Topic 4: Chemical bonding and structure

Question 1

How are ions formed

Answer 1

Ions are formed when one or more electrons are transferred from one atom to another

Question 2

Why do ions form

Answer 2

Ions form in order to gain a full outer shell (so have to lose or gain electrons)

Question 3

Cations and anions

Answer 3

Cations are positively charged (metals)
Anions are negatively charged (non-metals)

Question 4

Structure of ionic compounds

Answer 4

Ionic compounds are typically solids and have lattice-type structures that consist of repeating cations and anions

Question 5

Physical properties of ionic compounds

Answer 5

• Ionic compounds have strong electrostatic forces therefore have low volatility
• Ionic compounds in their solid state cannot conduct electricity (because the ions cannot move so cant carry a charge). However, when they are molten or aqueous they can
• Ionic compounds dissolve in polar solvents such as water. THis is because the polar solvents are attracted to the ions in the lattice (ions are pulled from the lattice)

Question 6

How are covalent bonds formed

Answer 6

Covalent bonds are formed between two non metals (formed by electrostatic attraction between a shared pair of electrons and positive nuclei)

They share electrons in order to achieve full outer shell

Question 7

Single, double, triple covalent bond

Answer 7

Covalent bonds can take the form of single bonds, double bonds, or triple bonds

Single bonds can be seen in F2
Double bonds in O2
Triple bonds in N2

Question 8

Covalent bond strength and length

Answer 8

Strength= T>D>S
Length= S>D>T

Question 9

Octet rule

Answer 9

States that elements tend to lose electrons, or gain electrons, or share electrons in order to acquire a full outer shell

Question 10

VSEPR theory

Answer 10

Since electrons are negatively charged subatomic particles, pairs of electrons repel one another to be as far apart as possible in space

Question 11

Electron domain geometry

Answer 11

Based on the total number of electron domains (every pair of electrons occupy an electron domain)

Question 12

Molecular geometry

Answer 12

Gives the shape of a molecule

Question 13

VSEPR: 2 electron domains

Answer 13

Linear 180 degress

Question 14

VSEPR: 3 electron domains

Answer 14

Trigonal planar 120 degrees
Bent Less than 120 degrees

Question 15

VSEPR: 4 electron domains

Answer 15

Tetrahedral 109.5 degrees
Trigonal pyramidal less than 109.5 degrees
Bent less than 109.5 degrees

Question 16

Resonance structures

Answer 16

This occurs when there is more than one possible arrangement for a double bond in a molecule.

These multiple possible arrangements contribute to an overall structure called resonance forms.

The actual electronic structure of the species is called a resonance hybrid of these forms

In order to show the idea of resonance, the contributing resonance forms are linked via a double arrow

Example of resonance is benzene C6H6 which forms a delocalized benzene ring

Question 17

Molecular polarity

Answer 17

If there are non-polar bonds, the molecule is non polar
If there are polar bonds and molecule is symmetrical, molecule is non polar
If there are polar bonds and molecule is asymmetrical, molecule is polar

Question 18

Allotropes

Answer 18

Allotropes are structures of the same element that can vary in both chemical and physical properties
Carbon has 4 allotropesL graphite, diamond graphene, c60 fullerene

Question 19

Silicon dioxide

Answer 19

Most commonly in the form of quartz. An example of a three-dimensional covalent network solid

Question 20

Coordinate covalent bonding

Answer 20

A covalent bond in which the pair of electrons comes from only 1 of the atoms (e.g [NH4]+ )

Question 21

Simple covalent structures

Answer 21

These contain only a few atoms held together by strong covalent bonds (e.g carbon dioxide)

These have low boiling points and are usually liquid and gases, due to the weak intermolecular forces

Non conductive because they do not have any free electrons or an overall electric charge

Question 22

Giant covalent structures

Answer 22

Contain a lot of non-metal atoms each joined to adjacent atoms by covalent bonds - e.g silicon dioxide

These are very strong because there are many bonds involved

High melting points because a lot of strong covalent bonds must be broken

Some are conductive as some have free electrons whilst others do not

Question 23

Graphite

Answer 23

Graphite has a hexagonal layer structure. It has covalent bonds between the carbon atoms however has weak van der wall forces between the layers themselves- allowing the bonds to be overcome very easily. This means that they layers can slide over eachother.

Graphite has good conductivity as it contains delocalized electrons between its layers (with the electrons moving through the layers)

Question 24

Diamond

Answer 24

In diamond. each carbon atom is joined to four other carbon atoms in a tetrahedral arrangement. Diamond is very hard and has a high melting point. Diamond is a bad conductor as there are no delocalized electrons as the outer shell electrons are used for covalent bonds

Question 25

C60 fullerenes

Answer 25

60 carbon atoms form a sphere in which each atom is covalently bonded to three others. Fullerene is a semiconductor that is very strong and light. It is used in the medical field for the transportation of medicines in the body.

NOT A LATTICE

Question 26

Silicon

Answer 26

A member of group 4 and so is able to form 4 covalent bonds to other silicone atoms to form network covalent structure

Question 27

Intermolecular forces

Answer 27

The forces that exist between molecules

There are three main types of intermolecular forces

Question 28

Intramolecular forces

Answer 28

Forces that exist between ATOMS (ionic and covalent)

Question 29

London dispersion forces

Answer 29

The weakest intermolecular force.

A temporary attractive force that results when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles.

London dispersion forces are the attractive forces that cause non-polar substances to condense to liquids and to freeze into solids when the temperature is lowered sufficiently

Question 30

Dipole-dipole

Answer 30

A dipole is a molecule that has both positive and negative regions

A dipole dipole force is when the positive side of a polar molecule attracts the negative side of another polar molecule

The strength of this attraction with depend on the distance and orientation of the dipoles

The molecules need to be very close to eachother like a liquid in order to work

Question 31

Hydrogen bonds

Answer 31

A hydrogen bond is an attraction between a slightly positive hydrogen on one molecule and a slightly negative atom on another molecule

Hydrogen bonds are a type of dipole-dipole force

The large electronegative difference between hydrogen atoms and fluorine, oxygen, and nitrogen causes hydrogen bonds to be the strongest of all intermolecular forces

Question 32

Strengths of intermolecular forces

Answer 32

London dispersion forces < dipole-dipole forces < hydrogen bonds

Question 33

Metallic bonding

Answer 33

A metallic bond is the electrostatic attraction between positive metal ions and delocalized electrons

Question 34

Properties of metals

Answer 34

• Metals conduct electricity because they have a sea of delocalized electrons. This means that the electrons can move freely and therefore can carry a charge.
• Metals are malleable (change shape when a force is applied) and ductile (can be drawn into wires). This is because the layers can slide over eachother.
• Shiny

Question 35

Alloys

Answer 35

Alloys are the result of melting and mixing different metals together in order to create a material with enhanced properties.

This is done by adding mixing amounts of various metals in order to achieve certain characteristics.

The production of alloys is possible because of the non-directional nature of the delocalized electrons, and the fact that the lattice can accommodate ions of different sizes.

Alloys are usually more stronger than regular metals. This is because if different atoms are present, the regular network of positive ions will be disturbed. The atoms of a different size also makes it harder for layers of positive ions to slide over eachother and therefore prevent bending or denting of the metal.