AQA AS-level Chemistry Topic 1.3 bonding (PT.1)

When forming ionic compounds

Atoms of elements in groups 1, 2 and 3:
-Lose electrons
-Become positive ions

Atoms of elements in groups 5, 6 and 7:
-Gain electrons (e.g. group 6, gain 6 electrons)
-become negative ions

What is the electronic configurations

1s2 2s2 2p6 3s2 3p6 3d10 4s2, 4p6 (but you fill 4s2 before 3d10

What is an orbital?

A region around the nucleus that can hold up to two electrons with opposite spins

What is the shape of a S-orbital

Spherical

What is the shape of a p-orbital

dumbbell shaped

What is the shape of a d-orbital?

four-leaf clover

The number of positive ions the number of positive charges on the ion is equal to:

the group number

Explain what the term oxidizing agent means in terms of electron transfer.

An oxidizing agent accepts electrons from other species

What are the four types of structures

-Giant ionic lattice
-Simple molecular structure
-Giant metallic lattice
-Giant covalent lattice

Giant ionic lattices

-High melting point
-No electrical conductivity (when solid), Electrical conductivity (when liquid or in solution)
-Ionic bonding

Simple molecular Covalent structures

-Low melting point
-No electrical conductivity
-Covalent bonding

Giant metallic lattice

-High melting point
-Electrical conductivity (when solid, even better as a liquid)
-Metallic bonding

What is the order of strength in intermolecular forces
in order of increasing strength

-London forces
-Permanent dipole-dipole interactions
-Hydrogen bonds

Giant Covalent lattice

-High melting point
-No electrical conductivity
-Covalent bonding

Definition of ionic bonding

Electrostatic attraction between positive and negative ions
-Formed between positive metal cations and negative non-metal anions
-found in compounds made up of a metal and a non-metal
-metal forms a positive ion by losing electrons.
Na —> Na+ + e-
-The non-metal forms a negative ion by gaining electrons.
Cl + e- —> Cl-
-The negative ion often has the electron configuration of the next noble gas in the Periodic Table

What is an ionic compound made up of

*positive and negative ions attracted to each other by electrostatic forces.

What do Dot-and-cross diagrams show

The ions in their simplest whole number ratio

A solid ionic compound exists as a ….

Giant ionic lattice

What does giant mean?

Giant means a continuous structure in 3 dimensions

What does a lattice mean?

A Lattice simply means a regular arrangement

Giant ionic lattice arrangement

A Giant ionic lattice is a regular arrangement of oppositely charged ions, held together by electrostatic attractions

melting point of ionic compounds

High

-In order to melt a solid, the attractions within the solid structure must be broken.

-In a giant ionic lattice, these attractions are electrostatic attractions between positive and negative ions

-These electrostatic attractions are generally strong

-The amount of energy required to break them is therefore high

-This results in ionic compounds generally having high melting points

Electrical conductivity of Ionic compounds

-In order for the material to conduct electricity, there must be charged particles able to move freely around the material

-In an ionic compound, these charged particles are ions

-In a solid compound, the ions are fixed in a lattice, so cannot move

-When a molten (melted) or in solution, the structure has broken down and the ions are free to move.

-Ionic compounds CAN therefore conduct electricity when molten or in solution, but NOT when solid

Melting point of Giant Covalent lattices

-In order to melt a solid, the attractions within the solid structure must be broken

-In a giant covalent structure, these attractions are covalent bonds.

-These covalent bonds are generally strong

-The amount of energy required to break them is therefore high

-This results in ionic compounds generally having high melting points

Electrical conductivity of Giant Covalent lattices

-In order for a material to conduct electricity, there must be charged particles able to move freely around the material

-In a covalent compound, these charged particles are electrons

-In a covalent compound, the electrons are fixed in the covalent bonds and cannot move

-Giant covalent compounds cannot therefore conduct electricity

-Graphite is an exception due to its structure. It has delocalised electrons, which can move and it DOES therefore conduct electricity

Ionic bonds form between

Metals and nonmetals

Covalent bonds form between

Non-metals

Metallic bonds form between

metals

Definition of a covalent bond

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

What are lone pairs

Pairs of electrons in the outer shell not involved in bonding

lone pairs must always be shown in dot and cross diagrams

Shared pairs of electrons must always be shown approximately the same distance from each atom.

