Weeks 6 & 7 - Covalent Bonds, Lewis Structures and Gases

Question 1

What is a covalent bond?

Answer 1

The sharing of electron pairs between atoms (sharing 2).

Question 2

What is a double bond?

Answer 2

A chemical bond in which 2 pairs (4) of electrons are shared between two atoms.

Question 3

What is a triple bond?

Answer 3

A chemical bond in which 3 pairs (6) of electrons are shared between two atoms.

Question 4

Define electronegativity.

Answer 4

Ability of an atom in a molecule to attract the shared electrons in a chemical bond.

Question 5

Describe what is meant by bond length.

Answer 5

In molecular geometry, bond length is the average distance between the nuclei of two bonded atoms in a molecule.

Question 6

What is an ionic bond?

Answer 6

Electrostatic attraction between oppositely charged ions. Cations (lose electrons) transfer their electrons to the anions (gain electrons).
Cations carry a positive charge and anions carry the negative charge.

Question 7

What is bond strength/ energy?

Answer 7

The energy required to break the bond - always positive.
Used to indicate how stable a compound is or how easily it can break a particular bond.
More energy = more stable bond.

Question 8

What is polarity?

Answer 8

Polarity is a separation of electric charge leading to a molecule or its chemical groups having an electrical dipole moment.
Molecular polarity is dependant on the difference in electronegativity between atoms in a compound and the asymmetry of the compounds structure.

Question 9

What is the octet rule?

Answer 9

Is a chemical rule of thumb that reflects the observation that atoms of the main group elements tend to combine in such a way that each atom has 8 electrons in its valence shell.

Question 10

What is resonance?

Answer 10

1 or 2 or more Lewis structures for the same molecule.

Question 11

What is a dipole moment?

Answer 11

Most chemical bonds are polar - one end of the bond is slightly positive and one end is slightly negative.
Bond polarities can lead to this - a molecule with this type of electron density distribution = dipole moment.
The more polar the bond, the larger the dipole moment.

Question 12

What is pressure?

Answer 12

Force per unit area.

How often and how hard gas molecules collide with the container wall.

Question 13

What is a barometer?

Answer 13

An instrument for measuring atmospheric pressure

Question 14

Boyle’s law is?

Answer 14

The pressure of gas is inversely proportional in its volume.
E.g if pressure decreases, volume increases and vice versa.

Question 15

What is the gas constant?

Answer 15

The proportionality constant used in the ideal gas equation - defined as R= 8.314 J mol-1 K-1

Question 16

What is the ideal gas equation?

Answer 16

The equation describing the behaviour of an ideal gas.

Denoted as pV=nRT

Question 17

What is dalton’ gas law?

Answer 17

Temperature is directly proportional to it volume and pressure.
E.g low temperature = low volume & low pressure and vice versa

Question 18

What is partial pressure?

Answer 18

The pressure exerted by a single gas in a mixture of gases.

Question 19

Define what avogadro’s gas law is?

Answer 19

The amount of volume of gas is directly proportional to the number of moles of the gas.
E.g increased volume = increased moles

Question 20

What is STP?

Answer 20

Standard temperature and pressure - temperate = 0 degrees C and pressure is at 1 atmosphere.

Question 21

1 atmosphere is equal to?

Answer 21

760mm Hg

Question 22

Experiments show that at STP, 1 mole of an ideal gas occupies what?

Answer 22

22.414 L

The type of gas makes no difference to this figure. ONLY for an ideal gas

Question 23

Name some of the ideal gas properties.

Answer 23

A hypothetical gas whose P, V and T behaviours can be completely accounted for by the ideal gas equation.

. Molecules don’t repel or attract each other
. Their volume is negligible compared with the volume of the container
. Don’t really exist

Question 24

What is the kinetic molecular theory of gases?

Answer 24

1. A gas is composed of molecules that are separated from each other by distances far greater than their own dimensions - considered points, that is they have mass but negligible volume.
2. Gas molecules are in constant motion, in random directions. Collisions are perfectly elastic.
3. Exert neither attractive nor repulsive forces on one another
4. Average kinetic energy is proportional to the temp @ kelvin. 2 gases at the same temp = same kinetic energy

Question 25

What is gas diffusion?

Answer 25

The spread of one substance throughout a space or throughout a second substance.

Question 26

What is gas effusion?

Answer 26

The escape of gas molecule through a tiny hole into an evacuated space.