2.2 Molecules and Chemical Bonds

Question 1

What are molecules?

Answer 1

groups of two or more atoms attached together that act as a single unit

Question 2

What is a chemical bond?

Answer 2

any form of attraction between atoms that hold them together

Question 3

What is the ability of atoms to combine with other atoms determined by?

Answer 3

largely in part by the electrons farthest from the nucleus, those in the outermost orbitals of the atom

Question 4

What are valence electrons?

Answer 4

electrons in the outermost shell of an atom, they are at the highest energy level of the atom

Question 5

What is a covalent bond?

Answer 5

results when two atoms share electrons

*figure 2.5 textbook

Question 6

What is a molecular orbital?

Answer 6

a merged orbital formed when the outermost orbitals of two atoms come into proximity to each other and two atomic orbitals each containing one electron merge into a single orbital

Question 7

What is a double bond?

Answer 7

two adjacent atoms sharing two pairs of electrons

four orbitals (each occupied by a single electron) merge to form two molecular orbitals

Question 8

When do molecules tend to be most stable?

Answer 8

when the two atoms forming a bond share enough electrons to completely occupy the outermost energy level or shell

Question 9

What is a polar covalent bond?

Answer 9

the resulting interaction when electrons are shared unequally between the two atoms

*figure 2.7 textbook

Question 10

What does the unequal sharing of electrons result from?

Answer 10

a difference in the ability of the atoms to attract electrons aka electronegativity

Question 11

What is electronegativity?

Answer 11

the ability of atoms to attract electrons

Question 12

Describe the trend of electronegativity across a row in the periodic table.

Answer 12

• tends to increase across a row in the periodic table
• as the number of positively charged protons across a row increases, negatively charged electrons are held more tightly to the nucleus

ie. therefore oxygen is more electronegative than hydrogen and attracts electrons more readily than hydrogen

Question 13

What is a nonpolar covalent bond?

Answer 13

a covalent bond between atoms that have the same, or nearly the same, electronegativity

the atoms share the bonding electron pair almost equally

Question 14

Why are molecules held together by nonpolar covalent bonds important in cells?

Answer 14

they do not mix well with water

Question 15

Describe an ionic bond.

Answer 15

forms between oppositely charged ions

• when an atom of very high electronegativity is paired with an atom of very low electronegativity, the difference in electronegativity is so great that the electronegative atom “steals” the electron from its less electronegative partner
• atom with the extra electron has a negative charge and is a negative ion
• atom that has lost an electron has a positive charge and is a positive ion

*figure 2.8 textbook

Question 16

What happens when sodium chloride is placed in water?

Answer 16

the salt dissolves to form sodium ions that have lost an electron and so are positively charged, and chloride ions that have gained an electron and so are negatively charged

Question 17

What happens when sodium chloride is in solution?

Answer 17

the two ions are pulled apart and become surrounded by water molecules

• negatively charged ends of water molecules are attracted to the positively charged sodium ion, and the positively charged ends of other water molecules are attracted to the negatively charged chloride ion
• only as water evaporates do the concentrations of Na+ and Cl- increase to the point where the ions join and precipitate as salt crystals

*figure 2.8 textbook

Question 18

What is a chemical reaction?

Answer 18

process by which atoms or molecules called reactants, are transformed into different molecules called products

Question 19

What can change in a chemical reaction?

Answer 19

chemical bonds that link atoms in molecules

Question 20

What happens during a chemical reaction?

Answer 20

atoms keep their identity but change which atoms they are bonded to (bonds are broken and new bonds are formed)

*figure 2.9 textbook

Question 21

What do chemical reactions do in biological systems?

Answer 21

chemical reactions provide a way to build and break down molecules for use by the cell, as well as to harness energy, which can be held in chemical bonds