Bonding, structure and properties

Question 1

How is an ionic compound formed?

Answer 1

When a metal element reacts with a non-metal element.

Question 2

When is a covalent bond necessary?

Answer 2

When a non-metal element reacts with a non-metal element.

Question 3

What type of force is ionic bonds?

Answer 3

Electrostatic force of attraction.

Question 4

What sort of diagram can be expected showing an ionic bond?

Answer 4

A diagram of both elements, one with dots and the other with crosses. Brackets around each element, with 2- stating they have gained 2 electrons and 2+ stating they have lost 2 electrons.

Question 5

What is the overall aim with an ionic bond?

Answer 5

To either loose or gain electrons in the outer shell to get a full outer shell.

Question 6

In an ionic bond, does the metal or non-metal element transfer the electrons?

Answer 6

It is usually the metal element, meaning the metal element is usually stated as positive ions, whilst non-metals on the contrary.

Question 7

What are some examples of ionic bonds? (elements)

Answer 7

Sodium chloride, magnesium oxide, calcium chloride and lithium oxide among a few.

Question 8

What is a covalent bond?

Answer 8

A covalent bond forms when two non-metal atoms share a pair of electrons.

Question 9

Are covalent bonds strong or weak?

Answer 9

Covalent bonds are strong, and need a lot of energy to break them. Strong covalent bonds inside the molecules, very weak forces of attraction between molecules.

Question 10

Explain covalent bonding between hydrogen and chlorine.

Answer 10

Hydrogen has 1 electron in the outer shell, whilst chlorine has 7. When they merge together, an electron couplet is formed, meaning hydrogen now has 2 in the outer shell and chlorine has 8.

Question 11

Why do covalent bonds require a lot of energy to break?

Answer 11

Both nuclei are strongly attracted to the shared pair of electrons in the covalent bond, so covalent bonds are very strong and require a lot of energy to break.

Question 12

What is the maximum number of covalent bonds that can be formed?

Answer 12

4 bonds (eg 8 electrons in the centre of the diagram)

Question 13

How can you quickly work out the number of covalent bonds in an element?

Answer 13

Take the number in the outer shell (8) and take it away from the group number. Example, carbon is in group 4, has 8 electrons in the outer shell, 8-4=4, 4 bonds.
Hydrogen forms one covalent bond. The noble gases in Group 0 do not form any.

Question 14

What can be represented by a dot-and-cross diagram?

Answer 14

Covalent bonds. For example, CH4 (methane) has a carbon atom (4 electrons) and 4 hydrogen atoms (1 electron), so 4 covalent bonds are formed to stablise the atoms.

Question 15

What other way can double, triple and quadruple covalent bonds be represented as?

Answer 15

The letter, followed by horizontal lines connecting the next letter. For example, carbon dioxide (double bonds connecting carbon and oxygen) can be shown as
O–C–O, with the lines above each other though.

Question 16

What are the ions in a compound arranged as?

Answer 16

A giant ionic structure also known as a giant ionic lattice.

Question 17

Does it take a lot of energy to separate positive and negative ions in a crystal lattice?

Answer 17

Yes, due to its formation and the fact that there is no de-localised electrons. This is because of the strong electrostatic forces between them. This also means they have high melting and boiling points.

Question 18

Do solid ionic compounds conduct electricity?

Answer 18

Solid ionic compounds do not conduct electricity because the ions are held firmly in place. The ions cannot move to conduct the electric current. But when an ionic compound melts, the charged ions are free to move. Therefore, molten ionic compounds do conduct electricity.

Question 19

What happens when a crystal of an ionic compound dissolves in water?

Answer 19

When a crystal of an ionic compound dissolves in water, the ions separate. Again, the ions are free to move – so a solution of an ionic compound in water also conducts electricity.

Question 20

What is the main rule when drawing a lattice?

Answer 20

The lines connecting them should not be connecting identical ions.

Question 21

Explain the melting points of ionic compounds.

Answer 21

It takes a lot of energy to overcome the strong electrostatic forces of attraction between oppositely charged ions, so ionic compounds have high melting and boiling points. However, some have higher melting points than others. The greater the charge on the ions, the stronger the forces holding them together. Sodium chloride is made from Na+ ions and Cl– ions and has a melting point of 801°C. Magnesium oxide is made from ions with two charges (Mg2+ and O2–) and so has a much higher melting point of 2,852°C.

Question 22

What 2 types do covalently bonded substances fall into?

Answer 22

Simple covalent structures and giant covalent strucutres.

Question 23

What are the properties of a simple covalent structure?

Answer 23

Simple molecules contain only a few atoms held together by covalent bonds. An example is carbon dioxide (CO2), the molecules of which contain one atom of carbon bonded with two atoms of oxygen. The intermolecular forces between simple molecules are weak.

Question 24

What are the 2 key points of a simple covalent strucutre?

Answer 24

Low melting and boiling points, and they do not conduct electricity.

Question 25

What are the properties of a giant covalent structure?

Answer 25

Giant covalent structures contain very many atoms, each joined to adjacent atoms by covalent bonds. The atoms are usually arranged into giant regular lattices – extremely strong structures because of the many bonds involved. For example, diamond or graphite.

Question 26

What is an allotrope?

Answer 26

An allotrope is a different from of the same element in the same state. For example, diamond and graphite are allotropes of carbon.

Question 27

What are the 2 key points of a giant covalent structure?

