Chemistry: Topic 2: Bonding, structure, and the properties of matter

What are the three types of strong chemical bonds?

• Ionic

• Covalent

• Metallic

What are the particles like in ionic bonding?

Oppositely charged ions

What are the particles like in covalent bonding?

Atoms which share pairs of electrons

What are the particles like in metallic bonding?

Atoms which share delocalised electrons

What does ionic bonding occur in?

Compounds formed from metals combined with non-metals

What does covalent bonding occur in?

Compounds of non-metals

What does metallic bonding occur in?

Metallic elements and alloys

What is an ion?

A charged particle

What type of ions do groups 1 and 2 form?

positive (cations)

What type of ions do groups 6 and 7 form?

negative (anions)

Give the ions formed by elements in each group

• Group 1 = 1+ ion

• Group 2 = 2+ ion

• Group 3 = 3+ ion

• Group 4 = 4+or 4- ion

• Group 5 = 3- ion

• Group 6 = 2- ion

• Group 7 = 1- ion

What happens when a metal atom reacts with a non-metal atom?

Electrons in the outer shell of the metal atom are transferred

Describe how an ionic bond forms

• The metal atom loses electrons to become a positively charged ion

• The non-metal atom gains these electrons to become a negatively charged ion

• They have opposite charges to they are strongly attracted to one another by electronic forces

What bonding is there in sodium chloride (NaCl)?

Ionic

Describe the ionic bonding of sodium chloride

• The sodium atom gives up its outer electron, becoming an Na⁺ ion

• The chlorine atom picks up the electron becoming a Cl^- ion

• The Na⁺ and Cl^- ions are attracted together as they have opposite charges

Why are the ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 like?

They have the electronic structure of a noble gas (full outer shells)

What does the charge on the ions produced by metals in Groups 1 and 2 and by non-metals in Groups 6 and 7 relate to?

The group number of the element in the periodic table

Describe how Potassium forms an ionic compound with an ion of sulfur

• electrons transferred from potassium to sulfur

• two potassium atoms each lose one electron

• forming K⁺ / 1+ ions

• sulfur atoms gain 2 electrons

• forming S²⁻ / 2− ions

How can the electron transfer during the formation of an ionic compound be represented?

By a dot and cross diagram

Why are dot and cross diagrams useful?

• show the arrangement of electrons

• shows where each electron came from

Why are dot and cross diagrams not useful?

• they don’t show the structure of the compound

• don’t show the size of the ions

• don’t show how they’re arranged

What structure do ionic compounds have?

Regular giant ionic lattice structures

What are ionic compounds held togther by?

• Strong electrostatic forces of attraction between oppositely charged ions

• These forces act in all directions in the lattice

What is the 3D balls model of ionic compounds like?

• Shows the relative sizes of the atoms

• Shows the regular pattern of an ionic crystal

• Only lets you see the outer layer of the compound

What is the ball and stick model of ionic compounds like?

• Shows regular pattern of an ionic crystal

• Shows how all ions are arranged

• Suggests the compound extends beyond what is shown

• Isn’t to scale, so the relative sizes of the atoms may not be shown

• In reality, there are no gaps/ visible bonds between the ions

What are the properties of ionic compounds?

• High MP and BP

• Can’t conduct electricity when solid, but can when molten or aqueous

Why do ionic compounds have high MP and BPs?

• There are many strong bonds between the ions

• It takes a large amounts of energy needed to break the many strong bonds

Why can ionic compounds not conduct electricity when solid?

The ions are held in place, so electrons cannot move to carry an electric charge

Why can ionic compounds conduct electricity when molten or aqueous?

• When melted, the ions are free to move so a charge can flow

• When dissolved, the ions separate and are free to move in the solution, letting them carry an electric charge

How do you work out the empirical formula of an ionic compound from a diagram?

• Dot and cross diagram - count how many atoms there are of each element

• 3D diagrams - work out the ions and charges, then balance them so the overall charge of the compound is 0

What are the complex molecular cations?

• Ammonium - NH₄⁺

What are the complex molecular anions?

• Hydroxide - OH^-

• Nitrate - NO₃^-

• Carbonate - CO₃^2-

• Sulfate - SO₄^2-

How does a covalent bond form?

When two non-metal atoms share pairs of covalent bonds

Why are covalent bonds so strong?

The positively charged nuclei of the bonded atoms are attracted to the shared pair by electrostatic forces

What might covalently bonded substances consist of?

Small molecules

Which electrons do atoms share in covalent bonds?

Those on the outer shell (as this is where the highest energy levels are)

How many extra electrons does each single covalent bond provide for each atom

1

Why do atoms bond covalently?

To get a full outer shell, which gives it a stable structure

Dot and cross diagrams for covalent bonds:

• What do they look like?

• Why are/ aren’t they useful?

• Only draw outer shell

• Electrons drawn in the overlap between the shells are shared

• Useful for showing which atoms in a covalent bond come from

• Don’t show the relative sizes of the atoms

• Don’t show how the atoms are arranged in space

Displayed formula diagrams for covalent bonds:

• What do they look like?

• Why are/ aren’t they useful?

• Shows the covalent bonds as single lines between atoms

• - shows a single bond, = shows a double bond and so on

• Useful to show how atoms are connected in large molecules

• Doesn't show the 3D structure of the molecule

• Doesn’t show which atoms the electrons in the covalent bond have come from

3D model for covalent bonds:

• What do they look like?

• Why are/ aren’t they useful?

• Shows the atoms, the covalent bonds and their arrangement in space next to each other

• Can get confusing for large molecules where there are lots of atoms to include

• Don't show where the electrons in the bonds have come from 

How do you find the empirical formula of the covalently bonded compound from these diagrams?

