Book: Ch. 2

Question 1

Define an element.

Answer 1

An element is the simplest type of matter with unique physical and chemical properties. It consists of only one kind of atom and, therefore, cannot be broken down into a simpler type of matter by any physical or chemical methods.

Question 2

Several elements occur in molecular form (which means…): _____

Answer 2

a molecule is an independent structure of two or more atoms bound together (Figure 2.1B). Oxygen, for example, occurs in air as diatomic (two-atom) molecules.

Question 3

Define a compound.

Answer 3

A compound consists of two or more different elements that are bonded chemically (Figure 2.1C). That is, the elements in a compound are not just mixed together: their atoms have joined in a chemical reaction. Many compounds, such as ammonia, water, and carbon dioxide, consist of molecules. But many others, like sodium sulfate (which we’ll discuss shortly) and silicon dioxide, do not.

Question 4

What are the two defining features of compounds?

Answer 4

1. The elements are present in fixed parts by mass (fixed mass ratio). This is so because each unit of the compound consists of a fixed number of atoms of each element.
2. A compound’s properties are different from the properties of its elements. Table 2.1 shows a striking example: soft, silvery sodium metal and yellow-green, poisonous chlorine gas are very different from the compound they form—white, crystalline sodium chloride, or common table salt!

Question 5

Define a mixture.

Answer 5

A mixture consists of two or more substances (elements and/or compounds) that are physically intermingled, not chemically combined.

Question 6

the law of mass conservation says _____

Answer 6

the total mass of substances does not change during a chemical reaction. The number of substances may change and, by definition, their properties must, but the total amount of matter remains constant.

Question 7

law of definite (or constant) composition says _____

Answer 7

no matter what its source, a particular compound is composed of the same elements in the same parts (fractions) by mass

Question 8

The fraction by mass (mass fraction) is _____

Answer 8

the part of the compound’s mass that each element contributes.

Question 9

The percent by mass (mass percent, mass %) is

Answer 9

he fraction by mass expressed as a percentage (multiplied by 100): Mass percent = mass fraction x 100

Question 10

Mass of element = _____

Answer 10

mass of compound x mass fraction

Question 11

The law of multiple proportions says _____

Answer 11

If elements A and B react to form two compounds, the different masses of B that combine with a fixed mass of A can be expressed as a ratio of small whole numbers. . .The law of multiple proportions tells us that in two compounds of the same elements, the mass fraction of one element relative to the other element changes in increments based on ratios of small whole numbers.

Question 12

Dalton expressed his theory in a series of postulates, presented here in modern terms: _____

Answer 12

1. All matter consists of atoms, tiny indivisible units of an element that cannot be created or destroyed.
2. Atoms of one element cannot be converted into atoms of another element. In chemical reactions, the atoms of the original substances recombine to form different substances.
3. Atoms of an element are identical in mass and other properties and are different from atoms of any other element.
4. Compounds result from the chemical combination of a specific ratio of atoms of different elements.

Question 13

Dalton’s postulates explain the mass laws: _____

Answer 13

• Mass conservation. Atoms cannot be created or destroyed (postulate 1) or converted into other types of atoms (postulate 2). Therefore, a chemical reaction cannot pos- sibly result in a mass change because atoms are just combined differently.
• Definite composition. A compound is a combination of a specific ratio of different atoms (postulate 4), each of which has a particular mass (postulate 3). Thus, each element in a compound must constitute a fixed fraction of the total mass.
• Multiple proportions. Atoms of an element have the same mass (postulate 3) and are indivisible (postulate 1). The masses of element B that combine with a fixed mass of element A must give a small, whole-number ratio because different numbers of B atoms combine with each A atom in different compounds.

Question 14

Explain cathode rays?

Answer 14

To discover the nature of an electric current, some investigators tried passing it through nearly evacuated glass tubes fitted with metal electrodes. When the electric power source was turned on, a “ray” could be seen striking the phosphor-coated end of the tube, which emitted a glowing spot of light.

