Bonding And Structure

Question 1

Covalent bond definition

Answer 1

A covalent bond is the electrostatic attraction between two nuclei and a shared pair of electrons.

Question 2

Ionic bond definition

Answer 2

An ionic bond is the electrostatic attraction between two ions of opposite charges

Question 3

Metallic bond definition

Answer 3

A metallic bond is the electrostatic attraction between positively charged metal ions and delocalised electrons.

Question 4

Intermolecular forces definition

Answer 4

Intermolecular forces are the weak forces of attraction that exist between molecules

Question 5

Electrostatic definition meaning

Answer 5

Electrostatic attraction is the attraction between positively-charged and negatively-charged particles (eg. protons &
electrons, + and – ions or + ions and electrons)

Question 6

Crystal structure definition

Answer 6

The crystal structure of a substance is the type of structure it has: giant covalent lattice, simple molecular covalent,
giant ionic lattice, or giant metallic lattice.

Question 7

Metallic lattice definition

Answer 7

A metallic lattice is a giant, regular, repeating structure of positive metal ions existing in a ‘sea’ of delocalised
electrons.

Question 8

Ionic lattice definition

Answer 8

An ionic lattice is the arrangement of ions into a large structure, consisting of alternating positive ions and negative
ions.

Question 9

What 2 things affect the strength of an ionic bond?

Answer 9

1. Ionic charge; the greater the charge of an ion, the stronger the ionic bond; and therefore the greater the melting/ boiling point
2. Ionic radii; smaller ions can pack more closely, the closer the ions, the greater the electrostatic attraction and ionic bond. So smaller ionic compounds have higher melting/ boiling points than larger ions

Question 10

How do you know if there’s a single, double or triple covalent bond?

Answer 10

• 1 pair of shared electrons is single
• 2 pairs of shared electrons is double
• 3 pairs of shared electrons is triple

Question 11

What is dative covalent bonding?

Answer 11

It’s when both electrons come from 1 atom

Question 12

What is so special about covalent bonds in AlCl3?

Answer 12

• the Aluminium in the molecule doesn’t have a full outer shell (it only has 6), this means that 1 molecule can bond to another AlCl3 molecule to form Al2Cl6

Question 13

What is the difference between a lone pair of electrons and a bonding pair of electrons?

Answer 13

A bonding pair means they were used in the covalent bond and are shared between 2 atoms, a lone pair is ones that are leftover and not shared.

Question 14

Do lone pairs or bonding pairs give a larger angle?

Answer 14

Lone pair/ lone pair angles are the biggest, lone pair/ bonding pair are the second biggest and bonding pair/ bonding pair are the smallest

Question 15

What are the different shapes of molecules with 2 electron pairs around the central atom?

Answer 15

linear;
- angle of 180
- e.g. CO2, BeCl2

Question 16

What are the different shapes of molecules with 3 electron pairs around the central atom?

Answer 16

Trigonal planar;
- 120 degrees
- e.g. BF3, BCl3, SO3, NO3-

Question 17

What are the different shapes of molecules with 4 electron pairs around the central atom?

Answer 17

Tetrahedral;
- no lone pairs
- 109.5 degrees
- e.g. CH4, SO4 2-, SiCl4, NH4

Bent;
- 2 lone pairs
- 104.5 degrees
- e.g. H20

Trigonal Pyramidal;
- 1 lone pair
- 107 degrees
- e.g. SO3 2-, NH3

Question 18

What are the different shapes of molecules with 5 electron pairs around the central atom?

Answer 18

Trigonal bipyramidal;
- 90 degrees, 120 degrees
- e.g. PCl5

Question 19

What are the different shapes of molecules with 6 electron pairs around the central atom?

Answer 19

Octahedral;
- 90 degrees
- SF6

Question 20

What are some properties of giant covalent structures?

Answer 20

~ very high melting points-you need to break a lot of bonds to melt/ boil the substance, and this requires lots of energy
~ extremely hard-because of the strong bonds through ought the lattice
~ good thermal conducts-because vibrations travel easily through the stiff lattice
~ insoluble-covalent bonds means atoms are more attracted to their neighbouring atoms, than the solvent molecules
~ can’t conduct electricity because ther is no free ions or delocalised electrons that can move freely and carry charge

Question 21

Electronegativity definition

Answer 21

The ability of an atom to attract bonding electrons in a covalent bond. Electronegativity can be measured by the Pauling scale, higher nuclear charges and smaller atomic radii increases the Electronegativity of an element ( Fluorine is the most electronegative element in the periodic table).

Question 22

How can bonding electrons be affected by Electronegativity?

