Chapter 6 - Bonding and structure

Question 1

What is ionic bonding ?

Answer 1

Ionic bonding is the electrostatic attraction between oppositely charged ions

Question 2

What is covalent bonding ?

Answer 2

Covalent bonding is the strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

Question 3

What is the electron pair repulsion theory ?

Answer 3

It explains and predicts the shapes of molecules and polyatomic ions

Question 4

What is the order of pair repulsion, strongest to weakest?

Answer 4

• Lone-Lone
• Bonded-Lone
• Bonded-Bonded

Question 5

What is a lone pair of electrons ?

Answer 5

• A lone pair refers to a pair of electrons that are not shared with another atom in a covalent bond
• Lone pairs repel more strongly compared to bonding pairs
• Every lone pair decreases the bond angle by 2.5 degrees

Question 6

What shape is a molecule with no lone pairs ?

Answer 6

• Tetrahedral, 109.5 degree bond angle

- For example, CH4

Question 7

What shape is a molecule with one lone pair ?

Answer 7

• Trigonal pyramidal, 107 degree bond angle

- For example, NH3

Question 8

What shape is a molecule with two lone pairs ?

Answer 8

• Non-linear, 104.5 degree bond angle

- For example, H2O

Question 9

What shape is a molecule with two bonded pairs ?

Answer 9

• Linear, 180 degree bond angle

- For example, CO2

Question 10

What shape is a molecule with three bonded pairs ?

Answer 10

• Trigonal planar, 120 degree bond angle

- For example, BF3, boron trifluoride

Question 11

What shape is a molecule with four bonded pairs ?

Answer 11

• Tetrahedral, 109.5 degree bond angle

- For example, CH4

Question 12

What shape is a molecule with five bonded pairs ?

Answer 12

• Trigonal Bipyramidal

- There are actually two bond angles, 120 degrees in one plane and 90 degrees in another plane

Question 13

What shape is a molecule with 6 bonded pairs ?

Answer 13

• Octahedral, 90 degree bond angles

- For example, SF6 Sulfur hexafluoride

Question 14

Carbonate ion

Answer 14

CO3 (2-), Trigonal Planar, 120 degree bond angles

Question 15

Nitrate ion

Answer 15

NO3(-), Trigonal planar, 120 degree bond angles

Question 16

Sulfate ion

Answer 16

SO4(2-), tetrahedral, 109.5 degree bond angles

Question 17

What is electronegativity ?

Answer 17

The ability of an atom to attract the bonding electrons in a covalent bond

Question 18

How is electronegativity measured ?

Answer 18

• It is measured on the Pauling scale
• A higher value on the Pauling scale means it has higher electronegativity and thus a greater attraction for an electron pair in a covalent bond

Question 19

What do Pauling values depend on ?

Answer 19

• Depends on an elements position in the table
• Across the periodic table, the nuclear charge increases and the atomic radius decreases
• As you go up and across the table, the values increase

Question 20

Covalent or ionic

Answer 20

• Covalent bonds have an electronegativity difference of 0
• Polar covalent bonds have an electronegativity difference between 0 and 1.8
• Ionic bonds have an electronegativity difference of more than 1.8

Question 21

What makes a bond polar ?

Answer 21

• Two atoms with an electronegativity difference of at least 0.5, the bonding electrons are pulled more towards the more electronegative atom
• A polar bond forms a dipole

Question 22

How is a dipole formed ?

Answer 22

• A difference in charge between the two atoms

- A dipole in a polar covalent bond is a permanent dipole

Question 23

What happens if the polar bonds are arranged symmetrically in a molecule ?

Answer 23

The dipoles cancel each other out, so the molecule has no overall dipole and is non polar

Question 24

What happens if the polar bonds are arranged unsymmetrically in a molecule ?

Answer 24

Uneven distribution of charge and the molecule will have an overall dipole

Question 25

What are the three types of IMFs ?

Answer 25

- Induced dipole dipole interactions AKA London Forces - Permanent dipole dipole interactions - Hydrogen bonding

Question 26

What are London Forces ?

Answer 26

- Weak IMFs that exist between all molecules, polar or non polar - They act between induced dipoles in different molecules, only temporary dipoles

Question 27

How do induced dipoles come around ?

Answer 27

- Movement of electrons produces a changing dipole in a molecule - An instantaneous dipole will exist, but its position will be changing - The instantaneous dipole induces a dipole in a neighbouring molecule - The induced dipole induces further dipoles on neighbouring molecules, which then attract more and more

Question 28

What effect does the amount of electrons have on boiling point?

Answer 28

- The more electrons - The larger the instantaneous and induced dipoles - The greater the induced dipole dipole reactions - The stronger the London forces - The higher their boiling point

Question 29

What are Permanent dipole dipole interactions ?

Answer 29

- Permanent dipole dipole interactions act between the permanent dipoles in different polar molecules - The delta negative part in one molecule is attracted to the delta positive part in another molecule

Question 30

How much energy is required to break permanent dipole-dipole interactions ?

Answer 30

- More energy is required as it is stronger than London forces. - If you have permanent dipoles you are likely to also have London forces

Question 31

What is the MP and BP like for simple molecular substances ?

Answer 31

They have a low melting and boiling point, this is due to the fact that a little bit of energy is required to break the weak IMFs

Question 32

What is the solubility of Non-Polar Simple Molecules like in non polar solvent ?

Answer 32

- IMFs form between the two - Interactions weaken the IMFs in the lattice - IMF breaks and the compound dissolves

Question 33

What is the solubility of Non-Polar Simple Molecules like in polar solvents ?

Answer 33

- There are little interactions between molecules in the lattice and in the solvent - Bonding within the polar solvent is too strong to be broken

Question 34

What is the solubility of Polar Simple Molecules like ?

Answer 34

Polar covalent substances may dissolve in polar solvents. This is due to the fact that the polar solute molecules and the polar solvent molecules can attract each other

Question 35

How do intermolecular forces explain simple covalent compounds not conducting electricity?

Answer 35

Covalent molecules are uncharged as the permanent dipoles are not strong enough. This means they can not carry charge.

Question 36

What is Hydrogen Bonding ?

Answer 36

- Hydrogen bonding is the intermolecular bonding between the lone pair of electrons in molecules containing N, O or F and a H atom - It acts between a lone pair of electrons and a hydrogen in a different molecule

Question 37

What are some anomalous properties of water ?

Answer 37

- Ice is less dense than water - Water has a high MP and BP - It has a high surface tension - Water has a high viscosity

Question 38

Why is ice less dense than water ?

Answer 38

- In ice, water molecules are held together in an open tetrahedral lattice that is full of holes - When ice melts, hydrogen bonds are broken, so ice has more of these than water. As hydrogen bonds are long, this causes ice to be less dense than water.

Question 39

Why does water have a high MP and BP ?

Answer 39

Water has both London forces and hydrogen bonds which mean more energy is needed to break these bonds.