Chapter 3 - Atoms & Bonds

Question 1

What does an atom exist of?

Answer 1

A nucleus consisting of protons and neutrons, surrounded by electrons.

Question 2

What is the chemical formula of Argon gas?

Answer 2

Ar

Question 3

What does the subatomic scale describe? Why is it important?

Answer 3

The behaviour and structure of elementary particles of atoms. It can be used to describe magnetic and electric behaviour.

Question 4

What does the atomic scale describe? Why is it important?

Answer 4

The bonding of different atoms and their arrangement. This can be used to describe elastic behaviour for example.

Question 5

What does the microscopic scale describe? Why is it important?

Answer 5

Depending on the type of microscope (Electron or light) It can be used for heat treatments

Question 6

What does the macroscopic scale describe? Why is it important?

Answer 6

Different parts and structures of the end product like reinforced concrete. This is important for different properties: making a sandwich-panel with a honeycomb core to have a light yet relatively strong material.

Question 7

Give and describe the 4 quantum numbers.

Answer 7

principal quantum number [n] (hoofdkwantumgetal) – shows the energy level: orbitals (number);
secondary quantum number l – l is connected to a letter (l =0: s, l =1: p, … d, … f etc.);
magnetic quantum number [m_l] – goes from -l to +l (all of these) rotation around nucleus creates a field;
spin quantum number [s] – shows which direction the electron spins in: given by -1/2 or +1/2;

Question 8

Give the Pauli exclusion principle.

Answer 8

No 2 electrons can have the same quantum state, meaning that always at least 1 quantum number will be different from the other.

Question 9

Is the density of atoms enough to find the density of the material?

Answer 9

No, carbon for example has a graphite form and a diamond form. They have different densities even though carbon’s density itself is constant.

Question 10

What are the consecutive building blocks that an object consists of?

Answer 10

Atoms/ions -> molecules -> macromolecules

Question 11

A stiff material:

Answer 11

Can withstand big stresses without deforming a lot. This has a steep incline on the graph. This is caused by strong bonds

Question 12

A strong material:

Answer 12

Can withstand a lot of stress before a form of failure occurs (like plastic deformation or breaking). This is not just caused by the bond strength but also other factors [which –> later in this chapter].

Question 13

What is electronegativity?

Answer 13

The tendency to attract an electron.

Question 14

Why is Argon a commonly used gas for welding?

Answer 14

It doesn’t react with anything and can be used for welding since it will not react with molten metal.

Question 15

Why do atoms want to reach the noble gas configuration (8 valence electrons)

Answer 15

Because it’s the most stable.

Question 16

Why is F so the most electronegative?

Answer 16

It only needs 1 electron to reach the noble gas configuration and it doesn’t have a lot of orbitals (so the orbital to which the electron will be added is closer to the positive nucleus and thus there is more attraction)

Question 17

Why does H have an electronegativity of 2.1

Answer 17

If hydrogen loses another electron it would just be a nucleus with no electrons around it, the octet structure doesn’t count for hydrogen since the first shell only needs 2 electrons to be complete (Like Helium. H has more tendency to attract an electron.

Question 18

What are the different types of bonds?

Answer 18

Ion-, covalent, metallic and secondary bonds

Question 19

What is an ionic bond?

Answer 19

An electropositive atom gives an electron to an electronegative atom, which gives them an opposite charge and makes them attract each other. This is a strong bond

Question 20

When does an ionic bond occur?

Answer 20

When there is a big difference in electronegativity (typically > 1.7). This means that it is a bond between a non-metal and a metal.

Question 21

True or false: cations are positively charged and anions are negatively charged?

Answer 21

True

Question 22

What makes an ionic bond so dense?

Answer 22

non-directional attraction makes them form a lattice. The distance between 2 equal charges is greater than the distance between 2 opposite charges and thus will the attraction forces dominate.

Question 23

What type of bond is present when there is a small difference in electronegativity? (and non-metallic)

Answer 23

Covalent bond

Question 24

What is a covalent bond? is it directional?

Answer 24

When electrons are shared in shared orbitals. It is directional

Question 25

What is the difference between graphite and diamond?

Answer 25

Diamond has 4 covalent bonds, graphite has only 3. This makes Diamond stiff in all directions and that makes it such a hard material. Graphite is stiff in only one direction. This means that different layers can slide over each other since they are only held together by secondary bonds which makes it a good lubricant

Question 26

Which types of bond are often found in polymers?

Answer 26

Covalent and secondary bonds.

Question 27

What is a metallic bond?

Answer 27

Bond where electrons are shared with neighbours, forming a sea of electrons with positive metal ions in it. The attraction between these charge carrying entities keeps them together.

Question 28

What are secondary bonds?

Answer 28

Bonds as a result of permanent or temporary dipoles. Also called Van der Waals forces.

Question 29

What are temporary (induced) dipoles?

