S2.2 The covalent model SL Part 1

Question 1

Octet rule

Answer 1

The tendency of an atom to achieve stability by ensuring its valence shell is full, either by gaining, losing or sharing electrons.

Question 2

Covalent bond

Answer 2

The electrostatic force of attraction between two positive nuclei and a shared pair of electrons.

Question 3

Lewis formula

Answer 3

This shows all valence electrons, whether these are pairs of electrons involved in covalent bonds or non-bonded pairs of electrons, known as non-bonding pairs. Also known as an electron dot or Lewis structure.

Question 4

How do you deduce the Lewis formula for molecules and ions?

Answer 4

Calculate the total number of valence electrons, draw a skeletal structure with single bonds, add non-bonding pairs, and ensure all atoms have a full valence shell.

Question 5

Which molecules are stable with fewer than an octet of electrons?

Answer 5

Molecules like beryllium dichloride (BeCl2) and boron trifluoride (BF3) are stable with incomplete octets by forming the maximum number of covalent bonds.

Question 6

How to name a simple molecular compound from its chemical formula?

Answer 6

Use prefixes (mono-, di-, tri-, etc.) to denote the number of atoms, omitting the prefix for a single atom of the first element listed, unless it’s a single-element compound, which retains the element’s name.

Question 7

How to calculate the total number of valence electrons for molecules and ions with double and triple bonds?

Answer 7

Sum the valence electrons of all atoms present. For ions, add an electron for each negative charge or subtract one for each positive charge.

Question 8

What is the first step in drawing the skeletal structure for Lewis formulas?

Answer 8

Identify the central atom (usually the least electronegative), connect peripheral atoms with single bonds.

Question 9

After connecting atoms with single bonds, what do you do with the remaining electrons?

Answer 9

Distribute them as non-bonding pairs (lone pairs) on the outer atoms to fulfill the octet rule.

Question 10

How are double or triple bonds formed in the Lewis structure?

Answer 10

Use non-bonding pairs from outer atoms to form double or triple bonds with the central atom to complete octets.

Question 11

Final step in deducing the Lewis structure?

Answer 11

Ensure the total number of electrons used matches the calculated number of valence electrons.

Question 12

How does the number of bonds affect bond strength?

Answer 12

More bonds result in stronger bonds. Triple bonds are the strongest, followed by double, then single bonds.

Question 13

Relationship between bond numbers and bond length?

Answer 13

Double and triple bonds are shorter than single bonds due to greater electrostatic attraction pulling nuclei closer.

Question 14

Coordination bonds

Answer 14

A covalent bond where both of the electrons being shared in the bond have been donated by one atom.

Question 15

How can coordination bonds in compounds be identified?

Answer 15

Coordination bonds occur when one atom donates both electrons for a bond, while the other atom accepts them without contributing electrons. They are a special type of covalent bond that differs in the source of electrons.

Question 16

How do coordination bonds form?

Answer 16

Coordination bonds form between a donor species, with non-bonding electrons available for bonding, and an acceptor species that has space to accept electrons. This interaction facilitates stability and adherence to the octet rule.

Question 17

Why are coordination bonds important?

Answer 17

They are crucial for molecules that would not achieve a stable electronic configuration otherwise. Examples include carbon monoxide and complexes involving ammonia and boron trifluoride.

Question 18

How are coordination bonds represented?

Answer 18

They are depicted using Lewis formulas or an arrow notation that indicates electron donation from the donor to the acceptor.

Question 19

Electron domains

Answer 19

The region in which bonding and non-bonding pairs of electrons are most likely to be found. Non-bonding pairs, single bonds, double bonds and triple bonds each count as one electron domain.

Question 20

Electron domain geometry

Answer 20

The region in which bonding and non-bonding pairs of electrons are most likely to be found. Non-bonding pairs, single bonds, double bonds and triple bonds each count as one electron domain.

Question 21

Valence Shell Electron Pair Repulsion (VSEPR)

Answer 21

A theory used to explain and predict molecular geometry, based on number of electron domains (bonded and non-bonded electron pairs).

Question 22

How to predict electron domain and molecular geometry for up to four domains?

Answer 22

Count the electron domains around the central atom: linear (2 domains), trigonal planar (3 domains), tetrahedral (4 domains). Molecular geometry considers atom arrangement, including non-bonding pairs.

Question 23

How do non-bonding pairs and multiple bonds affect bond angles?

Answer 23

Non-bonding pairs are more repulsive, reducing bond angles. Multiple bonds count as one electron domain but affect molecule shape due to electron density.

Question 24

Electronegativity

Answer 24

A measure of how much an atomic nucleus attracts the shared electrons that are involved in a covalent bond.

Question 25

Pauling scale

Answer 25

The scale on which electronegativity is measured, ranging from 0.0 to 4.0 Pauling units.

Question 26

Non-polar bonds

Answer 26

A covalent bond formed between two atoms with equal electronegativity values which results in equal sharing of the electrons in their bond.

Question 27

Polar covalent bond

Answer 27

A bond which has a partially positive end and a partially negative end due to asymmetrical electron distribution caused by the difference in electronegativity of the two bonded species.

Question 28

How does molecular symmetry affect the net dipole moment?

Answer 28

Symmetry plays a crucial role; in asymmetrical molecules with polar bonds, these polarities contribute to a net dipole moment. Conversely, in symmetrical molecules, polarities may cancel out, resulting in no net dipole moment.

Question 29

What initial step is taken to deduce a molecule’s net dipole moment?

Answer 29

The first step involves identifying the presence of polar bonds within the molecule or ion to understand potential contributions to the net dipole moment.

Question 30

What effect does asymmetry have on a molecule’s dipole moment?

Answer 30

Asymmetry in a molecule with polar bonds typically leads to a net dipole moment, indicating distinct positive and negative ends within the molecule.