Chapter 2 Flashcards
(17 cards)
Which of the following is false?
a. An element is defined by its atomic number.
b. Ninety-two elements occur naturally.
c. An atom consists of subatomic particles.
d. Electron shells increase in energy closer to the nucleus.
d
The mass number of an element is equal to
a. the mass of its atom’s protons and neutrons.
b. the mass of its atom’s neutrons.
c. the mass of its atom’s protons.
d. its atomic number.
a
Isotopes are defined as
a. atoms of the same element with different numbers of protons.
b. radioactive elements.
c. stable elements.
d. atoms of the same element with different numbers of neutrons
d
Molecules
a. always consist of different elements bonded together.
b. may be polar or nonpolar.
c. may be held together entirely by hydrogen bonds.
d. cannot be held together by ionic bonds.
b
Covalent bonds
a. link water molecules in ice.
b. create only nonpolar molecules.
c. bind sodium and chlorine in table salt.
d. link hydrogen to oxygen in a water molecule.
d
An atom consists of an atomic nucleus composed of positively charged________and uncharged_________. Orbiting around the nucleus are________ that occupy discrete spaces called______.
protons, neutrons, electrons and electron shells
An atom that has lost or gained one or more electrons is called a(n)_______. If an atom loses an electron, it takes on a(n)________charge. Atoms with opposite charges attract one another, forming_______ bonds.
ion, positive and ionic
Atoms of the same element that differ in the number of neutrons in their nuclei are called_____. Some of these atoms spontaneously break apart, and in this process, they sometimes become different_________. Atoms that behave this way are described as being_______. .
isotopes, elements and radioactive
An atom with an outermost electron shell that is either completely full or empty is described as_______. Atoms with partially full outer electron shells are_________. Covalent bonds are formed when atoms________electrons, filling their outer shells.
inert, reactive and share
Water is described as______because each water molecule has slightly negative and positive poles. This property allows water molecules to form________bonds with one another. The bonds between water molecules give water_________that produces surface tension.
polar, hydrogen and cohesion
Based on Table 2-1, how many neutrons are there in oxygen? In hydrogen? In nitrogen?
There are eight neutrons in oxygen, zero in hydrogen, and seven in nitrogen.
Distinguish between atoms and molecules and among protons, neutrons, and electrons.
An atom is the smallest particle of an element that still retains the properties of that element. A molecule consists of two or more atoms chemically bonded together. Protons are positively charged subatomic particles found in the atomic nucleus. Neutrons are uncharged subatomic particles found in the atomic nucleus. Electrons are negatively charged subatomic particles found in electron shells around the atomic nucleus.
Compare and contrast covalent bonds and ionic bonds.
Covalent bonds involve the sharing of a pair of electrons between two atoms. Ions form when one or more electrons are transferred between atoms, and ionic bonds result from electrical charge attraction between ions.
Explain how polar covalent bonds allow hydrogen bonds to form, and provide an example.
Polar covalent bonds involve unequal sharing of electrons between two atoms. This produces slight opposite charges on different parts (poles) of the molecule, with one pole being slightly positive and the other slightly negative. Hydrogen bonds form as a result of the attraction between these small opposite charges on polar molecules. For example, water molecules form hydrogen bonds with one another between their slightly positive hydrogen poles and slightly negative oxygen poles.
Why can water absorb a great amount of heat with little increase in its temperature? What is this property called?
Because water molecules are linked by hydrogen bonds, the molecules can move faster only if the hydrogen bonds are broken more often and more rapidly. Breaking hydrogen bonds uses up a considerable amount of heat energy, which is then not available to raise the water’s temperature. This property of water is described as a high specific heat.
Describe how water dissolves a salt.
Because water is polar, the negative poles of water molecules are attracted to the sodium ions and the positive poles to the chloride ions of salt. This attraction to water breaks the ionic bonds that hold salt crystals together. As water molecules surround each ion in salt, the salt dissolves.
Define pH scale, acid, base, and buffer. How do buffers reduce changes in pH when hydrogen ions or hydroxide ions are added to a solution? Why is this phenomenon important in organisms?
The pH scale is a range of values from 0 to 14 that defines the concentration of H+ in a solution and thus how acidic or basic the solution is. The pH number is the negative log of the H+ concentration. An acid is a substance that gives off H+ in solution. A base is a substance that combines with H+ in solution. Buffers are molecules that maintain a solution at a nearly constant pH by accepting or releasing H+ in response to small changes in H+ concentration. Buffers are important in organisms because biological molecules function only within a narrow pH range, and buffers help maintain body fluids within this range.
