MasteringBiology Chapter 2 Homework
An atom has 8 protons, 8 neutrons, and 8 electrons. Another isotope of the same element might have ...
10 neutrons.
The innermost electron shell of an atom can hold up to _____ electrons.
2
Choose the correct balanced equation for the following reaction. C8H18 + O2 → CO2 + H2O
2 C8H18 + 25 O2 → 16 CO2 + 18 H2O
To fill the valence shell, an electrically neutral, unbonded atom with atomic number 8 must add ...
2 electrons.
What is the mass number of an ion with 109 electrons, 159 neutrons, and a +1 charge?
269
An atom's atomic number is 7. Its valence is most likely ...
3
The mass number of an atom is 15, and its atomic number is 7. The atom probably has...
8 neutrons in the nucleus.
What happens when two atoms form a chemical bond?
A chemical bond forms when two atoms transfer or share outer electrons to complete their outer shells.
Which statement about relative potential energy of electrons is correct?
An electron in the 3 p orbital of the third electron shell has more potential energy than an electron in the 2 p orbital of the second electron shell.
What does the term electron orbital describe?
An electron orbital describes a three-dimensional space where an electron can be found 90% of the time.
Which statement about the following reaction is true? 4 Fe + 3 O2 → 2 Fe2O3
Four atoms of Fe react with 3 molecules of O2 to form 2 molecules of Fe2O3
Which statement is true of the relation between life and chemical equilibrium?
Living cells avoid chemical equilibrium by taking in energy and materials. The only way to avoid equilibrium is to exchange materials and energy with the environment.
Which of the following is a trace element required by most living organisms?
Magnesium
Which of the following is true of activation energy?
Molecules usually get it from thermal energy.
Which answer correctly ranks the atoms in terms of decreasing electronegativity (the highest electronegativity first)?
O, N, C, H
Use your knowledge of electronegativity to pick out the most polar bond in the list below.
O-H because they are on opposite ends of the electronegativity scale
What model most accurately represent the current view of the structure of an atom? Probability or planetary model?
Probability model.
Which of the following subatomic particles always has a positive charge?
Proton
Dr. Haxton says the O-O bond is polar and the C-C bond is nonpolar. A good student would say ...
Wrong again, Ralph. Both bonds are non polar. When two atoms of the same kind form a covalent bond, they share electrons equally because their electronegativity is the same.
Can rotations occurs around single bonds?
Yes
Atoms with the same number of protons but with different electrical charges _____.
are different ions
An ionic bond is formed when _____.
one atom transfers an electron to another atom
Changing the number of _____ would change an atom into an atom of a different element.
protons in an atom
Compared to covalent bonds, ionic bonds ...
rely much less on electron-sharing.
What type of bond joins the carbon atom to each of the hydrogen atoms?
single (nonpolar) covalent
The atoms of different phosphorus isotopes _____.
have different numbers of neutrons
Fluorine's atomic number is 9 and its atomic mass is 19. How many neutrons does fluorine have?
10
Under standard conditions the reversible reaction A + B → C + D has a ΔG∘ = -25 kJ/mol. What is ΔG when: T = 475 K, [A] = 0.5M, [B] = 0.2 M, [C] = 0.2 M, and [D] = 0.3 M?
-27 kJ/mol The nonstandard concentrations have lowered ΔG by 2 kJ.mol.
An electrically neutral molecule has the formula C3H4O2N. If the carbon atoms form the usual number of bonds, how many covalent bonds will each hydrogen atom have with other atoms in the molecule?
1
In molecules, C, H, O, and N atoms usually make __, __, __, and __ bonds respectively.
4, 1, 2, 3
An uncharged atom of boron has an atomic number of 5 and an atomic mass of 11. How many protons does boron have?
5
What is the atomic number of an atom that has 6 protons, 6 neutrons, and 6 electrons?
6
A positive ion with two units of charge has 10 neutrons and 8 protons. The ion also has ...
6 electrons.
Two C atoms form a double bond. Each C is bound to two H atoms. Which statement is true?
All the atoms lie in a plane because the double bond limits all the atoms.
Choose the appropriate balanced equation for the following chemical reaction. C6H6 + H2 → C6H12
C6H6 + 3 H2 → C6H12
An atom has 6 electrons, 6 protons, and 6 neutrons. You can tell that this atom belongs to the element _____ because _____________________.