Question 15

The main conclusion of experiments with cathode rays was _____

Answer 15

that cathode rays consist of negatively charged particles found in all matter. The rays become visible as their particles collide with the few remaining gas molecules in the evacuated tube. Cathode ray particles were later named electrons.

Question 16

The main conclusion of experiments surrounding electrons was that its mass was (relatively) _____

Answer 16

extremely small

Question 17

Who discovered the atomic nucleus and how?

Answer 17

1. Ernest Rutherford
2. Shot alpha particles at gold foil, for them to be deflected by the foil; the rare deflects led Rutherford to conclude that the “plum-pudding” model, instead concluding that all positive charge and mass of the atom was contained in a tiny region in the atom called the nucleus.

Question 18

An atom is _____

Answer 18

an electrically neutral, spherical entity composed of a positively charged central nucleus surrounded by one or more negatively charged electrons (Figure 2.7).

Question 19

An atom is neutral because _____

Answer 19

the number of protons in the nucleus equals the number of electrons surrounding the nucleus.

Question 20

An atomic nucleus consists of _____

Answer 20

The proton (p^+) has a positive charge, and the neutron (n^0) has no charge; thus, the positive charge of the nucleus results from its protons.

Question 21

The atomic number (Z) of an element equals _____

Answer 21

the number of protons in the nucleus of each of its atoms. All atoms of an element have the same atomic number, and the atomic number of each element is different from that of any other element.

Question 22

The mass number (A) is _____

Answer 22

the total number of protons and neutrons in the nucleus of an atom.

Question 23

The atomic symbol (or element symbol) of an element is _____

Answer 23

based on its English, Latin, or Greek name, such as C for carbon, S for sulfur, and Na for sodium (Latin natrium).

Question 24

Isotopes of an element are atoms that _____

Answer 24

have different numbers of neutrons and therefore different mass numbers. Most elements occur in nature in a particular iso- topic composition, which specifies the proportional abundance of each of its isotopes.

Question 25

All isotopes of an element have _____ chemical behavior

Answer 25

nearly identical

Question 26

The atomic mass unit (amu) is _____

Answer 26

1/12 the mass of a carbon-12 atom. The mass of an atom is measured relative to the mass of an atomic standard. The modern standard is the carbon-12 atom, whose mass is defined as exactly 12 atomic mass units.

Question 27

The isotopic composition of an element is determined by _____

Answer 27

mass spectrometry, a method for measuring the relative masses and abundances of atomic-scale particles very precisely

Question 28

isotopic mass is determined by _____

Answer 28

measured mass ratio x atomic mass unit of the substance

Question 29

the atomic mass (also called atomic weight) of an element is _____

Answer 29

the average of the masses of its naturally occurring isotopes weighted according to their abundances

Question 30

The mass of any given isotope of an element is _____, but the proportion of isotopes _____ from source to source.

Answer 30

1. constant

2. varies

Question 31

What is the organization of the modern periodic table of the elements?

Answer 31

a table of the elements listed by increasing atomic mass and arranged so that elements with similar chemical properties fell in the same column:

1. Each element has a box that contains its atomic number, atomic symbol, and atomic mass. (A mass in parentheses is the mass number of the most stable isotope of that element.) The boxes lie, from left to right, in order of increasing atomic number (number of protons in the nucleus).
2. The boxes are arranged into a grid of periods (horizontal rows) and groups (vertical columns). Each period has a number from 1 to 7. Each group has a number from 1 to 8 and either the letter A or B. A newer system, with group numbers from 1 to 18 but no letters, appears in parentheses under the number-letter designations. (The text uses the number-letter system and shows the newer group number in parentheses.)
3. The eight A groups (two on the left and six on the right) contain the main-group elements. The ten B groups, located between Groups 2A(2) and 3A(13), contain the transition elements. Two horizontal series of inner transition elements, the lanthanides and the actinides, fit between the elements in Group 3B(3) and Group 4B(4) and are placed below the main body of the table.

