Topic 3 - Chemical Bonding

Question 1

Electronegativity

Answer 1

Is the power of an atom to attract electrons to itself.

Question 2

Ionic Bond

Answer 2

Is an electrostatic attraction between oppositely charged ions.
- This leads to the formation of ionic lattices.

Question 2

Metallic Bond

Answer 2

Is an electrostatic attraction between positive metal ions and delocalised electrons.
- This leads to the formation of metallic lattices.

Question 3

Delocalised Electrons

Answer 3

Are electrons in an atom, ion or molecule not associated with any single atom, or a single covalent bond.
- Metallic lattices and graphite have delocalised electrons.

Question 4

Covalent Bond

Answer 4

Is an electrostatic attraction between the nuclei of two atoms and a shared pair of electrons.
- This leads to the formation of molecules and macromolecules.

Question 5

Co-ordinate (Dative Covalent) Bonds

Answer 5

Type of covalent bond where one atom donates both electrons to the bond. This can only happen between an atom with a lone pair and an atom that is electron deficient.
- This leads to the formation of molecules.

Question 6

Orbital Overlap

Answer 6

Is the connection of orbitals on adjacent atoms in the same regions of space.
- This leads to the formation of bonds in a molecule.

Question 7

δ Bonds

Answer 7

Formed when atomic orbitals overlap linearly along the line joining the two bonded atoms forming molecular orbitals.
- This is the type of bonding in all single covalent bonds.

Question 8

π Bonds

Answer 8

Formed due to the lateral/sideways overlap of two p orbitals, creating electron density above and below the plane of the molecule.
- Double bonds have one π bond and one δ bond.
- Triple bonds have two π bonds and one one δ bond.

Question 9

Hybridisation

Answer 9

Happens when atomic orbitals mix to form new atomic orbitals. The new orbitals have the same total electron capacity as the old ones. The properties and energies of the new, hybridized orbitals are an ‘average’ of the original unhybridized orbitals.

Question 10

Bond Energy

Answer 10

The energy required to break one mole of a particular covalent bond in the gaseous state.

Question 11

Bond Length

Answer 11

Is the internuclear distance of two covalently bonded atoms.
- In general, the longer the bond is, the weaker the bond is.

Question 12

VSEPRT

Answer 12

States that the electron pairs around the central atom in a molecule take up positions as far from one another as possible in order to minimise their electrostatic repulsions. The repulsion between lone pairs is greater than the repulsion between bonding pairs.
- This is used to predict molecule shapes.

Question 13

Intermolecular Forces

Answer 13

Of attraction, or repulsion, act between molecules and other types of neighbouring particles, such as other molecules, atoms or ions.
- There are four types
1. hydrogen bonding
2. van der Waals’
3. permanent and instantaneous dipole interactions
4. ion-dipole interactions

Question 14

Hydrogen Bonds

Answer 14

An electrostatic force of attraction between a hydrogen atom covalently bonded to an atom of either fluorine, oxygen or nitrogen in one molecule and a fluorine, oxygen or nitrogen atom of another molecule.

Question 15

Bond Polarity

Answer 15

Occurs when two bonded atoms unequally share electrons, due to differences in electronegativity. The unequal sharing of electrons within a bond leads to one end of the bond becoming more positive and the other more negative.

Question 16

Dipoles

Answer 16

Occur when a positive and a negative charge are separated by some fixed distance.
- Such as a molecule with a positive charge at one end and a negative at the other.

Question 17

Dipole Moment

Answer 17

Is the measure of the net polarity of a molecule.
- Molecules with a greater difference in electronegatives will have a greater dipole moment (unless they are symmetrical).

Question 18

Permanent Dipoles

Answer 18

Occur when two atoms in a molecule have substantially different electronegativity: one atom attracts the bond pair electrons more than another, becoming more negative, while the other atom becomes more positive. A molecule with a permanent dipole moment is called a polar molecule.

Question 19

Instantaneous Dipoles

Answer 19

Simultaneously form in a non-polar molecule due to chance when electrons happen to be more concentrated in one place than another in a molecule, creating a temporary dipole.
- These dipoles are temporary and weaker in effect than permanent dipoles.

Question 20

Induced Dipoles

Answer 20

Occur when a polar molecule induces a dipole in an atom, or in a non-polar molecule, by disturbing the arrangement of electrons in the non-polar species.
- This is when a non-polar molecule, or atom, temporarily gains polarity from a close-by polar molecule or ion. The polarity is lost when the polar molecule or ion moves away.

Question 21

Non-polar Molecules

Answer 21

Are molecules in which the electrons are shared equally between the nuclei. As a result, the distribution of charge is even and the force of attraction between different molecules is small. Non-polar molecules show little reactivity.
- This happens either when the molecule has no bond polarity or has bond polarity, but the molecule is symmetrical.

Question 22

Polar Molecules

Answer 22

Have a partial positive charge in one part of the molecule and a complementary negative charge in another part.
- This arises from a difference in electronegativities in the atoms in the molecule.

Question 23

Polarising Power

Answer 23

Is the ability of a cation to distort the electron cloud around an anion.

Question 24

Polarisability

Answer 24

Is a measure of the degree to which an atom, or ion, has had its electron cloud distorted.

Question 25

Dimers

Answer 25

Are molecules or molecular complexes consisting of two identical molecules linked together.
- Example aluminium chloride forms a dimer, Al2Cl6.