Chap 2
Copper has an atomic number of 29 and a mass number of 64. What would result if an uncharged copper atom lost two electrons?
The atomic number would remain 29, the mass number would remain 64, and the atom would be a cation with a +2 charge.
A particular carbon isotope has an atomic number of 6 and an atomic mass of 14. The respective number of neutrons, protons, and electrons that this carbon isotope has is
The atomic number, 6, is equal to the number of protons. Therefore, the number of electrons in an electrically neutral atom would also be 6. The number of neutrons must be 8 because the atomic mass is 14 (14 - 6 = 8).
What does the fullness of the valence shell determine?
The fullness of the valence shell determines the pattern of covalent bonding or ionization. The reactivity of an atom is a function of the presence of unpaired electrons in one or more orbitals of their valence shells.
What name is given to the bond between water molecules?
hydrogen A hydrogen atom with a net positive charge is attracted to an oxygen atom with a net negative charge
Which of the following is broken when water evaporates?
hydrogen bonds
What are the four most abundant elements found in living systems?
hydrogen, oxygen, nitrogen, and carbon They make up 96% of living matter
A hydrogen bond
is a weak chemical bond
When the proton number and electron number are unequal, the atom or molecule
is an ion When the proton number and electron number are unequal, the atom or molecule has a net positive charge (cation) or a net negative charge (anion).
Which of the following is a trace element required by most living organisms?
manganese
Which molecule has the shape of a completed tetrahedron? (
methane (CH4)
A(n) _____ refers to two or more atoms held together by covalent bonds.
molecule
A carbon atom and a hydrogen atom form what type of bond in a molecule?
nonpolar covalent bond
Bonds between two atoms that are equally electronegative are
nonpolar covalent bonds
The chemical characteristics or reactivity of an element depend mostly on the
number of electrons in its outermost shell
Which of these relationships is true of an uncharged atom?
The number of protons is equal to the number of electrons In this situation the number of positive charges is equal to the number of negative charges.
Which statement describes a reversible reaction that has reached chemical equilibrium?
The rate of the reverse reaction equals the rate of the forward reaction.
Which of these refers to atoms with the same atomic number but different atomic masses?
These atoms are isotopes. Atoms with the same atomic number and different atomic masses are referred to as isotopes
Which statement is true about chemical reactions? (
They involve the making and breaking of chemical bonds.
The innermost electron shell of an atom can hold up to _____ electrons
Two
An uncharged atom of boron has an atomic number of 5 and an atomic mass of 11. How many protons does boron have?
5 The atomic number is equal to the number of protons.
How many electrons would be present in the valence shell of a sulfur atom (atomic number 16, mass number 32)?
6
What is the atomic number of an atom that has 6 protons, 6 neutrons, and 6 electrons?
6 This is an atom of carbon, an element with 6 protons. Atomic number is the number of protons in an atom.
A neutral atom of chlorine has an atomic number of 17. It has __________ electrons in its third shell
7
An element has eight protons, nine neutrons, and eight electrons. Its atomic number and atomic mass, respectively, are
8 and 17
There are __________ naturally occurring elements
92
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.
The compound CaSO4 ionizes into a calcium ion and a sulfate ion (SO4). Calcium has two electrons in its outer shell. Upon ionization, what would you expect the charge on the sulfate ion to be?
-2 By gaining two electrons from calcium, the sulfate ion now has a charge of -2 and calcium has a charge of +2.
Fluorine's atomic number is 9 and its atomic mass is 19. How many neutrons does fluorine have?
10 Atomic mass is equal to the number of protons plus the number of neutrons (19-9 = 10)
What is the maximum number of covalent bonds that an oxygen atom with atomic number 8 can make with hydrogen?
2
What is generally true about essential elements and living organisms?
Although all forms of life require iron, other elements are required only by certain species.
What is the role of van der Waals interactions in biological molecules?
Although they are weak bonds, van der Waals interactions help to reinforce the three-dimensional shapes of large molecules.
Which of the following is a trace element?
Copper
What is the difference between covalent bonds and ionic bonds?
Covalent bonds involve the sharing of electrons between atoms; ionic bonds involve the electrical attraction between charged atoms.
Which of the following has negligible mass?
Electron
A substance that cannot be broken down into other substances by ordinary chemical procedures is a
Element
How would you respond to this reasoning: oxygen is not a greenhouse gas; therefore, gases containing oxygen—such as ozone, nitrous oxide, and carbon dioxide—are not greenhouse gases either.
False. Compounds can have emergent properties that are very different from those of the elements that form them.
If you were told that concentrations of trace elements above what is required by organisms generally have no effect on those organisms, what would you say?
False. Elevated concentrations of some trace elements such as cobalt and chromium can be toxic. Although considered essential to life at minute amounts, high concentrations of trace elements (such as heavy metals) in the environment can lead to disease and mortality among organisms.
