4.2COVALENT BONDING

ESSENTIAL IDEACovalent compounds form by the

sharing of electrons.NATURE OF SCIENCE (2.5)

Looking for trends and discrepancies – compounds containing non-metals have different properties than

compounds that contain non-metals and metals.

NATURE OF SCIENCE (2.2)Use theories to explain natural phenomena – Lewis

introduced a class of compounds which share electrons. Pauling used the idea of electronegativity to explain

unequal sharing of electrons.

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UNDERSTANDING/KEY IDEA 4.2.A

A covalent bond is formed by the electrostatic attraction between a shared pair of electrons and the positively charged nuclei.

ELECTRON SHARINGWhen atoms of 2 non-metals react together, each is

seeking to gain electrons in order to achieve the stable electron configuration of a noble gas.

This tendency to form a stable arrangement of 8 electrons in the outer shell is referred to as the octet rule.

The shared pair of electrons is concentrated in the region between the 2 positively charged nuclei.

The electrostatic attraction between the 2 nuclei and the electrons constitutes the covalent bond.

UNDERSTANDING/KEY IDEA 4.2.B

Single, double and triple covalent bonds involve one, two and three shared pairs of electrons, respectively.

UNDERSTANDING/KEY IDEA 4.2.C

Bond length decreases and bond strength increases as the number of shared electrons increases.

BOND LENGTH AND BOND STRENGTHTriple bonds are stronger than double bonds which

are stronger than single bonds.The strength of the bond is a measure of how much

energy is required to break the bond.Triple bonds are shorter than double bonds which

are shorter than single bonds.The number of shared electrons is greater in multiple

bonds causing the electrostatic attraction to be stronger; therefore, causing the bonds to be shorter in length.

A single bond contains only one sigma bond.A double bond contains one sigma and one pi bond.A triple bond contains one sigma and two pi bonds.

UNDERSTANDING/KEY IDEA 4.2.D

Bond polarity results from the difference in electronegativities of the bonded atoms.

APPLICATION/SKILLS

Be able to deduce the polar nature of a covalent bond from electronegativity values.

COVALENT CHARACTERYou can predict covalent character by two ways:

Position on the Periodic TableElectronegativity differences

Position on the Periodic TableCovalent compounds tend to form between 2 non-

metals.The closer together two elements are, the more

covalent.Electronegativity

Electronegativity values are given in Table 8 of the IB Data Booklet.

Differences less than 1.8 are considered to be covalent.

POLARITYA bond that is unsymmetrical with respect to

electron distribution is said to be polar.The term dipole means the bond has an area of

positive charge and an area of negative charge. (delta symbol)

The Pauling scale predicts polarity by using electronegativity differences.

Values of 0.0-0.4 are considered non-polar covalent.Values between 0.4 and 1.8 are considered polar

covalent.Values greater than and equal to 1.8 are considered

ionic.Basically, the greater the electronegativity

difference, the more polar the bond.

GUIDANCE

Bond polarity can be shown either with partial charges, dipoles or vectors.

GUIDANCE

Electronegativity values are given in the data booklet on page 8.

CitationsInternational Baccalaureate Organization. Chemistry Guide, First assessment 2016. Updated 2015.

Brown, Catrin, and Mike Ford. Higher Level Chemistry. 2nd ed. N.p.: Pearson Baccalaureate, 2014. Print.

Most of the information found in this power point comes directly from this textbook.

The power point has been made to directly complement the Higher Level Chemistry textbook by Catrin and Brown and is used for direct instructional purposes only.