Bond pairs

pairs of electrons in bonds on the central atom

Why do molecules have 3D shapes?

it's all because of a phenomenon known as Valence Shell Electron Pair repulsion or VSEPR for short

VSEPR tell us…

Valence electrons in bonding pairs and lone pairs repel each other as far apart as possible (largest possible angle between them.)

The greater the number of bonding pairs and lone pairs, the smaller the….

Bond angle

A lone pair of electrons can, in certain circumstances, be used to form…

A dative covalent bond

What is a dative covalent bond?

A shared pair of electrons in which the bonding pair has been provided by one of the bonding atoms only

Each shared electron should be from the bonding atoms

Equidistant

A positive ion will be attracted to any ion

Negative

A negative ion can be bonded to any positive ions if it is close enough

Neighbouring

Definition of covalent bond

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms

A small group of atoms bonded together by covalent bonds is called a _

Molecule

When a covalent bond forms between 2 atoms….

Each atom contributes one electron into the bond. The original source of the two bonding electrons are emphasized by the use of dots and crosses

How to draw a dot-and-cross-diagram for covalent molecules

-Determine how many valence electrons each bonding atom has by using the group number of the periodic table
-Pair up the unpaired electrons between atoms to form covalent bonds

What is the octet rule?

in forming compounds, atoms tend to achieve the electron configuration of a noble gas

Sodium Cyanide, NaCN

-Sodium cyanide has ionic bonding, however the cyanide ion contains two atoms held together by a triple covalent bond

-The electron gained from the sodium gets a different symbol. Gained electrons are never involved in bonding, so will be in a lone pair.

What is the definition of Metallic bonding

The electrostatic attraction between positive metal ions and delocalised electrons

When drawing metallic bonding what must you show?

• a regular lattice (at least 3x3) of metal cations, with GAPS between them, labeled with their charge

-Delocalised electrons between the cations

-Labels: "Lattice of positive _cations" and "delocalised electrons"

¥

diagram for Oxygen

diagram for Nitrogen

N≡N

Carbon dioxide (CO2)

O=C=O

What happens when two atoms form covalent bonds

-unpaired electrons pair up
-the maximum number of electrons that pair up is equal to the number of electrons in the outer shell

How do polar covalent bonds form?

When one of the bonded nuclei has a greater electrostatic attraction for the bonded electrons than the other.

The attractive force of a nucleus on the electrons in a bond is known as its electronegativity.

Little or no difference in electronegativity =

Non-polar covalent bonding

Some difference in electronegativity =

Polar Covalent bonding

A large difference in electronegativity =

Ionic bonding

What are the two types of electron pairs

Bonding pairs and lone pairs

Bonding pairs

A shared pair of electrons is called a bonding pair

Lone pairs

A pair of electrons in the outer shell NOT used in bonding

They can in certain circumstances, be used to form dative covalent bond

Definition of a dative covalent bond

A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only

A dative covalent bond can be written as A—>B with the direction of the arrow indicating the direction in which the electron pair has been donated

What is Average Bond enthalpy

the average enthalpy change which takes place when breaking by homolytic fission one mole of a given type of bond in the molecules of a gaseous species

What is the relationship between average bond enthalpy and the strength of the covalent bond

A stronger bond has a larger average bond enthalpy

how are atoms in a solid metal packed

In an infinite lattice, held together by metallic bonding.