Question 32

The three categories of elements in the periodic table are _____

Answer 32

metals, nonmetals, and metalloids.

Question 33

Explain metals in the periodic table

Answer 33

The metals (three shades of blue in Figure 2.9) lie in the large lower-left portion of the table. About three-quarters of the elements are metals, including many main-group elements and all the transition and inner transition elements. They are generally shiny solids at room temperature (mercury is the only liquid) that conduct heat and electricity well. They can be tooled into sheets (are malleable) and wires (are ductile).

Question 34

Explain nonmetals in the periodic table

Answer 34

The nonmetals (yellow) lie in the small upper-right portion of the table. They are generally gases or dull, brittle solids at room temperature (bromine is the only liquid) and conduct heat and electricity poorly.

Question 35

Explain metalloids in the periodic table

Answer 35

The metalloids (green; also called semimetals), which lie along the staircase line, have properties between those of metals and nonmetals.

Question 36

In general, elements in a group have _____ chemical properties and elements in a period have _____ chemical properties.

Answer 36

1. similar

2. different

Question 37

Despite this classification of three types of elements, in reality, there is _____ from left to right and top to bottom [on the periodic table].

Answer 37

a gradation in properties

Question 38

Elements combine in two general ways and both involve the electrons of the atoms of interacting elements: _____

Answer 38

1. Transferring electrons from one element to another to form ionic compounds
2. Sharing electrons between atoms of different elements to form covalent compounds

Question 39

chemical bonds are defined as _____

Answer 39

the forces that hold the atoms together in a compound.

Question 40

ions form _____ compounds and are defined as _____

Answer 40

1. Ionic

2. charged particles that form when an atom (or small group of atoms) gains or loses one or more electrons

Question 41

The simplest type of ionic compound is _____, and it typically forms when _____

Answer 41

1. binary ionic compound, one composed of two elements.

2. a metal reacts with a nonmetal

Question 42

For binary ionic compounds,
• Each metal atom _____.
• Each nonmetal atom _____.

Answer 42

1. loses one or more electrons and becomes a cation, a positively charged ion
2. gains one or more of the electrons lost by the metal atom and becomes an anion, a negatively charged ion

Question 43

a monatomic ion is _____

Answer 43

A cation or anion derived from a single atom

Question 44

All binary ionic compounds are _____ of oppositely charged ions

Answer 44

solid arrays

Question 45

Coulomb’s law states _____

Answer 45

energy is proportional to (charge 1 x charge 2) / (distance between the charges)

Question 46

• Ions with higher charges attract (or repel) each other _____ than ions with lower charges.
• Smaller ions attract (or repel) each other _____ than larger ions, because the charges are closer to each other.

Answer 46

1. more strongly

2. more strongly

Question 47

The general rule for the number of electrons exchanged in the formation of an ionic bond is _____

Answer 47

For A-group elements, we usually find that metal atoms lose electrons and nonmetal atoms gain electrons to form ions with the same number of electrons as in an atom of the nearest noble gas

Question 48

Covalent substances form when _____

Answer 48

atoms of elements share electrons, which usually occurs between nonmetals.

Question 49

A covalent bond is defined as _____

Answer 49

A pair of electrons mutually attracted by the two nuclei

Question 50

Atoms of different elements _____ electrons to form the molecules of a covalent compound.

Answer 50

share

Question 51

There are two key distinctions between the chemical entities in covalent substances and those in ionic substances:

Answer 51

1. Most covalent substances consist of molecules. A cup of water, for example, consists of individual water molecules lying near each other. In contrast, under ordinary conditions, there are no molecules in an ionic compound. A piece of sodium chloride, for example, is a continuous array in three dimensions of oppositely charged sodium and chloride ions, not a collection of individual sodium chloride “molecules.”
2. The nature of the particles attracting each other in covalent and in ionic substances is fundamentally different. Covalent bonding involves the mutual attraction between two (positively charged) nuclei and the two (negatively charged) electrons that reside between them. Ionic bonding involves the mutual attraction between positive and negative ions.

