Module 2.2 - Electrons, Bonding and Structure.

Question 1

What is an orbital?

Answer 1

A region around the nucleus that can hold up to two electrons, with opposite spins. Orbitals within the same sub-shell have the same energy.

Question 2

What is ‘spin-pairing’?

Answer 2

If there are two electrons in an orbital, they have to ‘spin’ in opposite directions.

Question 3

What shape are s orbitals?

Answer 3

Spherical.

Question 4

What shape are p orbitals?

Answer 4

Dumbbell shapes.

Question 5

How are ions formed?

Answer 5

Ions are formed when electrons are transferred from one atom to another to gain a full outer shells. They may be positively or negatively charged.

Question 6

What is an ionic bond?

Answer 6

An ionic bond is an electrostatic attraction between two oppositely charged ions.

Question 7

Describe a giant ionic lattice structure?

Answer 7

The ions are packed together alternately in a regular and repetitive structure called a lattice. It’s ‘giant’ because it’s made of the same basic unit repeated over and over again. It forms because each ion is electrostatically attracted in all directions to ions of opposite charges. They normally have very high melting points because it requires lots of energy to break these strong ionic bonds.

Question 8

What are three main properties of ionic compounds?

Answer 8

> Ionic compounds conduct electricity when they’re molten or dissolved, but not as solids.
Have high melting and boiling points.
Tend to dissolve in water.

Question 9

Why do ionic compounds tend to dissolve in water?

Answer 9

Water molecules are polar, so the delta positive and delta negative parts of the molecules are attracted to the charged ions and pull these ions away from the lattice and cause it to dissolve.

Question 10

What does average bond enthalpy mean?

Answer 10

Measures the energy required to break a covalent bond.

Question 11

What is dative covalent bonding?

Answer 11

Where both electrons are shared from one atom.

Question 12

What is a covalent bond?

Answer 12

A shared pair of electrons.

Question 13

What is ‘electron pair repulsion theory’?

Answer 13

Electrons are all negatively charged, so electrons will repel each other as much as they can The type of electron pairs (lone pairs/bonding pairs) affects how much it repels other electron pairs.

Question 14

Which molecular shape has an 180 degree angle around the central atom?

Answer 14

Linear.

Question 15

What is another name for the molecule shape non-linear and what is it’s bond angle?

Answer 15

Angular and 104.5 degrees.

Question 16

What shape has 3 electron pairs around the central atom with no lone pairs and what bond angle would it have?

Answer 16

Trigonal planar and 120 degrees.

Question 17

What shape would a triogonal planar be if you added a lone pair and what bond angle would it have?

Answer 17

Triogonal pyramidal and 107 degrees.

Question 18

What bond angle does a tetrahedral shaped molecule have between its 4 electron pairs?

Answer 18

109.5 degrees.

Question 19

What is the most electronegative element?

Answer 19

Fluorine.

Question 20

Name three other very strongly electronegative elements?

Answer 20

Oxygen, nitrogen and chlorine.

Question 21

In covalent bonds what causes a permanent dipole?

Answer 21

Between two atoms of different electronegativities, the bonding electrons are pulled towards the more electronegative atoms, making the bond polar. In a polar bond, the difference in electronegativity between the two atoms causes a permanent dipole.

Question 22

What is a dipole?

Answer 22

A dipole is a difference in charge between the two atoms caused by a shift in electron density in the bond.

Question 23

Why are the covalent bonds in diatomic gases non-polar?

Answer 23

Because the atoms have equal electronegativities and so the electrons are equally attracted to both nuclei.

Question 24

Polar bonds have permanent dipoles however the arrangement of polar bonds in a molecule determines whether it has an overall dipole. Explain this.

Answer 24

If the polar bonds are arranged symmetrically so that the dipoles cancel each other out, then the molecule has no overall dipole and is non-polar. But, if the polar bonds are arranged so that they don’t cancel each other out, their charge is arranged unevenly across the whole molecule so will have an overall dipole. Molecules with an overall dipole are polar.

Question 25

Are intermolecular forces stronger or weaker than covalent, ionic, metallic bonds?

Answer 25

Weaker.

Question 26

What are the three types of intermolecular forces you need to know?

Answer 26

> Induced dipole-dipole forces
Permanent dipole interactions
Hydrogen bonding (the strongest type).

Question 27

Why are induced dipole-dipole forces found between all atoms and molecules?

Answer 27

Electrons in charge clouds are always moving very quickly. At any particular moment, the electrons are likely to be more to one side than the other and at this moment the atom would have a temporary dipole. The dipole can cause another temporary (induced) dipole in the opposite direction on a neighbouring atom, the two dipoles are then attracted to each other. The second dipole can cause yet another dipole etc. Because the electrons are constantly moving the dipoles are being created and destroyed all the time. Even though the dipoles keep changing, the overall effect is for the atoms to be attracted to each other.

Question 28

What affects the strength of an induced dipole-dipole?

Answer 28

> Larger molecules - have larger electron clouds meaning stronger induced dipole-dipole forces.
Greater surface area - bigger exposed electron cloud so stronger induced dipole-dipole.

Question 29

Describe the trend of induced dipole-dipole forces?

Answer 29

As you go down the group, the induced dipole-dipole forces (and the boiling points) increase because the number of shells of electrons increases and so atomic molecular size increases.

Question 30

Describe the induced dipole-dipole forces that are responsible for holding iodine molecules together in a lattice?

Answer 30

Iodine atoms are held together in pairs by strong covalent bonds to form molecules. These molecules are then held together in a molecular lattice arrangement by weak induced dipole-dipole attractions.

Question 31

Describe permanent dipole-dipole interactions?

Answer 31

They are present in polar molecules. The delta + and delta - charges on polar molecules cause weak electrostatic forces of attraction between molecules. These are permanent dipole-dipole interactions. Permanent d-d interactions happen in addition to induced d-d interactions.

Question 32

When can hydrogen bonding occur and explain?

Answer 32

Can only happen when hydrogen is covalently bonded to fluorine, nitrogen or oxygen for hydrogen has a high charge density because its so small, and F, N and O are very electronegative. The bond is so polarised that a weak bond form between the H of one molecule and a lone pair of electrons on the F, N and O in another molecule.

Question 33

How does hydrogen bonding affect the properties of substances?

Answer 33

> Soluble in water.

>Have higher boiling and freezing points than molecules that are of a similar size that are unable to form H bonds.

Question 34

List 3 behaviours of simple covalent compounds due to intermolecular forces?

Answer 34

> Low melting and boiling points.
Polar molecules are soluble in water.
Simple covalent compounds don’t conduct electricity.

Question 35

What are the four different type of orbital?

Answer 35

s, p, d and f.

Question 36

What is the definition of an acid?

Answer 36

It releases H+ ions in aqueous solution.