C; it has 6 protons.
Which fact is most important in explaining how molecules convert thermal energy to activation energy (EA)?
Distortion increases a molecule's potential energy. In a collision, kinetic energy becomes the potential energy of distortion, which can weaken bonds enough to permit a reaction.
What type of bond shares two pairs of electrons?
Double covalent
What determines the atom's size?
Electrons
If you want a molecule that is highly polar, look for one that contains:
H-N because they differ most in electronegativity
Which of the following are compounds?
H2O and CH4, but not O2
What name is given to the bond between water molecules?
Hydrogen
In salt, what is the nature of the bond between sodium and chlorine?
Ionic
Which statement is true of the transition state?
It can break apart to yield either reactants or products and it is extremely unstable and lasts only an instant.
By making two covalent bonds, an O atom (with 8 protons) fills its valence shell. Why does the atom's charge stay close to zero?
Shared electrons aren't always near oxygen.
Dr. Haxton says he has found a reaction that is truly irreversible. What would a good student say?
Sorry, Doctor. All reactions are reversible.
Which statement is true of all atoms that are anions?
The atom has more electrons than protons.
What determines the types of chemical reactions that an atom participates in?
The number of electrons in the outermost electron shell
What relationships is true of an uncharged atom?
The number of protons is equal to the number of electrons.
A chemist calculates that a certain reaction would result in ΔH = -9 kJ and TΔS = +1 kJ. What can you conclude?
The reaction will occur spontaneously, because it decreases G. ΔG = ΔH - TΔS = -9 kJ - (+1 kJ) = -10 kJ. Since the free energy decreases, the reaction will run spontaneously.
What shell has a highest energy?
The valence shell
Which answer helps to explain why carbon atoms tend to make 4 covalent bonds?
The valence shell needs 8 electrons.
Which of these refers to atoms with the same atomic number but different atomic masses?
These atoms are isotopes.
True or false: Ions may form by transferring an atomic nucleus (with or without electrons) to another molecule.
True For example, a hydrogen nucleus (H+) may move between two water molecules, making an H3O+ ion and an OH- ion.
What bond can form between atoms of equal electronegativity?
Van der Waals interactions can form between atoms of equal electronegativity.
Which statement about weak bonds is correct?
Weak bonds are transient and easily reversible.
Partial charges occur when ...
a covalent bond links atoms of two kinds and atoms share electrons unequally.
Radioactive decay is likely to occur when ...
an atom has too many neutrons. The atomic nucleus because unstable if the ration of protons to neutrons is too far from unity
An ionic bond involves _____.
an attraction between ions of opposite charge
Potential energy is always ...
associated with position or arrangement.
In a double covalent bond, a carbon atom shares ...
electrons in two orbitals.
A substance that cannot be broken down into other substances by ordinary chemical procedures is a(n) _____.
element
Covalent bonds hold atoms together because they ...
fill shells without giving atoms much charge and bring electrons closer to protons.
Catalysts speed reactions mainly by ...
lowering EA. Catalysts always lower EA, though they may have other effects as well. With a lower EA, a larger fraction of collisions can produce the transition state.
A(n) _____ refers to two or more atoms held together by covalent bonds.
molecule
The reactivity of an atom arises from _________.
the existence of unpaired electrons in the valence shell
Dr. Jones says an atom has 3 electrons in the first shell and four electrons in the second shell. Someone should tell Dr. Jones that ...
the first shell shouldn't have 3 electrons.
Chemical equilibrium is reached when _____.
the forward and reverse reactions occur at the same rate so that the concentrations of reactants and products remain the same
For the reaction ATP + H2O → ADP + Pi, the change in standard free energy (ΔG∘) is -30.5 kJ/mol. From this information we can conclude that ...
the forward reaction will be spontaneous under standard conditions because ΔG is less than zero.
Knowing the atomic mass of an element allows inferences about which of the following?
the number of protons plus neutrons in the element
Two atoms always represent the same element if they have ...
the same number of protons
Hydrogen bonding is most often seen _____.
when hydrogen is covalently bonded to an electronegative atom
In the equation ΔG = ΔH - TΔS, the change in the amount of disorder in the system is symbolized by ...
ΔS S is entropy
