Atomic Structure Peq's

Question 1

What is the trend in the first ionisation energy of group 2 elements

Answer 1

Decreases as the ions get bigger therefore there is a weaker attraction of ions to lost electrons

Question 2

Why is it necessary to ionise molecules when measuring their mass in a Tof mass spec

Answer 2

So the ions will interact with and be acceelerated by a electric field only ions will create current and be detected

Question 3

Which of the elements magnesium or aluminium has the lower ionisation energy

Answer 3

Aluminium as the outer electron is in a p orbital and can be removed easily

Question 4

What requires more energy for the outer electron to be removed an ion or an atom

Answer 4

An ion as it is already stable more preferably with less energy so a smaller ion. A electron can be removed more easily if it is in a higher orbital

Question 5

State the element in period 3 with the highest melting point

Answer 5

Silicon as it contains many covalent bonds which may require lots of energy to be removed

Question 6

State the element in period 3 with the highest electronegativity or highest first ionisation energy

Answer 6

Argon as it has the highest nuclear charge- most numbers of protons compared to others and the same number of electron shells and shielding etc

Question 7

What is electronegativity

Answer 7

The ability of an atom to attract a pair of electrons towards itself within a covalent bond

Question 8

Suggest the element in period 3 with the highest electronegativity value

Answer 8

Chlorine

Question 9

What is not deflected by a electric field protons or neutrons or electrons

Answer 9

Neutrons

Question 10

Explain why the second ionisation energy for boron is higher then the first energy

Answer 10

Because the electron is removed from a positive ion so it needs more energy to be removed, and it is closer to the nucleus.

Question 11

Explain it terms of its structure and bonding why nickel has a strong mp

Answer 11

It contains positive metal ions and delocalised electrons, there is a strong attraction between them (metallic bond) hence more energy is required to overcome them.

Question 12

Explain why nickel is ductile

Answer 12

As it has layers of atoms which can slide over each other.

Question 13

Why is the second ionisation energy of silicon lower than the second ionisation energy of aluminium

Answer 13

As the electron in silicon is removed from a 3p orbital and there is more shielding so it is lost easier

Question 14

Predict the element in period 3 that has the highest 2nd ionisation energy and why

Answer 14

Sodium as the electrons removed are nearer to the nucleus so it is harder to remove

Question 15

Why is the ionisation energy of every element endothermic?

Answer 15

As heat energy is required to overcome the attraction between the negative electrons and the positive nucleus

Question 16

State what can be adjusted in the mass spec to enable ions formed by the different isotopes to be directed onto the detector

Answer 16

The electric field or electromagnet

Question 17

Name one instrument which is used to measure the relative abundance of isotopes

Answer 17

Mass spectometer

Question 18

If it wants the 95 percent yield of something in an equation but gives you hypothetically 100 percent how do you work out the mass of it

Answer 18

You basically get the element we’re provided information for and use it and work out its moles. That moles is for 100 percent of it so we work out 95 percent so do that /95 times 100 to get 95 percent. And whatever moles you get is what you need to work with for the rest of the equation doing what you need to it for example using the molar ratio working out its mass whatever.

Question 19

Write an ionic equation with state symbols to show the reaction of calcium with excess water

Answer 19

Ca(s)+2h20(l)—>ca2+(aq)+20H-(aq)+h2(g)

Question 20

Give the electronic config of cr3+

Answer 20

Chromium= 4s1 3d5
Cr+=4d0 3d5
Cr2+=3d4
So cr3+ is (Ar)3d3

Question 21

State the two measurements that are recorded for each isotope

Answer 21

• relative abundance

- m/z

Question 22

Explain how the relative abundance of an ion is measured in a mass spec

Answer 22

The ions hit the detector picking up an electron allowing a current to be generated as a movement of charge occurs. The bigger the current the higher the abundance of ions.