Answer 27

Very high melting points and variable electrical conductivity.

Question 28

What is graphite?

Answer 28

Graphite is a form of carbon in which the carbon atoms form covalent bonds with three other carbon atoms. This means that each carbon atom has a ‘spare’ electron (as carbon has four outer electrons) which is delocalised between layers of carbon atoms. These layers can slide over each other. It is used in pencils. Graphite conducts electricity due to the ‘spare’ electrons being delocalised between the layers. This conductivity makes graphite useful as electrodes for electrolysis.

Question 29

What is electrolysis?

Answer 29

The decomposition of of a compound using an electric current.

Question 30

What is diamond?

Answer 30

Diamond is a form of carbon in which each carbon atom is joined to four other carbon atoms, forming a giant covalent structure. As a result, diamond is very hard and has a high melting point. This explains why it is used in cutting tools. It does not conduct electricity as there are no delocalised electrons in the structure.

Question 31

What is the physical structure of a diamond?

Answer 31

A diamond is one giant molecule of carbon atoms. Diamonds are colourless and transparent. They sparkle and reflect light, which is why they are described as lustrous.

Question 32

What is the physical structure of graphite?

Answer 32

Graphite contains layers of carbon atoms. Graphite is black, shiny and opaque. It is not transparent. It is also a very slippery material. It is used in pencil leads because layers easily slide onto the paper, leaving a black mark. It is a component of many lubricants, for example bicycle chain oil.

Question 33

What are nanotubes?

Answer 33

Nanotubes are a type of fullerene and are molecular-scale tubes of carbon arranged similarly to the layers in graphite. Carbon nanotubes have a very high melting point, as each carbon atom is joined to three other carbon atoms by strong covalent bonds. This also leaves each carbon atom with a spare electron, which forms a sea of delocalised electrons within the tube, meaning nanotubes can conduct electricity.

Question 34

Why are most metals malleable?

Answer 34

They consist of layers of ions that can slide over one another when the metal is bent, hammered or pressed. Due to the ions sliding over each other, most metals are ductile – they can be drawn/pulled into wires, making them suitable for electric cables.

Question 35

What is a metallic bond?

Answer 35

Metals form giant structures in which electrons in the outer shells of the metal atoms are free to move. The metallic bond is the force of attraction between these free-moving (delocalised) electrons and positive metal ions.

Question 36

What increases a melting/boiling point of a metal?

Answer 36

The greater the number of outer electrons that the metal has, the higher its melting/boiling point. This is due to the increased positive charge on the metal ion and the increased number of electrons that are delocalised, resulting in stronger bonding.

Question 37

What is the size of a nano particle?

Answer 37

A nano-scale particle is a particle of a substance that is 1 – 100 nm in diameter (1 nm = 1 nanometre = 1 × 10–9 m, which is one billionth of a metre).

Question 38

Why is nano-silver used?

Answer 38

• In wound dressings to prevent infection
• To coat the inside of socks and the inside of fridges to kill the bacteria that cause bad smells
• In deodorants to kill bacteria that cause bad smells
• To disinfect water supplies on the International Space Station

Question 39

What can titanium dioxide be used in?

Answer 39

Nano-scale particles of titanium dioxide can be used in sunscreen to block harmful ultraviolet light. This helps to prevent sunburn and skin cancer. These particles are so small that they cannot be seen and so make the sunscreen invisible.

Question 40

What are the issues regarding nano-particles?

Answer 40

It an area hardly researched and been around for a short amount of time. The particles are so small they can enter are blood stream, and some human cells. This opposes a health risk. They can also easily enter the environment and cause harm to animals by bioaccumulation.

Question 41

What are smart materials?

Answer 41

Smart materials are materials that have properties which change reversibly, ie can change easily but can then easily change back, depending on changes in their surroundings.

Question 42

What do thermochromic pigments do?

Answer 42

Thermochromic pigments change colour at specific temperatures. Examples include colour-changing novelty mugs, colour-changing spoons, battery power indicators and forehead thermometers.

Question 43

What do photochromic pigments do?

Answer 43

Photochromic pigments change colour when exposed to light. This can be used in clothing but is most commonly found in photochromic lenses for glasses, which darken when exposed to ultraviolet light.

Question 44

What is a shape memory polymer?

Answer 44

Shape memory polymer is a polymer that can be bent out of its original shape and then returned to its original shape when heated. Potential applications for this include sporting equipment, such as helmets and gum-shields or car bumpers, which can be heated to return to their original shape after a minor collision. In addition, medical stitches can self-tighten as a wound heals.

Question 45

What is a shape memory alloy?

Answer 45

Shape memory alloys are mixtures of metals that return to their original shape when heated, similar to shape memory polymers. Again, this type of smart material could be used in sporting equipment and car bodies, as well as certain medical applications, such as surgical plates for joining bone fractures. As the alloy is warmed by the body, it applies a greater tension than normal plates, allowing for faster healing.

Question 46

What are hydrogels?

Answer 46

Hydrogels can absorb up to 1,000 times their own volume in water. After this water has been absorbed, it can be released when its surroundings are dry. Changes in temperature or pH can also cause the hydrogel to release water.

Question 47

What are the applications of hydrogels?

Answer 47

• Artificial muscles
• Hair gel
• Nappies
• ‘Magic’ expanding snow
• Granules added to soil to help retain water for plants