1.3 - Bonding

Question 1

State and explain the trend in electronegativities across period 3 from sodium to sulfur

Answer 1

Electronegativity increases
Number of protons increase
Same number of shells/shielding is the same
Attraction of bond pair to nucleus increases

Question 2

Explain why the oxides of sodium and phosphorus have different melting points. In your answer you should discuss the structure of bonding in these oxides, and the link between electronegativity and the type of bonding.

Answer 2

Large difference in electronegativity leads to ionic bond
Oxides of Na are a giant ionic lattice
Strong forces of attraction between oppositely charged ions
Oxides of P have covalent bonds and are simple molecular
Weak intermolecular forces between molecules
Melting point of sodium oxide is greater than phosphorus oxide.

Question 3

What is ionic bonding?

Answer 3

Strong electrostatic forces of attraction between oppositely charged ions.

Question 4

Explain the properties of ionic compounds.

Answer 4

Ionic compounds conduct electricity only when they’re molten or dissolved, because the ions are free to move and they carry a charge. Ionic compounds have high melting points because of the strong electrostatic forces. Ionic compounds are soluble in water because water is polar and attracts both the positive and negative ions in the ionic compound.

Question 5

What is covalent bonding?

Answer 5

Two atoms share electrons so that they’ve both got full outer shells of electrons. Both the positive nuclei are attracted electrostatically to the charged electrons.

Question 6

What is the structure of graphite and its properties?

Answer 6

Weak intermolecular forces between the layers in graphite are easily overcome, so the sheets can slide over each other. Graphite is used as a dry lubricant and in pencils. The delocalised electrons are free to move and carry a charge, so it is an electrical conductor. The layers are far apart compared to the length of the covalent bonds, so graphite has a low density and is used to make strong, lightweight sports equipment. High melting point due to the strong covalent bonds. Graphite is insoluble.

Question 7

Describe the structure and properties of diamond.

Answer 7

Each carbon atom is covalently bonded to four other carbon atoms, arranged in a tetrahedral shape. Diamond has a high melting point, is hard (used in diamond-tipped drills and saws). Vibration travels easily though the stiff lattice, so it’s a good thermal conductor. Cannot conduct electricity as there are no delocalised electrons. Insoluble. Refracts light.

Question 8

What is coordinate bonding?

Answer 8

An atom donates a pair of electrons to another atom.

Question 9

Describe bonding pairs.

Answer 9

Electron pairs will repel each other as much as they can. Lone pairs repel each other the most, then lone pair to bonding pair, then bonding pair to bonding pair.

Question 10

Shapes of molecules

Answer 10

BeCl2, linear, 180°
BF3, trigonal planar, 120°
NH4^+, tetrahedral, 109.5°
PF3, trigonal pyramidal, 1 lp, 107°
H2O, bent, 2 lp, 104.5°
PCl5, trigonal bipyramidal, 120° and 90°
SF4, seesaw, 1 lp, 102° (exam questions say 118°) and 87°
ClF3, T-shaped, 2 lp, 88°
SF6, octahedral, 90°
XeF4, square planar, 2 lp, 90°
If 5 bonding pairs and 1 lp, then shape like SF6

Question 11

What is electronegativity?

Answer 11

The ability of an atom to attract an electron pair in a covalent bond. Fluorine, oxygen, nitrogen and chlorine are strongly electronegative.

Question 12

What makes a bond polar?

Answer 12

Large difference in electronegativity between atoms. In a polar bonds the difference in electronegativity between the two atoms causes a permanent dipole. A dipole is a difference in charge between the two atoms caused by a shift in electron density in the bond.

Question 13

How can whole molecules be polar?

Answer 13

Uneven distribution of charge across a whole molecule. If polar bonds are arranged symmetrically in the molecule, there is no permanent dipole. For a substance made up of molecules that have permanent dipoles, there will be weak electrostatic forces of attraction on neighbouring molecules. If you put a charged rod next to a jet of polar liquid, like water, the liquid will move towards the rod as there are both positive and negative charges.

Question 14

What are the 3 intermolecular forces

Answer 14

Van Der waals, dipole-dipole, Hydrogen bonding.

Question 15

What causes Van der waals?

Answer 15

Electrons are constantly moving around the atom, where it can be more to one side than the other, causing a temporary dipole. This induces a dipole in a neighbouring atom. More dipoles are caused.

Question 16

Describe the structure of iodine.

Answer 16

It is a solid at room temperature. The van der waals forces hold them together in a lattice. But the iodine atoms are held together by strong covalent bonds.

Question 17

What affects van der waals forces?

Answer 17

Larger molecules have more electrons so stronger van der waals. Long straight molecules lie closer together so they are stronger than branched molecules. More vdw forces = higher boiling points.

Question 18

What is hydrogen bonding.

Answer 18

Strongest intermolecular force. Only when hydrogen is covalently bonded to NOF because they are electronegative and draw binding electrons away from the hydrogen atom, making it polarised. Water and ammonia both have H bonding. You must draw the lone pairs on the NOF, delta charges, straight lines…

Question 19

What effect does hydrogen bonding have on the properties of substances?

Answer 19

Higher melting and boiling points. As liquid water cools to form ice, the molecules make more hydrogen bonds and arrange themselves into a regular lattice structure. In this regular structure, the H2O molecules are further apart on average than the molecules in liquid water, so ice is less dense than liquid water.

Question 20

Describe metallic bonding and properties.

Answer 20

Giant metallic lattice structures. Positive metal ions are attracted to the sea of delocalised electrons. The more delocalised electrons per ion, the stronger the attraction. The delocalised electrons can pass kinetic energy to each other, making metals good thermal conductors. Metals are good electrical conductors because the delocalised electrons can move and carry a charge. Metals are insoluble because of the strong metallic bonds.

Question 21

Describe solids, liquids and gases.

Answer 21

Solid has its particles very close together, so it has a high density and makes it incompressible. In gases, the particles are further apart, so the density is low and it is compressible.

Question 22

How can you determine if something is soluble?

Answer 22

Water is a polar solvent, so substances that are polar or charged will dissolve in it well, but non-polar substances won’t.

Question 23

Which statement about inorganic ionic compounds is always correct
A : dissolve in water to give neutral solutions
B : they release energy when they melt
C : they contain metal cations
D : they form giant structures

Question 24

How does hydrogen bonding occur?

Answer 24

Hydrogen must be bonded to NOF.

Question 25

Explain how the strongest type of intermolecular force in HG arises.

Answer 25

Large difference in electronegativity
F slightly negative and H slightly positive
Attraction between positive H and lone pair on F.

Question 26

Why does CF4 have a bond angle of 109.5°

Answer 26

Around carbon there are 4 bonding pairs of electrons and no lone pairs. Therefore, these repel equally and spread as far apart as possible.