Chapter 2

Question 1

Bohr atomic model

Answer 1

An early atomic model in which electrons were assumed to revolve around the nucleus in discreet orbitals

Question 2

Pauli exclusion principle

Answer 2

The postulate that for an individual atom, at most two electrons, which necessarily have opposite spins, can occupy the same state

Question 3

Atomic mass unit (amu)

Answer 3

A measure of atomic mass, 1/12 the mass of an atom of 12C

Question 4

Atomic number (Z)

Answer 4

For a chemical element, the number of protons within the atomic nucleus

Question 5

Atomic weight (A)

Answer 5

The weighted average of the atomic masses of an atom’s naturally occurring isotopes. Can be in amu or mass per mole of atoms

Question 6

Bonding energy

Answer 6

The energy required to separate two atoms that are chemically bonded to each other. Can be expressed on a per-atom basis or per mole of atoms

Question 7

Coulombic force

Answer 7

A force between charged particles such as ions; the force is attractive when the particles are of opposite charge

Question 8

Covalent bond

Answer 8

A primary interatomic bond that is formed by the sharing of electrons between neighboring atoms that have similar electronegativities. Normally s and p orbitals are involved. Have variable bond energies, are directional, and are found in semiconductors, ceramics, and polymer chains.

Question 9

Dipole (electric)

Answer 9

A pair of equal and opposite electrical charges separated by a small distance

Question 10

Electron configuration

Answer 10

For an atom, the manner in which possible electron states are filled with electrons

Question 11

Electron state

Answer 11

One set of discrete, quantized energies that are allowed for electrons. In the atomic case, each state is specified by four atomic numbers

Question 12

Electronegative

Answer 12

For an atom, having the tendency to accept valence electrons. Also used to describe nonmetallic elements

Question 13

Electropositive

Answer 13

For an atom, having the tendency to release valence electrons. Also used to describe metallic elements

Question 14

Ground state

Answer 14

A normally filled electron energy state from which an electron excitation may occur

Question 15

Hydrogen bond

Answer 15

A strong secondary interatomic bond that exists between a bound hydrogen atom (its unscreened proton) and the electrons of adjacent atoms

Question 16

Ionic bond

Answer 16

A coulombic interatomic bond that exists between two adjacent and oppositely charged ions that requires the transfer of electrons and a large difference in electronegativity. They have large bond energy, are nondirectional, and are found in ceramics.

Question 17

Isotope

Answer 17

Atoms of the same element that have different atomic masses

Question 18

Metallic bond

Answer 18

A primary interatomic bond involving the nondirectional sharing of nonlocalized valence electrons (sea of electrons) that are mutually shared by all the atoms in the metallic solid. Have variable bond energies, are nondirectional, and are found in metals.

Question 19

Mole

Answer 19

The quantity of a substance corresponding to 6.022 * 10^23 atoms or molecules

Question 20

Periodic table

Answer 20

The arrangement of the chemical elements with increasing atomic number according to the periodic variation in electron structure. Nonmetallic elements are positioned to the far right-hand side of the table

Question 21

Polar molecule

Answer 21

A molecule in which there exists a permanent electric dipole moment by virtue of the asymmetrical distribution of positively and negatively charged regions

Question 22

Primary bonds

Answer 22

Interatomic bonds that are relatively strong and for which bonding energies are relatively large. Types: ionic, covalent, metallic

Question 23

Quantum mechanics

Answer 23

A branch of physics that deals with atomic and subatomic systems; it allows only discrete values of energy. By contrast, for classical mechanics, continuous energy values are permissible

Question 24

Quantum number

Answer 24

A set of four numbers, the values of which are used to label possible electron states. Three of the quantum numbers are integers that specify the size (n), shape (l), and spatial orientation (ml) of an electron’s probability density; the fourth number designates spin orientation (ms).

Question 25

Secondary bond

Answer 25

Interatomic and intermolecular bonds that are relatively weak and for which bonding energies are relatively small. Normally, atomic or molecular dipoles are involved. Ex: van der Waals forces and hydrogen bonding. They are directional and either inter-chain (polymer) or inter-molecular.

Question 26

Valence electron

Answer 26

The electrons in the outermost occupied electron shell, which participate in interatomic bonding and they tend to determine an atom’s chemical properties

Question 27

Van der Waals bond

Answer 27

A secondary interatomic bond between adjacent molecular dipoles with asymmetrical electron fields that may be permanent or induced

Question 28

Wave-mechanical model

Answer 28

An atomic mode in which electrons are treated as being wavelike

Question 29

What properties are determined by an atom’s electronic structure?

Answer 29

• Chemical
• Electrical
• Thermal
• Optical

Question 30

What are the number of states and electrons in s,p,d, and f subshells?

Answer 30

s: 1 state 2 electrons
p: 3 states 6 electrons
d: 5 states 10 electrons
f: 7 states 14 electrons

Question 31

When are electron configurations stable?

Answer 31

When their electron states/orbitals are full

Question 32

Why are filled energy shells more stable?

Answer 32

They require more energy to gain or lose atoms

Question 32

What trend does atomic radius follow?

Answer 32

Increases from right to left and top to bottom on the periodic table

Question 32

What trend do ionization energy and electronegativity follow?

Answer 32

Increases from left to right and bottom to top

Question 33

What is the most common mixed bonding type?

Answer 33

Covalent-Ionic

Question 34

How do melting point, elastic modulus, and thermal expansion relate to bond energy?

Answer 34

Melting point and elastic modulus increase (becomes stiffer) as bond energy increases and thermal expansion decreases

Question 35

What is the most common bonding type for ceramics?

Answer 35

Ionic bonding

Question 36

What are some characteristics of covalent bonds?

Answer 36

• Strong bonds
• High melting points
• Directional (atoms form chains to get the right bonding angle/direction)
• Common in polymers (formation of chains)

Question 37

Why do polymers have low melting points?

Answer 37

Polymers have Van der Waals bonds between their polymer chains, which are weak bonds

Question 38

What is the relationship between bond energy and thermal expansion?

Answer 38

A higher bond energy correlates with lower thermal expansion. The bonds resist the expansion

Question 39

What type of bonds are found in ceramics?

Answer 39

Ionic and covalent bonding
- High bond energy
- High melting points
- Low thermal expansion

Question 40

What types of bonds are found in metals?

Answer 40

Metallic bonds
- Moderate bond energy
- Moderate melting points
- Moderate thermal expansion

Question 41

What type of bonds are found in polymers?

Answer 41

Covalent and secondary bonds
- Low bond energy
- Low melting points
- High thermal expansion

Question 42

What properties are determined by electron structure?

Answer 42

• Chemical
• Electrical
• Thermal
• Optical

Question 43

What does the percent ionic character of a mixed covalent-ionic bond depend on?

Answer 43

Electronegativity