6.2 Covalent Bonding Plants absorb water through their roots from soil or from a solution containing nutrients. Carbon dioxide from the air enters the plants through small openings in their leaves. The plants use the energy from sunlight to convert water and carbon dioxide into a sugar.

6.2 Covalent Bonding Covalent Bonds covalent bond - chemical bond in which two atoms share a pair of valence electrons - attraction between the shared electrons and protons in nucleus hold the atoms together Notes

6.2 Covalent Bonding There are several ways to show a covalent bond. In the electron dot model bond is shown by a pair of dots in the space between the symbols for the hydrogen atoms. In the structural formula, pair of dots is replaced by a line. The electron cloud and the space-filling models show that orbitals of atoms overlap when a covalent bond forms. Covalent Bonds Notes

6.2 Covalent Bonding This illustration shows four ways to represent a covalent bond between two hydrogen atoms. As a space shuttle lifts off, it leaves a water vapor trail. A reaction of hydrogen and oxygen produces the water. Covalent Bonds

6.2 Covalent Bonding Water H O Each hydrogen has 1 valence electron Each hydrogen wants 1 more The oxygen has 6 valence electrons The oxygen wants 2 more They share to make each other happy

6.2 Covalent Bonding Water Put the pieces together H O H

6.2 Covalent Bonding Water Put the pieces together The first hydrogen is happy The oxygen still wants one more H O H

6.2 Covalent Bonding Water The second hydrogen attaches Every atom has full energy levels H O H

6.2 Covalent Bonding

Many nonmetal elements exist as diatomic molecules. Diatomic means “two atoms.” Covalent Bonds

6.2 Covalent Bonding Covalent bonding Fluorine has seven valence electrons F A second atom also has seven F By sharing electrons …both end with full orbitals 8 Valence electrons 8 Valence electrons

6.2 Covalent Bonding What happens when atoms don’t share electrons equally? Unequal Sharing of Electrons What factors determine whether a molecule is polar?

6.2 Covalent Bonding When atoms form a polar covalent bond, the atom with the greater attraction for electrons has a partial negative charge. The other atom has a partial positive charge. Unequal Sharing of Electrons The type of atoms in a molecule and its shape are factors that determine whether a molecule is polar or nonpolar.

6.2 Covalent Bonding “Like dissolves like” –Polar will dissolve polar –Non-polar will dissolve non-polar Water – polar Oil – non-polar Notes

6.2 Covalent Bonding Polar Covalent Bonds - In a molecule of an element, -atoms that form covalent bonds have the same ability to attract an electron. -Shared electrons are attracted equally to the nuclei of both atoms. - In a molecule of a compound - electrons may not be shared unequally Unequal Sharing of Electrons Notes

6.2 Covalent Bonding A covalent compound forms when hydrogen reacts with chlorine. A chlorine atom has a greater attraction for electrons than a hydrogen atom does. In a hydrogen chloride molecule, the shared electrons spend more time near the chlorine atom than near the hydrogen atom. Unequal Sharing of Electrons Notes polar covalent bond - A covalent bond in which electrons are not shared equally

6.2 Covalent Bonding Shared electrons in a hydrogen chloride molecule spend less time near the hydrogen atom than near the chlorine atom. Unequal Sharing of Electrons

6.2 Covalent Bonding Polar and Nonpolar Molecules Can you assume that a molecule that contains a polar covalent bond is polar? When a molecule has only two atoms, it will be polar. When molecules have more than two atoms, the answer is not obvious. Unequal Sharing of Electrons

6.2 Covalent Bonding In a carbon dioxide (CO 2 ) molecule, the polar bonds between the carbon atom and the oxygen atoms cancel out because the molecule is linear. Unequal Sharing of Electrons

6.2 Covalent Bonding In a carbon dioxide (CO 2 ) molecule, the polar bonds between the carbon atom and the oxygen atoms cancel out because the molecule is linear. In a water (H 2 O) molecule, the polar bonds between the oxygen atom and the hydrogen atoms do not cancel out because the molecule is bent. Unequal Sharing of Electrons

6.2 Covalent Bonding In a molecular compound, there are forces of attraction between molecules. These attractions are not as strong chemical bonds, but they are strong enough to hold molecules together in a liquid or solid. Water molecules are similar in mass to methane (CH 4 ) molecules. Yet, methane boils at –161.5°C, and water boils at 100°C, because methane molecules are nonpolar and water molecules are polar. Attraction Between Molecules

6.2 Covalent Bonding Dashed lines represent attractions between partially positive hydrogen atoms and partially negative oxygen atoms. The symbols  – and  + are used to indicate a partial charge. Attraction Between Molecules

6.2 Covalent Bonding Attractions among nonpolar molecules are weaker than attractions among polar molecules, but they do exist. Attractions among nonpolar molecules explain why carbon dioxide can exist as dry ice and why nitrogen can be stored as a liquid at low temperatures and high pressures. Attraction Between Molecules

6.2 Covalent Bonding Assessment Questions 1.What attractions hold two atoms in a molecule together? a.attraction between ions with opposite charges b.attraction between the nuclei of the atoms and shared electrons c.attraction between each nucleus and the electrons of the other atom d.attraction between the molecule and other molecules

6.2 Covalent Bonding Assessment Questions 1.What attractions hold two atoms in a molecule together? a.attraction between ions with opposite charges b.attraction between the nuclei of the atoms and shared electrons c.attraction between each nucleus and the electrons of the other atom d.attraction between the molecule and other molecules ANS:B

6.2 Covalent Bonding Assessment Questions 2.What determines whether a molecule is polar? a.type of atoms and shape of molecule b.mass of atoms and number of valence electrons c.type and mass of atoms d.ionization energy and number of covalent bonds

6.2 Covalent Bonding Assessment Questions 2.What determines whether a molecule is polar? a.type of atoms and shape of molecule b.mass of atoms and number of valence electrons c.type and mass of atoms d.ionization energy and number of covalent bonds ANS:A

6.2 Covalent Bonding Assessment Questions 3.Why does water have a much higher boiling point than methane? a.Methane molecules are more polar, so its molecules have stronger attractive forces. b.Partial charges on the polar water molecules increase attractive forces between molecules. c.A water molecule has much more mass than a methane molecule, so water has a higher boiling point. d.Water has a higher boiling point because its molecules do not contain carbon atoms.

6.2 Covalent Bonding Assessment Questions 3.Why does water have a much higher boiling point than methane? a.Methane molecules are more polar, so its molecules have stronger attractive forces. b.Partial charges on the polar water molecules increase attractive forces between molecules. c.A water molecule has much more mass than a methane molecule, so water has a higher boiling point. d.Water has a higher boiling point because its molecules do not contain carbon atoms. ANS:B