Topic 2a- Bonding, structure and the properties of matter

What are ions?

Ions are charged particles

What can ions be?

They can be single atoms, or groups of atoms

When are ions made?

When an atom loses or gains an electron

How to Metal atoms form ions?

They lose electrons to form positive ions (Cations)

How do non-metal atoms form ions?

They gain electrons to form negative ions -(Anions)

What are atoms trying to do by losing or gaining electrons to form ions?

To get a full outer shell like a noble gas (also called a “A stable electronic structure”) - Atoms with full outer shells are very stable

What do elements in the same group have the same number of?

The same number of outer electrons - so they have to lose or gain the same number of electrons to get a full outer shell - this means they will all form ions with the same charges

What do negative ions have the end of their element name replaced with?

With -ide, for example oxide, sulfide, fluorine, bromine

What is ionic bonding?

When metals react with non-metals, and electrons are transferred from the metal atoms to the non-metal ions

• The metals atoms lose electrons to become positively charged ions with a full outer shell

• he Non- metal atoms gain electros to become negatively charged ions with a full outer shell

What happens in ionic bonding?

The oppositely charged ions are strongly attracted to each other, and this string electrostatic force holds the ions together in an ionic compound

What are Dot and Cross diagrams used for?

To show what happens during ionic bonding - The electrons in one type of atom are represented by dots, and the electrons in the other type of atom are represented by crosses - This means you can tell which atoms the electrons in an ion originally came from

What structure does an ionic compound have?

A structure called a giant ionic lattice , held together by very strong electrostatic forces of attraction between oppositely charged ions which act in all directions

Which diagrams and models are ionic compounds represented by?

• Dot and cross diagrams

• 3D models

• Ball and stick models

What do 3D models show?

3D models shows the relative sizes of the ions, as well as the regular pattern in an ionic crystal

What is a disadvantage of a 3D model?

They only let you see the outer layer of the compound

What do Ball and Stick models show?

The regular pattern in an ionic lattice, as well as how all the ions are arranged - In addition, they suggest that the crystal extends beyond what is shown in the diagram

What are the disadvantages of a Ball and Stick model?

• They may not show the relative sizes of ions, but sometimes the ions are not shown to scale

• They suggest that there are gaps between the ions, when in reality there aren’t

What is the empirical formula?

The simplest whole number ratio of atoms in a compound

How would you find the empirical formula from a dot and cross diagram?

Count up how many atoms there are of each element

How would you figure out the empirical formula from a 3D model or a ball and stick model?

You need to use the diagram to work out what ions are in the ionic compound - You then have to balance the charges of the ions so that the overall charge on the compound is zero

What are the melting and boiling points of Ionic compounds like?

Ionic compounds all have high melting points and high boiling points due to the strong electrostatic attraction between the ions - it takes a large amount of energy to overcome this attraction and break the many strong bonds

What is the solubility of Ionic compounds like?

Most ionic compounds dissolve easily in water - because parts of water molecules are slightly charged and so can pull the ions away from the lattice

What is the electrical conductivity like in ionic compounds?

Ionic compounds don’t conduct electricity when solid because the ions are all held in fixed positions - However, when they’re melted or dissolved, the ions are free to move and they’ll carry electric current

What is an electric current?

A flow of charged particles, which can either be ions or free electrons

What is covalent bond?

A covalent bond is formed when a pair of electrons is shared between two atoms - atoms share electrons with each other to get full outer shells

What happens to the atomsd in covalent bonding?

They only share electrons in their outer shells and both atoms involved in the bond end up with one extra electron in their outer shell

What makes covalent bonds very strong?

The positively charged nuclei of the bonded atoms are attracted to the shared pair of electrons by electrostatic forces, making covalent bonds very strong

What does each single covalent bond provide?

One extra shared electron for each atom

What does each atom involved have to make?

Enough covalent bonds to fill up its outer shell so they have the electronic structure of a noble gas (which is very stable)

Between which type of atoms does covalent bonding occur?

Between non-metal atoms - this can either be in non-metallic elements, or in compounds of non-metals

How are covalent bonds represented in a dot and cross diagram?

The shared electrons can be drawn in the overlap between the outer orbitals of the two atoms - just the outer electron shells are shown in these diagrams

How do dot and cross diagrams represent double covalent bonds?

E.g - the double covalent bond formed by the oxygen atoms in oxygen gas - To get full outer shells, each oxygen atom has to share two electrons with another oxygen atom, meaning two pairs of electrons are shared between each pair of oxygen atoms

What are dot and cross diagrams useful for?

Showing which atoms the electrons in a covalent bond come from

What is a disadvantage of dot and cross diagrams?

They don’t show the relative sizes of the atoms, or how the atoms are arranged in space

What does a displayed formula show?

A displayed formula shows the covalent bonds as single lines between atoms - it is a great way of showing how atoms are connected in large molecules

What is a disadvantage of Displayed formulas?