Question 52

polyatomic ions are those where _____

Answer 52

two or more atoms bonded covalently and have a net positive or negative charge

Question 53

A chemical formula consists of _____

Answer 53

element symbols and, often, numerical subscripts show the type and number of each atom in the smallest unit of the substance

Question 54

The two general rules for formulas/naming of binary ionic compounds are _____

Answer 54

• For all ionic compounds, names and formulas give the positive ion (cation) first and the negative ion (anion) second.
• For all binary ionic compounds, the name of the cation is the name of the metal, and the name of the anion has the suffix -ide added to the root of the name of the nonmetal.

Question 55

The general rules for formula units are _____

Answer 55

• The subscript refers to the element symbol preceding it.
• The subscript 1 is understood from the presence of the element symbol alone (that
is, we do not write Ca1Br2).
• The charge (without the sign) of one ion becomes the subscript of the other:
Ca2+ Br1− gives Ca Br or CaBr 122
• Reduce the subscripts to the smallest whole numbers that retain the ratio of ions. Thus, for example, for the Ca21 and O22 ions in calcium oxide, we get Ca2O2, which we reduce to the formula CaO.*

Question 56

When two or more of the same polyatomic ion are present in the formula unit, that ion appears _____

Answer 56

in parentheses with the subscript written outside

Question 57

oxoanions are those in which _____

Answer 57

an element, usually a nonmetal, is bonded to one or more oxygen atoms

Question 58

hydrates are those molecules in which _____

Answer 58

there are a specific number of water molecules in each formula unit

Question 59

Binary covalent compounds are typically formed by

Answer 59

the combination of two non-metals.

Question 60

The naming rules for binary covalent compounds are: _____

Answer 60

• The element with the lower group number in the periodic table comes first in the name. The element with the higher group number comes second and is named with its root and the suffix -ide. For example, nitrogen [Group 5A(15)] and fluorine [Group 7A(17)] form a compound that has three fluorine atoms for every nitrogen atom. The name and formula are nitrogen trifluoride, NF3. (Exception: When the compound contains oxygen and any of the halogens chlorine, bromine, or iodine, the halogen is named first.)
• If both elements are in the same group, the one with the higher period number is named first. Thus, one compound that the Group 6A(16) elements sulfur (Period 3) and oxygen (Period 2) form is sulfur dioxide, SO2.
• Covalent compounds use Greek numerical prefixes (see Table 2.6) to indicate the number of atoms of each element. The first element in the name has a prefix only when more than one atom of it is present; the second element usually has a prefix.

Question 61

Hydrocarbons, the simplest type of organic compound, contain _____

Answer 61

only hydrogen and carbon.

Question 62

molecular mass is found via _____

Answer 62

sum of atomic masses

Question 63

formula mass is defined _____

Answer 63

Ionic compounds don’t consist of molecules, so the mass of a formula unit is called the formula mass instead of molecular mass: the number of atoms of each element inside the parentheses is multiplied by the subscript outside the parentheses

Question 64

The four representations of molecules with formulas and models are _____

Answer 64

1. molecular formula
2. structural formula
3. ball-and-stick model
4. space-filling model.

Question 65

Explain heterogenous mixtures.

Answer 65

A heterogeneous mixture has one or more visible boundaries between the components. Thus, its composition is not uniform, but rather varies from one region to another. Many rocks are heterogeneous, having individual grains of different minerals. In some heterogeneous mixtures, such as milk and blood, the boundaries can be seen only with a microscope.

Question 66

Explain homogenous mixtures

Answer 66

A homogeneous mixture (or solution) has no visible boundaries because the components are individual atoms, ions, or molecules. Thus, its composition is uniform. A mixture of sugar dissolved in water is homogeneous, for example, because the sugar molecules and water molecules are uniformly intermingled on the molecular level. We have no way to tell visually whether a sample of matter is a substance (element or compound) or a homogeneous mixture.

Question 67

aqueous solutions are defined as _____

Answer 67

Solutions in water