Answer 22

If both atoms in a covalent bond have similar or identical electronegativities, the bonding electrons are approximately halfway between the atoms, and the bond will be non-polar. Examples include homonuclear, diatomic nuclear gases such as H2, Cl2.
If two atoms have different electronegativities, the bonding electrons will be attracted to the more electronegative atom, causing each atom to be slightly charged, this means the bond is polar.
In a polar bond, the difference in electronegativities of the atoms causes a dipole. A dipole is a difference in charge between 2 atoms caused a shift in electron density in the bond.
So the greater the difference in electronegativities, the greater the shift in electron density and the more polar the bond.

Question 23

How can bonding electrons be affected by Electronegativity?

Answer 23

If both atoms in a covalent bond have similar or identical electronegativities, the bonding electrons are approximately halfway between the atoms, and the bond will be non-polar. Examples include homonuclear, diatomic nuclear gases such as H2, Cl2.
If two atoms have different electronegativities, the bonding electrons will be attracted to the more electronegative atom, causing each atom to be slightly charged, this means the bond is polar.
In a polar bond, the difference in electronegativities of the atoms causes a dipole. A dipole is a difference in charge between 2 atoms caused a shift in electron density in the bond.
So the greater the difference in electronegativities, the greater the shift in electron density and the more polar the bond.

Question 24

What type of intermolecular forces are there?

Answer 24

~ London forces (instantaneous dipole induced dipole bonds)
~ permanent dipole-permanent dipole bonds
~ hydrogen bonds (strongest type of intermolecular forces)

Question 25

What are London forces?

Answer 25

• cause all atoms and molecules to be attracted to each other
• electrons in charge clouds move really quickly, at any particular moment, electrons in an atom are likely to be more on one side than the other. At this moment, atom would have a temporary dipole
• this dipole can induce another temporary dipole in the opposite direction on a neighbouring atom. The two dipoles are then attracted to each other. This can become a domino effect.
• electrons are constantly moving, the dipoles are being created and destroyed all the time. Overall, the atoms are attracted to each other
• larger molecules have larger electron clouds, meaning stronger London forces
• molecules with a larger surface area have a higher exposed electron cloud, so have stronger London forces

Question 26

What are permanent dipole permanent dipole forces?

Answer 26

• The δ- and δ+ charges on molecules can cause weak electrostatic forces of attractions between molecules, e.g. hydrogen chloride gas.
• Permanent dipole permanent dipole bonds happen as well as London forces not instead.
• So molecules that have both London forces and permanent dipole permanent dipole forces generally have higher boiling and melting points than those with similar London forces but no permanent dipole permanent dipole forces.

Question 27

What is hydrogen bonding?

Answer 27

• Covalent bonding only happens when hydrogen is covalently bonded to nitrogen, oxygen or fluorine.
• nitrogen, oxygen and fluorine are very electronegative, so draw the bondong electrons away from the hydrogen atom.
• the bond is so polarised, and hydrogen has such a high charge density because its so small, that hydrogen forms weak bonds with lone pairs of electrons from nitrogen, fluorine or oxygen atoms of other molecules.
• examples include: water, ammonia and hydrogen fluoride
• organic molecules that often form hydrogen bonds include alcohols and amine groups (-OH, -NH)
• substances that form hydrogen bonds are also soluble in water, because they can form hydrogen bonds with the water

Question 28

How do hydrogen bonding explain why ice floats on water?

Answer 28

• ice is an example of a simple molecular structure
• in ice, the water molecules are arranged so that there is the maximum number of hydrogen bonds - the lattice structure formed this way wastes lots of space
• as the ice melts , some of the hydrogen bonds are broken and the lattice breaks down, allowing molecules to fill the spaces
• this effect means ice is much less dense than water - which is why ice floats

Question 29

How is solubility affected by bonding?

Answer 29

1. Bonds in the substance have to break
2. Bonds in the solvent have to break
3. New bonds have to form between the substance and the solvent

Question 30

What are polar solvents?

Answer 30

• made of polar molecules, such as water. Water molecules bond to each other with hydrogen bonds. Not all polar solvents form hydrogen bonds. E.g. propanone only forms London forces and permanent dipole permanent dipole forces

Question 31

What are non-polar molecules?

Answer 31

Are made of molecules that are not polar. E.g. hexane, bond to each other through London forces

Question 32

How do ionic substances dissolve in polar solvents?

Answer 32

• When an ionic substances mix in water, the ions in the ionic substance are attracted to the oppositely charged ends of the water molecules, the ions are pulled away from the ionic lattice and the water molecules surround the ions, this is called hydration. Some ionic substances don’t dissolve because their ionic bonds are too strong

Question 33

Do halogenoalkenes dissolve in water and why?

Answer 33

• they contain polar bonds but their dipoles aren’t strong enough to form hydrogen bonds with water
• the hydrogen bonding between water molecules is stronger than the bonds that would be formed with halogenoalkanes, so halogenoalkanes don’t dissolve
• but halogenoalkanes can form permanent dipole permanent dipole bonds, and can dissolve in polar solvents tha form permanent dipole permanent dipole bonds