What kind of structure do metals have?

giant

Electrons in metals

-Because metals have relatively low Ionisation energies, the electrons in their outermost shells are held loosely.
-In a metallic solid, each atom loses its valence electrons which then occupy a new set of energy levels extending throughout the lattice.
-These electrons are not associated with any particular atoms but are free to wander through the lattice. They are said to be delocalised

Definition of metallic bonding

The electrostatic attraction between positive metal ions and delocalized electrons

Explain the physical properties of metals

1) High melting and boiling points
Strong electrostatic attraction between positive metal ions and delocalized electrons requires a lot of energy to break

2) Good conductors of electricity when solid or molten
Solid - delocalized electrons can move and carry charge
Molten - delocalised electrons and positive ions can move and carry charge

3) Insoluble in water or non-polar solvents
Strong electrostatic attraction between positive metal ions and delocalized electrons requires a lot of energy to break, which is not available

What are some other characteristics of metals

they are malleable and ductile

Malleable
Can easily be bent in to different shapes because layers of ions can easily slide over each other

Ductile
Can be drawn in to a wire, Because layers of ions can easily slide over each other

What are alloys?

Alloys are mixture of metals, not compounds.

They are used to modify a metal's properties. Frequently they are used to make a metal harder - this is because each metal ion is a slightly different size so layers of ions do not slide over each other so easily

What is the structure of ionic compounds

-The arrangement of the ions in an ionic solid is described as a "giant ionic lattice."0

how can you explain the fact that an ionic compound exists as a giant lattice?

There is a continuous lattice arrangement of + and - ions in three dimensions

What are the physical properties of ionic compounds

1) High melting and boiling points
Strong electrostatic attraction between positive and negative ions needs a lot of energy to overcome

2) Non-conductors of electricity when solid
The ions are fixed in a lattice so cannot move and carry charge

3) Good electrical conductivity when molten or dissolved in water
The ions are no longer fixed in the lattice so are able to move and carry charge

4) Often good solubility in water
Oxygen atoms are attracted to the positive ions in the lattice, and the hydrogen atoms are attracted to the negative ions

5) Brittleness
Due to repulsion of ions

What are the two types of covalent compounds?

Simple molecular and Giant covalent

Definition of simple molecular structure

Small units containing a definite number of atoms with a definite molecular formula

Do simple molecular structures have high or low melting and boiling points

Low

Reason: Weak intermolecular forces between molecules require little energy to break

Are simple molecular structures electrical conductors

No

Reason: There are no free mobile electrons (or other charged particles) to carry charge

Are simple molecular structures soluble in non-polar solvents?

Yes

Reason: Solvent molecules form similar intermolecular bonds with molecules; weak intermolecular forces do not need much energy to overcome

Giant covalent structure definition

Billions of atoms held together to form a network of strong covalent bonds

Do Giant covalent structures have high or low melting and boiling points?

High

reason: Strong covalent bonds need to be broken - needing a lot of energy

Are Giant covalent structures electrical conductors?

No

Reason: No free mobile electrons (or other charged particles) to carry charge

Two examples of giant covalent structures

diamond and graphite

Diamond

-Doesn't conduct electricity (no free electrons to carry charge)

-Hard because the tetrahedral structure of each carbon atom spreads forces h rough the structure. Strong covalent bonds need much more energy to break

Graphite

-An electrical conductor due to the delocalised electrons in layers are free to move and carry charge.

-soft due to weak intermolecular forces between layers can easily be broken and layers can slide over each other

Graphite

-An electrical conductor due to the delocalised electrons in layers are free to move and carry charge.

-soft due to weak intermolecular forces between layers can easily be broken and layers can slide over each other

Diamond and Graphite are of carbon

allotropes

Why does diamond have a very high melting point

Diamond has a giant covalent structure an it requires a lot of energy to break the strong covalent bonds between atoms and melt it

Explain why diamond is used in drill bits

Diamond is very hard because the tetrahedral structure of strong covalent bonds around each carbon atom allows forces to be distributed through the structure