{"id":73,"date":"2022-02-07T21:13:52","date_gmt":"2022-02-08T02:13:52","guid":{"rendered":"https:\/\/pressbooks.bccampus.ca\/biology1190chemistry\/?post_type=chapter&p=73"},"modified":"2025-06-03T19:11:31","modified_gmt":"2025-06-03T23:11:31","slug":"covalent-bonds","status":"publish","type":"chapter","link":"https:\/\/pressbooks.bccampus.ca\/biology1190chemistry\/chapter\/covalent-bonds\/","title":{"raw":"Covalent bonds","rendered":"Covalent bonds"},"content":{"raw":"Atoms with similar electronegativities will not transfer electrons to form an ionic bond between one another. Instead, they may share <\/strong>electrons to form a covalent bond<\/strong>. For example, carbon (C) has an atomic number of 6 and hydrogen (H) has an atomic number of 1. The valence shell of C is the second shell and it is half-full<\/em>. The valence shell of H is the first shell and it is also half-full<\/em>. Therefore, these atoms have similar electronegativities<\/strong>. When they come into proximity of one another, the valence electrons of C will complete the valence of H atoms and vice versa. Because these atoms pull on the shared electrons with equal force<\/em>, the bonds between C and H are nonpolar covalent bonds<\/strong>. The electrons are shared equally between the bonding partners.\r\n\r\n<\/a>In contrast, oxygen (O) has an atomic number of 8 and its valence shell is the second shell. O is much closer to filling its valence shell than H; therefore, O is more electronegative than H<\/strong>. O and H can react to form water (H2<\/sub>O). In water, O and H will share <\/em>their valence electrons to fill each other\u2019s valence shells. However, because O pulls on electrons with more force, the shared electrons tend to reside with O more often than with either H atom. That means that O carries a partial negative charge (\u03b4<\/strong>-) <\/strong>and C carries a partial positive charge<\/strong> (\u03b4<\/strong>+)<\/strong>, resulting in a polar covalent bond<\/strong> between the atoms. Covalent bonds are relatively strong bonds as compared to electrostatic interactions such as ionic or hydrogen bonds.\r\n\r\n \r\n
Activity:<\/strong> Drag and drop the correct type of covalent bonds that form methane (left) and water (right).<\/div>\r\n[h5p id=\"67\"]\r\n
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IMPORTANT<\/strong>: Molecules and compounds are not the same thing!<\/p>\r\n

The atoms in molecules are joined by covalent bonds<\/strong>. Compounds contain two different atoms joined by either covalent or ionic bonds. Molecular oxygen (O2<\/sub>) is a molecule containing two of the same atoms joined by nonpolar covalent bonds<\/strong>. However, O2<\/sub> is not a compound because it contains only one type of atom. Water (H2<\/sub>O) is both a molecule and a compound because the atoms in water are joined by covalent bonds and it contains two different atoms: O and H.<\/p>\r\n\r\n<\/div>\r\n \r\n

Activity:<\/strong> Read the statements below and decide whether the statements are true or false.<\/div>\r\n[h5p id=\"55\"]\r\n[h5p id=\"56\"]\r\n
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Chemistry in the clinic:<\/p>\r\n

The polarity<\/strong> of a molecule is determined by the polarity of the covalent bonds within the molecule as well as the way the bonds are arranged. For example, carbon dioxide <\/strong>(CO2<\/sub>) is a nonpolar molecule<\/strong>, despite containing two atoms with very different electronegativities. In CO2<\/sub>, carbon forms two double bonds to each of the two oxygen atoms. Because the electron pairs strongly repel one another, CO2<\/sub> takes on a linear shape (Figure 8). The two oxygens face away from one another symmetrically, effectively cancelling the polarity of the C-O bonds<\/em>. For this reason, CO2<\/sub> is poorly soluble in aqueous solutions such as blood plasma. You will learn in a future lecture on blood that CO2<\/sub> must be converted into a soluble compound called carbonic acid (H2<\/sub>CO3<\/sub>) by the action of an enzyme called carbonic anhydrase<\/strong> in red blood cells.<\/p>\r\n\r\n<\/div>\r\n \r\n\r\n[caption id=\"attachment_481\" align=\"aligncenter\" width=\"620\"]\"Figure Figure 8. Carbon dioxide is a linear, nonpolar molecule[\/caption]","rendered":"

Atoms with similar electronegativities will not transfer electrons to form an ionic bond between one another. Instead, they may share <\/strong>electrons to form a covalent bond<\/strong>. For example, carbon (C) has an atomic number of 6 and hydrogen (H) has an atomic number of 1. The valence shell of C is the second shell and it is half-full<\/em>. The valence shell of H is the first shell and it is also half-full<\/em>. Therefore, these atoms have similar electronegativities<\/strong>. When they come into proximity of one another, the valence electrons of C will complete the valence of H atoms and vice versa. Because these atoms pull on the shared electrons with equal force<\/em>, the bonds between C and H are nonpolar covalent bonds<\/strong>. The electrons are shared equally between the bonding partners.<\/p>\n

<\/a>In contrast, oxygen (O) has an atomic number of 8 and its valence shell is the second shell. O is much closer to filling its valence shell than H; therefore, O is more electronegative than H<\/strong>. O and H can react to form water (H2<\/sub>O). In water, O and H will share <\/em>their valence electrons to fill each other\u2019s valence shells. However, because O pulls on electrons with more force, the shared electrons tend to reside with O more often than with either H atom. That means that O carries a partial negative charge (\u03b4<\/strong>-) <\/strong>and C carries a partial positive charge<\/strong> (\u03b4<\/strong>+)<\/strong>, resulting in a polar covalent bond<\/strong> between the atoms. Covalent bonds are relatively strong bonds as compared to electrostatic interactions such as ionic or hydrogen bonds.<\/p>\n

 <\/p>\n

Activity:<\/strong> Drag and drop the correct type of covalent bonds that form methane (left) and water (right).<\/div>\n
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