They don’t show the 3D structure of the molecule, or which atoms the electrons in the covalent bond have come from

What does a 3D model show?

A 3D models shows the atoms and their arrangement in space next to each other

What are the disadvantages of 3D models?

• Ball and stick models show the bonds, (and double bonds) whereas 3D models don’t

• They can quickly get confusing for large molecules where there are lots of atoms to include - They don’t show where the electrons in the bonds have come from either

How can you find the molecular formula of a simple molecular compound?

By counting up how many atoms of each element there are in a diagram of the molecule

What are the two types of covalent bonds?

Simple molecules and macromolecules

What are simple molecules made up of?

Simple molecules made up of only a few atoms joined by covalent bonds

What are examples of simple molecules?

Hydrogen, chlorine, hydrogen chloride, methane, ammonia, nitrogen and oxygen

Describe a hydrogen atom and its bonds :

• Hydrogen atoms have just one electrons

• They only need one more electron to complete the first shell, so they often form single covalent bonds to achieve

Describe a chlorine atom and its bonds 😃

• Chlorine atoms need one electron to gain a stable electron structure

• Two chlorine atoms each share one of their electrons to form a chlorine molecule containing one shared pair of electrons - a single covalent bond

Describe hydrogen chloride and its bonds (CH4) :

• The bonding in hydrogen chloride is very similar to the bonding in hydrogen and chloride

• Both atoms only need one more electron to complete their outer shell, so they share one pair of electrons and one single covalent bond is formed

Describe Methane and its bonds 😃 (CH4)

• Carbon has 4 outer electrons, which is half a full shell

• So, it forms four covalent bonds to make up its outer shell

• Hydrogen atoms only need to form one covalent bond to achieve a full outer shell

• So, a carbon atom will form covalent bonds with four hydrogen atoms to form a CH4 molecule

Describe water and its bonds (H20) :

• Oxygen atoms have six outer electrons

• They sometimes form ionic bonds by taking two electrons from other atoms to complete their outer shell

• However, they’ll also form covalent bonds and share two electrons instead

• In water molecules, the oxygen shared electrons with two hydrogen atoms to form two single covalent bonds

Describe Nitrogen and its bonds (N2) :

• A nitrogen atom has five electrons in its outer shell, so it needs three more to fill it

• Two nitrogen atoms can each fill their shells by sharing three pairs of electrons - this creates a triple bond which is very strong, and why nitrogen is unreactive

What is the electrical conductivity of simple molecules What is th?

Covalent substances made up of simple molecules don’t conduct electricity in any state - there are no ions or free electrons so there’s nothing to carry an electrical charge

What are the melting and boiling points like in simple molecules?

• Covalent substances, made up of simple molecules, how low melting and boiling points, so the are mostly gases or liquids at room temperature, but they can be solids

• They have a low boiling point because although he atoms within the small molecules form very strong covalent bonds with each other, the forces of attraction between the molecules (intermolecular forces) are very weak

What are intermolecular forces?

Forces between separate substances that hold the substance together - its the intermolecular forces that must be overcome in order to melt or boil a simple molecular substance - not the much stronger covalent bonds

Overcoming these weak intermolecular forces does not take much energy , so the melting and boiling points are low

What are substances with larger molecules likely to be?

Solids at room temperature

What happens as molecules get bigger?

As molecules get bigger, the strength of the intermolecular forces increase, as more energy is needed to break them, and the melting and boiling points increase

How do the number of electron shells of an element relate to the melting and boiling points of an element?

The more electron shells, the larger the atom and the greater the strength of the intermolecular forces

What is iodine at room temperature?

Iodine is a solid at room temperature, whilst all he halogens above it in the group are liquids or gases

What is a polymer?

A polymer consists of lots of long molecules made up of repeating sections

How are the atoms in a polymer joined?

All the atoms in a polymer are joined by strong covalent bonds

How are polymer molecules formed?

Polymer molecules are formed when lots of small units link together

What can many ethene molecules be joined up to produce?

Many ethene molecules can join up to produce poly(ethene) or “polythene”

How many atoms can a polymer atom contain?

Thousands or even millions of atoms , so it would be pretty difficult to draw it in full - instead you can draw the shortest repeating section, called the repeating unit put it in large brackets and put the n after the brackets to show it is repeated many times

How would you write down the molecular formula of a polymer ?

Write down the molecular formula of the repeating unit by counting the number of atoms of each element it contains, put brackets around it and out and ‘n’ after the brackets

What are the melting and boiling points of polymers?

• Polymers have higher melting points and boiling points than simple covalent molecules

• This because the intermolecular forces between the larger polymer molecules are stronger, so more energy is needed to break them

• This means that polymers are solid at room temperature

Why do polymers generally have lower boiling points than ionic or covalent compounds?

Because the intermolecular forces in polymers are still weaker than ionic or covalent bonds

What needs to be overcome to melt a polymer?