Count the number of each element

How is ammonia different to ammonium?

• Ammonia - NH₃

  • the nitrogen needs to gain 3 electrons and the hydrogen only 1

  • they form 3 single covalent bonds

• Ammonium - NH₄

  • same thing happens, but a 4th hydrogen loses its only electron to the surroundings

  • it needs 2 more electrons for a full outer shell

  • it shares nitrogen’s final two electrons to do this

What are the properties of simple molecular substances?

• low MPs and BPs

• mostly gases at room temp

• don’t conduct electricity

• bigger simple molecular substances have higher MP and BPs

What are IMFs?

Intermolecular forces

What are the electrostatic forces?

Attraction + repulsion

Why do simple molecular substances have low MP and BPs?

There are weak IMFs between the molecules

Why do larger simple molecular structures have higher MPs and BPs?

The IMFs increase with the size of the molecules

Why don’t simple molecular substances conduct electricity?

The molecules do not have an overall electric charge

Give an example of a covalently bonded substance with large molecules

Polymers

What are polymers?

Long chains of repeating units

How are polymers formed?

• Lots of small units are linked together to form a long molecule that has repeating sections

• The atoms are linked to other atoms by strong covalent bonds

How do you draw the displayed formula of a polymer?

• N is the number of times the section repeats

• the repeating unit is in the brackets

• the bonds on the outside are both in and out of the brackets

What are the properties of polymers?

• Strong IMFs, so have high MPs and BPs

• Solid at room temp

• IMFs are still weaker than ionic or covalent bonds, so have lower MPs and BPs than ionic or giant molecular compounds

What are macromolecules?

Giant covalent molecules

What are the properties of giant covalent structures?

• High MPs and BPs

• Solids

• Don’t conduct electricity (even when molten) due to no charged particles

Why do giant covalent structures have high MP and BPs?

• no IMFs, only covalent bonds

• these require lots of energy to break

Give 3 examples of covalently bonded substances that have giant covalent structures

• diamond

• graphite

• silicon dioxide (silica - what sand is made of)

What do metals consist of?

Giant structures of atoms arranged in a regular pattern

How are metallic bonds formed?

• The electrons in the outer shell of metal atoms are delocalised and so are free to move through the whole structure

• This creates positively ionic metals

• The electrostatic forces of attraction are between the positive metal ions and delocalised electrons

Diagram of metallic bonding

What are the MP and BPs of metals like?

Mostly high due to strong metallic bonds

How are atoms arranged in pure metals?

In layers

What do the layers of atoms in metals allow for?

Can be bent and shaped as the layers can slide over each other

Why are alloys used more often than pure metals?

• Pure metals are too soft for many uses

• Mixing them with other metals to create alloys makes them harder

Why are alloys harder than pure metals?

• The atoms are different sizes, so the layers are distorted

• this means the layers can slide over each other less easily

Why are metals good conductors of electricity?

The delocalised electrons in the metal carry electrical charge through the metal

Why are metals good conductors of thermal energy?

Energy is transferred by the delocalised electrons

What are the three states of matter?

• solid

• liquid

• gas

What takes place at melting point?

melting and freezing

What takes place a boiling point?

boiling and condensing

Particle model of the three states of matter

What does the amount of energy needed to change state from solid to liquid and liquid to gas depend on?

The strength of the forces between the particles of the substance

What does the nature of the particles involved depend on?

The type of bonding and the structure of the substance

How do the strength of the forces between particles affect the MP and BP?

The stronger the forces between the particles the higher the MP and BP

What are the limitations of the solid sphere particle model?

• There are no forces

• Particles are represented as spheres

• The spheres are solid and inelastic

What are the state symbols for chemical equations?

• solid (s)

• liquid (l)

• gas (g)

• aqueous (aq)

Give 4 allotropes of carbon

• diamond

• graphite

• graphene

• the fullerenes

Describe the structure of diamond

• each carbon forms 4 covalent bonds with other carbon atoms

• giant covalent structure

What are the properties of diamond?

• Hard

• Very high MP

• Doesn’t conduct electricity

Describe the structure of graphite

• Each carbon atom forms 3 covalent bonds with 3 other carbon atoms

• Forms layers of hexagonal rings

• No covalent bonds between layers

Why is graphite conductive?

One electron from each carbon atom is delocalised

Why is graphite soft and slippery?

The layers can slide over each other

What is graphene?

A single layer of graphite

What does graphene’s properties make it useful in?

Electronics and composites

Why is graphene so strong?

The atoms in the layers are tightly bonded covalently

Why is graphene elastic?

The planes of atoms can flex relatively easily without the atoms breaking apart

What are fullerenes?

Molecules of carbon atoms with hollow shapes

What is the structure of fullerenes based on?

Hexagonal rings of carbon atoms

(may also contain rings with five or seven carbon atoms)

What was the first fullerene to be discovered?

Buckminsterfullerene (C₆₀)

What shape does buckminsterfullerene have?

Spherical

What are carbon nanotubes?

Cylindrical fullerenes with very high length to diameter ratios

What do the properties of carbon nanotubes make them useful for?

• Nanotechnology

• Electronics

• Materials

What can the fullerenes and carbon nanotubes be used for?

• Lubricants

• To deliver drugs in the body

• Catalysts

What can nanotubes specifically be used for?

Reinforcing materials (e.g. tennis rackets)

What does nanoscience refer to?

Structures that are 1-100 nm in size

How many atoms do nanoparticles contain?

A few hundred

Are nanoparticles or fine particles smaller?

Nanoparticles

What is the short form for fine particles?

PM_2.5

What diameters so fine particles have?

Between 100 and 2,500 nm