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Chapter 6: Chemical Bonds. Section 2: Covalent Bonds, Polar and Non Polar Molecules. Covalent - The other type of bond. Many elements do not easily donate or receive electrons. Instead they share them with another atom.
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Chapter 6: Chemical Bonds Section 2: Covalent Bonds, Polar and Non Polar Molecules
Covalent - The other type of bond • Many elements do not easily donate or receive electrons. Instead they share them with another atom. • Covalent bondsare formed when elements share electrons between the elements (this is generally formed between non metals). • Covalently formed compounds are called molecules.
Covalent Bonds • It is easy to distinguish a covalent bond from an ionic bond as in a covalent bond all of the elements bonded are non metals (right of stair step plus hydrogen). • Water is a covalently bonded compound. Two hydrogen atoms and one oxygen atom share their electrons to form a stable configuration for both atoms (8 for Oxygen and 2 for Hydrogen) • Binary covalent bonds never include metals.
Covalent Bonds are in a Tug-of-War • Since the atoms in a covalent bond are not truly giving up their electrons, there is a constant pull on the shared electron between the atoms. • The larger atom has a greater pull and pulls the shared atom closer. • This results in “partial charges” with the larger mass elements taking on a partial negative charge and the smaller mass elements taking on a positive charge.
Polar Molecules • When atoms have a shape that gives them a slightly positive end and a slightly negative end, it is called a polar molecule. • Water (H2O) and ammonia (NH3)are polar molecules. Positive end The bent shape of the molecule gives them positive and negative poles δ+ δ - Negative end
Non Polar Molecules • Some other covalent bonds have a symmetrical shape. • In these situations, electrons are shared equally and a nonpolar moleculeis formed as there are no poles. Carbon dioxide molecule Oxygen molecule No pos. and neg. poles
Diatomic molecules • Many non metals exist naturally in a covalent bond that forms a diatomic molecule. In this situation, two atoms share electrons to become stable. O2 is a common example of a diatomic molecule. Here, two hydrogen atoms become a stable H2 molecule by sharing electrons This diagram shows how two chlorine atoms share electrons to form the diatomic molecule Cl2
Naming Covalent Compounds • Writing the chemical formulas of these compounds is pretty straight forward, but the naming of them can get complicated. • For example N2O, NO, NO2 and N2O5 would all be read as nitrogen oxide under the naming rules for ionic compounds. • However, each of these covalent compounds is distinctly different. Covalent compound naming has one twist.
Greek prefixes • Add the following Greek prefixes to your periodic table (English meaning in parenthesis): • mono (1) hexa (6) • di (2) septa (7) • tri (3) octa (8) • tetra (4) nona (9) • penta (5) deca (10)
Naming covalent compounds includes Greek prefixes for numbers • To solve the naming problem, we turn to Greek prefixes for numbers (now on your periodic table). • In covalent compounds, you have to include the numbers in the subscripts as part of the name. • N2O then becomes dinitrogen oxide • NO then becomes nitrogen monoxide • NO2 then becomes nitrogen dioxide • N2O5 then becomes dinitrogenpentoxide