Answer 29

When 2 molecules come near each other, the fluctuations of their charge distributions causes a weak temporary bond. (this means that at a certain time t, one side of the molecule might be slightly negatively charged due to more electrons being on that side) This happens for more atoms at once and the slightly negative side might attract a slightly positive side of another atom. (The same can be applied for molecules as for noble gas atoms)

Question 30

What can we say about the boiling point of molecules that form temporary dipoles?

Answer 30

Low boiling points, increasing boiling point as noble gas atoms/molecules get bigger

Question 31

When does a permanent dipole occur? Give an example

Answer 31

When a polar molecule is present, this means that when there is a small difference in electronegativity so 2 non-metal bonds, that there will be partial charges, this creates a dipole moment.
HF for example F has more tendency to attract electrons and this will have a higher concentration of electrons around itself. creating a partial negative charge, the opposite counts for the H atom.

Question 32

How can polar molecules induce a temporary dipole?

Answer 32

The difference in charge creates a small field that disturbs the distribution in non-polar molecules, causing a temporary dipole. This can be confirmed by Coulomb’s charge laws.

Question 33

What is the strongest secondary bond?

Answer 33

hydrogen bonds

Question 34

What are hydrogen bonds?

Answer 34

When H bonds covalently to one of the 3 most electronegative atoms (N, O, F) it can form hydrogen bonds This gives the H a positive partial charge. This charge can attract the negative partial charge the electronegative part of another molecule.

Question 35

Metals have ___ bonds

Answer 35

metallic

Question 36

Ceramics and glass have ___ bonds

Answer 36

Mixed Ionic/covalent

Question 37

polymers have ___ intramolecular and ___ intermolecular bonds

Answer 37

Covalent; secondary

Question 38

Why don’t ions go closer together than they are?

Answer 38

When 2 ions of opposite charge come closer and closer, first the attraction forces will dominate. When they are brought even closer, the repulsion force of both electron clouds of each ion and both nuclei becomes greater and greater until it is equal to the attraction force and they are in equilibrium. Note: this is only at 0 K, since thermal vibration needs to be taken in consideration!

Question 39

When we pull a rod, why does it get thinner?

Answer 39

Like a stack of bottles, when the bottom row is pulled apart a bit, then the rest of the bottles on top will roll down a bit. This is the same for balls that represent atoms.

Question 40

Why is argon used in welding?

Answer 40

The higher the temperature of a metal, the more it has a tendency to react with gasses or dust in the air. The argon is there because it is an inert gas, it will replace the air where the weld is done and this gives a higher quality weld since oxides are often less strong or have negative influences on one or more properties.

Question 41

Why are Van der Waals bonds much weaker than primary bonds (covalent, ionic, metallic)?

Answer 41

There is no transfer or sharing of electrons

Question 42

why is Li such an interesting material for batteries?

Answer 42

Light material, small molecules and a lot of tendency to give of an electron

Question 43

What is such an interesting property of tungsten (W)

Answer 43

Metal with the highest melting point. It is used in welding and in old lamp bulbs

Question 44

What type of bond do we find in diamond?

Answer 44

Covalent

Question 45

What type of bond do we find in rubber?

Answer 45

Covalent in chains; Secondary bonds between chains

Question 46

Which will have the highest E-modulus: PE or Nylon?

Answer 46

Nylon: it can form hydrogen bonds with the dipole character of NH and CO. PE can only form induced dipoles

Question 47

Which type of bonding usually leads to a lower density material?

Answer 47

Covalent: Because they are the only type of bond that have directionality.

Question 48

Why is it easier to recycle PET than to recycle rubber?

Answer 48

PET has secondary bonds in between chains. Rubber has crosslinked parts (which are covalent bonds). And to melt the molecules need to be able to slide over each other, which is not possible before these covalent bonds are broken. The S in rubber chains gets crosslinked.

Question 49

What is vulcanised rubber?

Answer 49

First, when there is no crosslinking, the material can be brought to a high temperature to get moulded into the right form. Then the material is brought to a specific temperature to create the crosslinks. This is nice in the automotive industry: we don’t want tires to melt when they get hot.

Question 50

What are thermoplastics?

Answer 50

Plastics that can be molten and remolten. This is nice for injection moulding.

Question 51

What are thermosets? (thermoharders in NL)

Answer 51

Plastics that once they are set, cannot be molten anymore due to crosslinks. They can still be injection moulded, but only before they are set, so the 2 chemicals are injected into the mould. Once they are set the polymer is made and it will not melt anymore. The disadvantage is that this process takes longer and it’s harder to recycle these polymers

Question 52

Why does graphite have a lower density than diamond?

Answer 52

Graphite has only 3 covalent bonds and 1 secondary bond, which is a weaker bond and thus is pulled less far in that direction, meaning a lower density.

Question 53

Is there a specific difference in density between metallic and ionic bonds?

Answer 53

No, there are different types of crystal structures that all have different densities. And for metallic bonds, it’s also dependent on the specific atom that it consists of.