefixes are colored in these practice

problems)

Click HERE for a PERIODIC TABLE.

1. carbon monoxide

2. carbon dioxide

3. phosphorus trichloride

4. carbon tetrachloride

5. dinitrogen monoxide

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1. CO carbon monoxide

2. CO2 carbon dioxide

3. PCl3 phosphorus

trichloride

4. CCl4 carbon tetrachloride

5. N2O dinitrogen monoxide

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MORE PRACTICE PROBLEMS

Write the correct formula for the following Covalent compounds.

1. triphosphorus monoxide2. phosphorus pentoxide3. diphosphorus pentoxide

4. dichlorine heptoxide5. dichlorine tribromide6. silicon tetroxide 7. carbon tribromide

8. antimony disulfide

**STOP HERE**

Diatomic Elements Some elements, when not bonded to other

elements, bond to another atom of their own kind. These are known as DIATOMIC ELEMENTS.

There are 8 naturally existing diatomic elements: ALL of family 17 (Halogen Family). Oxygen, Nitrogen and Hydrogen

These elements should be written as: F2, Cl2, Br2, I2, At2, O2, H2, N2 when they are NOT

part of a compound.

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Pure vs Polar Covalent

When two atoms share an electron, the ELECTRONEGATIVITY value of each atom determines how closely the electron is pulled toward one atom or the other. Recall Electronegativity [Eneg] is the measure of

the attraction one atom has for another’s valence electrons.

SEE CHART NEXT SLIDE FOR Eneg Values.

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Electronegativity Values

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Determining Bond Type To determine the type bond between any two

atoms, find the difference between their Eneg values:

0 to 0.5 - PURE Covalent – the e- is shared at an equal distance between both atoms.

0.51 to 1.99 – POLAR Covalent – the e- is shared closer to one atom than the other…this gives the atom the e- is closest to a slightly NEGATIVE charge [delta -] and the one the e- is father away from a slightly POSITIVE charge [delta +].

2.0 or greater – the e- is completely transferred from one atom to the other and forms an IONIC BOND.

Practice Problems Use Eneg values to predict the type of bond that would form between each

pair of atoms:

1. Ca and Br ____________ 2. H and O ______________ 3. Pb and S ______________ 4. Au and S_______________ 5. Sn and I ______________ 6. C and H _______________

7. B and H _______________ 8. Fr and F _______________ 9. N and Al _______________

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