Only the intermolecular forces, the covalent bonds inside the molecules don’t need to be broken

What are giant covalent structures (macromolecules) ?

They are similar to giant ionic structures (lattices) but there are no charged ions

How are the atoms bonded n Giant covalent structures?

All the atoms are bonded to each other by strong covalent bonds

What are common examples of giant covalent structures?

Diamond and graphite, which are both makes only from carbon atoms, and silicon dioxide (silica)

How would you melt or boil a giant covalent molecule?

You need to overcome the strong covalent bonds between the atoms - this takes a lot of energy, so giant molecules have very high melting and boiling points

What are diamond and graphite?

Allotropes of carbon - different structures of the same element

What are allotropes ?

Different structural forms of the same element in the same physical state - e.g- they’re all solids

What are the four allotropes of Carbon?

Diamond, graphite, graphene, fullerenes

Describe the structure of Diamond?

• each carbon atoms forms four covalent bonds with other carbon atoms - This forms a very rigid structure, which is why Diamond is so hard

Why does Diamond have a very high melting point?

Because the strong covalent bonds take a lot of energy to overcome

Why does Diamond not conduct electricity?

Because it has no free electrons or ions

What is the structure of graphite?

In graphite, each carbon atom only forms three covalent bonds - this creates sheets of carbon atoms arranged in hexagons

What are the layers of carbon atoms in Graphite held together by?

By weak intermolecular forces, so the layers are free to move over each other - this makes graphite soft and slippery, so it’s ideal as a lubricating material

What makes graphite soft and slippery?

There aren’t any covalent bonds between layers- they’re only held together by weak intermolecular forces, so they’re free to move over each other

Why does graphite have a high melting point?

Because the covalent bonds in the layers need a lot of energy to break

Why can graphite conduct electricity and thermal energy?

Only three out of each of carbon’s four outer electrons are used in bonds, so each carbon atom has one electron that’s delocalised (free) and can move

What does a substance need in order to conduct electricity?

charged particles (ions or electrons) which are free to move

What is the structure of Graphene?

Graphene is a sheet of carbon atoms joined together in hexagons - It’s basically a single layer of graphite - the sheet is just one atom thick, making it a two-dimensional compound

What makes graphene very strong?

The network of covalent bonds

What are the physical properties of Graphene?

• Very strong - network of covalent bonds

• Incredibly light - so they can be added to composite materials to improve their strength without adding much weight

How can graphene conduct electricity?

It contains delocalised electrons, so can conduct electricity through the whole structure - this means it has the potential to be used in electronics

What are fullerenes?

Hollow molecules of carbon, shaped like tubes or balls

What are fullerenes made up of?

They are mainly made up of carbon atoms arranged in hexagons, but can also contain pentagons (rings of 5 carbon atoms) or heptagons (rings of 7 carbon atoms)

What was the Buckminsterfullerene?

The first fullerene to be discovered - It’s got the molecular formula C60 and forms a hollow sphere containing 20 hexagons and 12 pentagons

What are nanotubes?

Nanotubes are fullerenes which are tiny carbon cylinders - the ratio between the length and the diameter of nanotubes is very high - They’re good conductors of heat and electricity

How can fullerenes be used in medicine?

• Fullerenes can be used to ‘cage’ other molecules

• The fullerene structure forms around another atom or molecules, which is then trapped inside

• This could be used to deliver a drug to where it is needed in the body in a highly controlled way

How can fullerenes be used as catalysts?

• Fullerenes have a huge surface area, so they could help make great industrial catalysts - individual catalyst molecules could be attached to the fullerenes (the bigger the surface area the better)

How can fullerenes be used as lubricants?

• coating moving machine parts in fullerenes dramatically reduces friction

• They could be used to reduce friction in artificial joints

How can fullerenes used to strengthen materials?

• Nanotubes have a high tensile strength (they don’t break when stretched) so they can be used to strengthen materials without adding much weight, such as in tennis racket frames

How can fullerenes be used in electronics?

• Nanotubes can conduct electricity, and they’re very small, so they can be used in very small electrical circuits, for example in the microchips found in computer and phones

What is technology that uses small particles such as nanotubes called?

Nanotechnology

What is the structure of metals?

Metals consist of a giant structure

How are the atoms in a metal arranged?

In a regular pattern

Why are metals said to have giant structures?

Because they have lots of atoms - exactly how many depends on how big the piece of metal is

What does it mean that the electrons in the outer shells of the atoms are delocalised?

They aren’t associated with a particular atom or bond - they’re free to move through the whole structure

What type of bonding holds metals together?

Metallic bonding - There are strong forces of electrostatic attraction between the positive metal ions and the negative electrons and these forces

What are the melting and boiling points like in metals?

• The electrostatic forces between the metal atoms and the delocalised sea of electrons are very strong , so need lots of energy to be broken

• This means that most compounds with metallic bonds have very high melting and boiling points, so they’re generally solid at room temperature