Topic 2 Bonding and structure

Question 1

Dative covalent bonding

Answer 1

A dative (or coordinate) covalent bond is formed when an empty orbital atom overlaps with an orbital containing a lone pair of electrons of another atom.

Question 2

VESPR theory

Answer 2

The shape of a molecule is caused by the repulsion between the pairs of electrons, both bonded and lone pairs.
Highest repulsion: lone pair-lone pair
Middle repulsion: lone pair-bonding pair
Least repulsion: bonding pair-bonding pair

Question 3

Polarity explanation

Answer 3

The drift of bonded electrons towards the more electronegative element results in a separation of charge. This separation of charge is called a dipole.

Question 4

Individual dipoles

Answer 4

Individual dipole can either reinforce one another or cancel each other out.
-If cancelled: the resulting molecule will have no overall dipole and is said to be ‘non-polar’
-If reinforced: the molecule will possess an overall dipole and it is said to be ‘polar’.

Question 5

Polarity in diatomic molecules

Answer 5

Some diatomic molecules are non-polar if the two atoms have the same electronegativity.
The distribution of electron density is symmetrical.
Diatomic molecules that are polar means the electronegativity of one element is greater than the other.

Question 6

Bonding within molecules

Answer 6

-Bonding within molecules (intramolecular) is strong
-Bonding between molecules (intermolecular) is weak
-Molecules and monatomic noble gases are subject to weak attracting forces.

Question 7

Permanent dipole

Answer 7

Permanent dipole-dipole are the weak intermolecular forces of attraction between permanently polar molecules.
-consists of regions of partial positive charge and partial negative charge
-more energy is needed to separate the molecules; higher boiling points.
(These occur when two atoms in a molecule have substantially different electronegativity: One atom attracts 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 8

Instantaneous/induced dipole interactions

Answer 8

Electrons in atoms or molecules are moving at high speed in orbitals.
A dipole forms when one side is slightly negative and the other slightly positive (electrons on one side of an atom).
The dipole can then induce a dipole in a neighbouring molecule.
The greater the number of electrons, the stronger the attraction.

Question 9

Hydrogen bonding

Answer 9

When hydrogen bonded to a highly electronegative atom, the bonding electron pair is drawn towards the electronegative atom.
Hydrogen has no inner shell electron so the nucleus is exposed to attraction by nearby electron cloud, a lone pair of electrons of the electronegative atom.

Question 10

Hydrogen bonding pt 2

Answer 10

A hydrogen atom must be directly bonded to a highly electronegative atom (F, O, N)
An unbounded pair of electrons is presented on the electronegative.
-Hydrogen fluoride
-Water
-Ammonia
-Methanol
Can form 4 bonds.

Question 11

Hydrogen bonding pt 3 (types of hydrogen bonding)

Answer 11

Intermolecular hydrogen bond:
-Hydrogen bond formed between two molecules
Intramolecular hydrogen bond:
-Hydrogen bonds formed between two different atoms in the same molecule.
(Intermolecular hydrogen bond is stronger than Van Der Waal’s forces)

Question 12

Electrostatic attraction

Answer 12

Electrostatic attraction between hydrogen atoms bonded to small strongly electronegative atoms and the lone pair electrons on these electronegative atoms
(when negatively charged atom is attracted towards positively charged atom).

Question 13

Why do metallic structures have a high melting point?

Answer 13

Strong intramolecular forces between cations and electrons which needs high energy to break.

Question 14

Why do metallic structures conduct electricity?

Answer 14

When the delocalised electrons move, they carry a current.

Question 15

Why do metallic structures have high malleability?

Answer 15

In regular arrangement of lattices which move the layers with stress.

Question 16

Ionic properties: states

Answer 16

Ionic compounds are solid at room temperature because it takes a lot of energy to break the electrostatic bonds between the positive ions and the negative ions.

Question 17

Ionic properties: conductivity

Answer 17

They conduct when molten because of the free moving ions that can collect the current.

Question 18

Ionic properties: solubility

Answer 18

Soluble in water as the energy required to break the lattice structure can be supplied by hydration of the separate ions.

Question 19

Isoelectric

Answer 19

Two atoms or ions or molecules that have the same electronic structure and the same number of valence electrons (outermost electrons).
The term means ‘equal electric’ or ‘equal charge’
Isoelectric chemical species typically display similar chemical properties.

Question 20

Sigma (σ) bonds

Answer 20

-Comes from the greek letter for S
-Single bonds
-Bonds are symmetrical and in line with the nucleus
-Form single covalent bonds.

Question 21

Pi (π) bonds

Answer 21

-Comes the greek letter for p
-Double and triple bonds
-Need to form on sigma bond before forming pi bonds
-Bonds are non-symmetrical and not in line with the nucleus
Form double and triple covalent bonds.

Question 22

Strength of a bond due to atomic radius

Answer 22

-The larger the atomic radius, the longer/weaker bond
-This is due to more shielding and outer electrons are further from the positive nucleus
-More bonds=stronger bonds
-This is due to having more bonds to break.

Question 23

Electronegativity definition

Answer 23

Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons in a covalent bond.

Question 24

Factors affecting electronegativity

Answer 24

-Atomic radius
-Electron sheilding
-Nuclear charge

Question 25

Electronegativity across a period

Answer 25

Electronegativity across a period increases.
The nuclear charge increases, but the number of shielding electrons remain constant, so the attraction to the shared pair increases.
Atomic number increases-more protons/electrons, bigger nuclear charge.

Question 26

Electronegativity down a group

Answer 26

Electronegativity down a group decreases.
Nuclear charge increases, however there is an increase in the number of shielding electrons and the shared pair is further from the nucleus so is attracted less strongly.

Question 27

Bonding linked to electronegativity

Answer 27

No difference in electronegativity= non polar covalent bond.
Small difference in electronegativity= polar covalent bond.
Large difference in electronegativity= ionic bond.