In salt, what is the nature of the bond between sodium and chlorine?
Ionic Sodium and chlorine ions are attracted to each other
What is the mass number of an ion with 104 electrons, 158 neutrons, and a +1 charge?
Mass Number = Protons + Neutrons A +1 charge means the protons exceed the electrons by one.
Which of the following subatomic particles has appreciable mass but no charge?
Neutron
Which of the following bonds can form between atoms of equal electronegativity?
Van der Waals interactions can form between atoms of equal electronegativity Even nonpolar covalent bonds have temporary regions of partial positive and negative charge, due to the chance movements of electrons. Attractions between such transient positive and negative charges create weak Van der Waals interactions.
When one or more pairs of valence electrons are shared by two neutral atoms, what type of bond is formed?
a covalent bond Covalent bonds are formed between atoms that share one or more pairs of valence electrons.
The most common form of calcium has 20 protons, 20 neutrons, and 20 electrons. Which of the following elements would be an isotope of calcium?
an atom with 20 protons, 21 neutrons, and 20 electrons
An ionic bond involves
an attraction between ions of opposite charge
Atoms with the same number of protons but with different electrical charges
are different ions Ions are charged atoms.
In which of the following will isotopes of an element always differ?
atomic mass Atomic mass refers to the number of protons and neutrons in an atom. Atomic forms of an element with the same number of protons (atomic number) but different numbers of neutrons are isotopes of that element.
Ionic bonds form as a result of __________
attraction between ions that have opposite charges
Why are radioactive isotopes useful in scientific research?
because they can be used as tracers to follow particular atoms and molecules through metabolic pathways
About 25 of the 92 natural elements are known to be essential to life. Which 4 of these 25 elements make up approximately 96% of living matter?
carbon, hydrogen, nitrogen, oxygen
A(n) ________ has charge but negligible mass, whereas a(n) ________ has mass but no charge
electron; neutron
The number of protons in an uncharged atom
equals the number of electrons; An uncharged atom has an equal number of protons and electrons.
The atoms of different phosphorus isotopes
have different numbers of neutrons The phosphorus atom is defined by its proton number. Changes in neutron number alter the mass of the atom, but not its chemical behavior or reactivity
Phosphorus-32 (radioactive) has __________ than phosphorus-35 (normal)
he numbers 32 and 35 refer to mass number (number of protons plus neutrons). All the atoms of the same element have the same number of protons, but different isotopes of the same element have different numbers of neutrons. Because 35 - 32 = 3, P-32 has three fewer neutrons than P-35.
Some groups of chemical elements react similarly to one another. For example, the chemistries of sodium and of lithium are similar, as are the chemistries of chlorine and of iodine. These similarities in chemistry result when different elements have similar
numbers of outer-shell electrons
An ionic bond is formed when
one atom transfers an electron to another atom Transfer of an electron from one atom to another results in a positive ion (cation) and a negative ion (anion), which usually attract each other to form an ionic bond. However, the ions need not have acquired their electrical charge due to an electron transfer with each other.
A covalent bond is likely to be polar when
one of the atoms sharing electrons is more electronegative than the other atom
A covalent bond is likely to be polar if
one of the atoms sharing electrons is much more electronegative than the other
Changing the number of _____ would change an atom into an atom of a different element
protons in an atom Atoms of each element have a unique number of protons within their nuclei. Changing the number of protons in an atom occurs only in nuclear reactions, not chemical reactions
An uncharged atom of nitrogen (atomic number = 7) has
seven protons and seven electrons
What type of bond joins the carbon atom to each of the hydrogen atoms?
single (nonpolar) covalent Each carbon-hydrogen bond involves a single pair of equally shared electrons.
Pharmaceutical researchers are often interested in blocking particular receptor proteins on cell surfaces. What chemical property of a molecule would be most important for this type of application?
the molecules shape
What determines the types of chemical reactions that an atom participates in?
the number of electrons in the outermost electron shell \ An atom is least likely to participate in a reaction when its outermost shell is stable.
Atomic number equals
the number of protons
The type of bonding and the numbers of covalent bonds an atom can form with other atoms is determined by
the number of unpaired electrons in the valence shell
Hydrogen bonding is most often seen
when hydrogen is covalently bonded to an electronegative atom Highly electronegative atoms attract shared electrons more strongly than hydrogen does, resulting in a slight positive charge on the hydrogen atom. The slightly positive hydrogen atom is then attracted to another electronegative atom, forming a hydrogen bond.
When do hydrogen bonds occur?
when partial opposite charges on molecules come close enough to attract each other when partial opposite charges on molecules come close enough to attract each other
For most atoms, when is an unreactive configuration of electrons attained?
when the atom has eight electrons in its outermost shell
