Biochemistry___Lesson-2___Chapter 2.5 and 2.6

Question 1

What is the area around the nucleus of an atom that can hold 1 orbit / 2 electrons, or when farther away, 4 orbitals/ 8 electrons?

Answer 1

Electron shell

Question 2

What is the outermost electron shell of an atom, which participates in chemical reactions only when it is not full?

Answer 2

Valence shell

Question 3

What is the general name for an attraction that holds two atoms close together?

Answer 3

Chemical bond

Question 4

What kind of chemical bond forms when an electron is transferred between atoms?

Answer 4

Ionic bond

Question 5

What type of chemical bond forms when electrons are shared between atoms?

Answer 5

Covalent bond

Question 6

What do we call a substance in which the atoms are held together by covalent bonds?

Answer 6

Molecule

Question 7

What is the name of the attraction of an atomic nucleus for electrons?

Answer 7

Electronegativity

Question 8

What type of chemical bond forms when electrons are shared equally between 2 atoms?

Answer 8

Nonpolar covalent bond

Question 9

What type of chemical bond forms when electrons are shared unequally between 2 atoms?

Answer 9

Polar covalent bond

Question 10

Draw a hydrogen atom (H) and label the valence shell.

Answer 10

Question 11

Draw an oxygen atom (O) and label the valence shell.

Answer 11

Question 12

Draw a nitrogen atom (N) and label the valence shell.

Answer 12

Question 13

Draw a carbon atom (C) and label the valence shell.

Answer 13

Question 14

Draw the structural formula and electron distribution diagram of hydrogen gas (H2).

Answer 14

Question 15

Draw the structural formula and electron distribution diagram of oxygen gas (O2).

Answer 15

Question 16

Draw the structural formula and electron distribution diagram of methane (CH4).

Answer 16

Question 17

Draw the structural formula and electron distribution diagram of water (H2O).

Answer 17

Question 18

How many electrons can be held in the first energy shell?

Answer 18

2

Question 19

How many electrons can be held in the second energy shell?

Answer 19

8

Question 20

How many electrons can be held in the third energy shell?

Answer 20

8

Question 21

How many electron shells do atoms in the first row of the periodic table have?

Answer 21

1

Question 22

How many electron shells do atoms in the second row of the periodic table have?

Answer 22

2

Question 23

What directly determines the chemical properties of an atom?

Answer 23

Valence electrons

Question 24

How many covalent bonds can a Hydrogen atom form?

Answer 24

1

Question 25

How many covalent bonds can an Oxygen atom form?

Answer 25

2

Question 26

How many covalent bonds can a Nitrogen atom form?

Answer 26

3

Question 27

How many covalent bonds can a Carbon atom form?

Answer 27

4

Question 28

What is the difference between a polar covalent bond and a nonpolar covalent bond?

Answer 28

Both share electrons, but the polar bond shares them unequally.

Question 29

Explain the formation of a water molecule. Use all these phrases: 2 unpaired valence electrons, 1 unpaired valence electron, sharing, filled valence shell (8 electrons), filled valence shell (2 electrons), covalent bond.

Answer 29

A water molecule (H2O) is formed when an oxygen atom (2 unpaired valence electrons) fills its valence shell by sharing each unpaired electron with the unpaired electron of a hydrogen atom (1 unpaired valence electron). The result is oxygen with a filled valence shell (8 electrons) and 2 hydrogen atoms, each with a filled valence shell (2 electrons). The oxygen atom is sharing a pair of electrons with 2 different hydrogen atoms. The sharing causes the oxygen and hydrogen atoms to stay close together in what is called a covalent bond.

Question 30

Describe the structure of a water molecule. Include partial charges in your drawing. Use all these phrases: covalent bond, not shared equally, electronegativity, polar covalent bond, slightly negative, slightly positive.

Answer 30

Oxygen forms 2 covalent bonds with 2 different hydrogen atoms. The electrons in the covalent bonds are not shared equally because oxygen has a greater electronegativity compared to hydrogen. The shared electrons in each covalent bond are thus closer to oxygen, forming a polar covalent bond. Because the electrons (which are negative) are closer to oxygen, the oxygen has a slightly negative charge, and the hydrogens have a slightly positive charge.