Bond Types

Question 1

Properties of Ionic Compounds?

Answer 1

ionic bonding model, physical behavior, electrical conductivity, and thermal conductivity

Question 2

Physical Behavior of Ionic Compounds

Answer 2

Ionic Compounds tend to be hard (do not dent), rigid (do not bend), and brittle (crack without deforming)

• optimum distance is at the greatest negative potential energy

Question 3

Why do ionic compounds crack?

Answer 3

stress from opposing (two opposite) directions creates a cleavage plane among the metal and nonmetal connections, pushing like charges closer together

too close of a connection between like charges will create a repulsion (which makes the crack)

Question 4

Electrical Conductivity in Ionic Compounds

Answer 4

• a solid ionic compound (made up of positive and negative ions) does not conduct electricity in the solid state; the ions are fixed in the solid state in the lattice and do not move
• when melted or dissolved, ionic compounds conduct electricity; in the liquid state or in solution, the ions are free to move and carry a current

Question 5

Thermal Conductivity of Ionic Compounds

Answer 5

• they have high melting points and even higher boiling points (nearly twice as high)
• melting to a liquid state just changes relative position, while boiling break the attractions

Question 6

Why does MgO have a much higher melting point and boiling point compared to other ionic compounds?

Answer 6

• the ions (Mg 2+ and O2- ) creates a very stable compound/lattice
• unique crystal structure to create tightly packed compound
• covalent characters

all these pack the ions closer together and tighter, meaning the melting point and boiling points need to be much higher to change the solid state

Question 7

Covalent Bonding Model

Answer 7

• covalent bonding involves the sharing of electrons and is usually observed when a nonmetal bonds to a nonmetal
• covalent bonds arise from the balance between the nuclei attracting the electrons, and electrons and nuclei repelling each other
• the optimum distance between the bonds are when they are at their lowest potential energy

Question 8

Bonding Pair in Covalent Bonds

Answer 8

atoms share electrons to achieve a full outer level of electrons; also called a shared pair

Example: H-H (shared pair in middle)

Question 9

Lone Pairs

Answer 9

• an outer-level electron pair that is not involved in bonding; also called an unshared pair

Example: extra electrons around an element that are not connected to others

Question 10

Properties of a Covalent Bond

Answer 10

bond order

bond energy (BE, bond enthalpy or bond strength)

Bond length

Question 11

Bond Order in Covalent Bonds

Answer 11

• number of electron pairs being shared by a given pair of atoms
• consists of single, double and triple bonds

Question 12

Single Covalent Bond

Answer 12

consists of one bonding pair and has bond order of 1

Question 13

Double Covalent Bond

Answer 13

consists of two bonding electron pairs, four electrons shared between two atoms, so the bond order is 2

Question 14

Triple Covalent Bond

Answer 14

consists of three shared pairs: two atoms share six electrons, so the bond order is 3

Question 15

Bond Energy in Covalent Bonds (bond enthalpy or bond strength)

Answer 15

• bond energy decreases down a group and increases across the period

strength depends on magnitude of the attraction between the nuclei and shared electrons (charge) energy needed to overcome the attraction between the nuclei and the shared electrons

• signified as delta H

standard entahlpy change for breaking bond in 1 mol of gaseous molecules (equation in study guide)

Question 16

bond length in Covalent Bonds

Answer 16

• distance between the nuclei of the bonded atoms

bond length increases down a group and decreases across the period

• atom size in periodic table increase down the group and increase across the period; so as atoms go down the table, nuclear distance increases since size increases)

Question 17

Note difference between bond length and bond energy

Answer 17

• bond length increases down a group and decreases across the period
• bond energy decreases down a group and increases across the period (growing nuclear charge creates more stability/energy going left to right for period)

Question 18

Covalent Compounds

Answer 18

molecular covalent substances and network covalent solids

Question 19

Molecular covalent substances Forces

Answer 19

• individual molecules
• strong intramolecular forces
• much weaker intermolecular forces

Example: methane and ammonia(gases), benzene and water(liquids), and sulfur and paraffin wax (low melting solids)

Question 20

Network covalent solids Forces

Answer 20

• no separate molecules
• strong intramolecular forces (covalent bonds between atoms throughout sample)

Question 21

Physical Properties: Molecular Covalent Compounds vs Network Covalent Solids

Answer 21

• molecular covalent compounds are soft and have a low melting and boiling point; from weak intermolecular interactions(not based around covalent bonds); (water)
• network covalent solids are hard and have high melting point, because covalent bonds join all the atoms in the sample (quarts and diamond)

Question 22

Electrical conductivity in Covalent Compounds

Answer 22

most are poor electrical conductors, whether melted or dissolved; no ions present

Question 23

Metallic Bonding

Answer 23

-involves electric pooling and occurs when a metal bonds to another metal

• All metal atoms in the sample contribute their
  valence electrons to form a delocalized electron
  “sea”:
• The metal “ions” (nuclei with core electrons) lie in an orderly array within this mobile sea
• All the atoms in the sample share the electrons
• The metal is held together by the attraction between the metal “cations” and the “sea” of valence electrons
• sea has regularity (not rigidity) of metal-ion array number, and mobility of the valence electrons

Question 24

Properties of metals

Answer 24

• electron sea model
• melting points and boiling points
• mechanical properties
• electrical conductivity

Question 25

Melting and Boiling Points of Metals

Answer 25

boiling point much higher than melting point (melting point shifts, boiling point breaks)

• Down a group, melting points decrease because the larger metal ions have a weaker attraction to the electron sea.
• Across a period, melting points increase. Alkaline earth metals [Group 2A(2)] have higher
  melting points than alkali metals [Group 1A(1)] because their 2+ cations have stronger attractions to twice as many valence electrons (more options of valence electrons to be filled)

Question 26

Mechanical Properties of Metals

Answer 26

• can be shaped without breaking (malleable)
• (metal ions do not repel each other, electron sea allows metal ions to slide past each other)

Question 27

Electrical Conductivity of Metals

Answer 27

• good conductors of electricity in both solid and liquid state (electron sea mobile in both phases)
• good conductors of heat (mobile electrons make metals good conductors of heat)