Question 23

A sample of rubidium contains the isotopes 85rb and 87rb only. The isotope 85 rib has an abundance 2.5 times greater than that of 87rb.
Calculate the ram of rubidium in this sample

Answer 23

You do
(85 times 2.5) + (87 times 1)
———————————————-
3.5

3.5 as you add 2.5 and 1

Question 24

State and explain how al and s deviate from the general trend

Answer 24

Al as an electron is removed from 3p which is a higher sub shell so can be lost easier

S- as the electron is removed from a 3p electron pair so repulsion between e- means lost easier

Question 25

Name 3 processes that occur in a mass spectrometer before detection and explain how

Answer 25

Ionisation- high energy electrons fired at the sample knocking off an outer electron

Acceleration- electric field

Deflection- due to the magnetic field

Question 26

25mg atoms make up 10 percent by mass in a sample of magnesium magnesium has an ar of 24.3 use this to deduce the percentages of the other two magnesium isotopes present in this sample (mg26 and mg24)

Answer 26

So, 24.3=(25 times 10)+(24 times x) +(26times 90-x) bc the other two obviously are 90 so x and 90-x. Then re arrange it so 2430=250 times 24x times 2340-26x/100 then times by 100 - number divide by 2 and you should get x as 80 which means 90-80 is 10 so the other one is 10

Question 27

If it gives you two mass numbers of isotopes and 2 relative abundance’s use this info to work out the relative abundance and the mass of the third isotope if total ram is 32.16

Answer 27

You do the first mass and abundance times the second one and for the third one (write the mass as x and the relative abundance do the previous two-100) so you get x and whatever number over 100. Then re arrange and solve for x. There you go thats your mass number

Question 28

Define ionisation energy

Answer 28

Energy required to remove 1 outer electron from each atom in 1 mole of gaseous atoms to form one mole of gaseous ions

Question 29

What do you have to add with ionisation energy equations

Answer 29

The gas state symbol bc remember their gases. Eg Mg+(g)—>Mg2+ +e-

Question 30

Why does it take more energy for the second ionisation energy of mg

Answer 30

As the electron is being removed from a positive ion so the electron is being removed closer to the nucleus

Question 31

Explain how the ions are held together in solid sodium metal

Answer 31

Strong electrostatic forces of attraction between the positive ions and the negative delocalised electrons.

Question 32

Explain how ions are held together in solid sodium chloride

Answer 32

Electrostatic forces of attraction between oppositely charged ions

Question 33

Why does sulfur deviate from the general trend of first ionisation energies

Answer 33

As there are two electrons in a 3P orbital which repel each other.

Question 34

Which element deviates from a general trend from the period 2 elements

Answer 34

Boron/oxygen

Question 35

Suggest why the iron (III) oxide obtained is pure, assume a complete reaction

Answer 35

As all other products are gases(will escape and not contaminate iron iii oxide)

Question 36

Why is the na+ ion smaller than the f- ion

Answer 36

As it contains more protons so has a stronger attraction for its outer electrons and so is smaller in size

And both na+and f- have the same electron arrangement so similar shielding

Question 37

Why would smth have a large atomic radius

Answer 37

If it has less protons as then there is less attraction between protons and electrons.

Question 38

When would something have a smaller atomic radius

Answer 38

When it has a higher nuclear charge, bc more attraction between protons and electrons

Question 39

Deduce the element in period 2 that has the highest second ionisation energy

Answer 39

Lithium - small when ion hard to remove the electron greater attraction between ion and lost electrons

Question 40

describe how ions are formed in a tof mass spectrometer

Answer 40

Apply high voltage, atoms lose electrons

Question 41

explain electrospray

Answer 41

sample dissolved in a volatile solution, injected through needle at high pressure EACH MOLECULE gains a proton

Question 42

the first ionisation energies of the elements in period 2 change as the atomic number increases. explain the pattern in the first ionisation energies of the elements from lithium to neon (6 marks)

Answer 42

first ionisation energies increase along the row, nuclear charge increases and greater attraction between nucleus and outer electrons making it harder to remove the electrons and shielding is similar

deviation between be and b. b’s first ie is lower than be as it is in the 2p subshell which is higher in energy meaning that electron can be removed

deviation between n and o easier to remove electrons in o because 2p subshell contains electron pair which causes repulsion meaning the electron is easier to remove

Question 43

state two measurements recorded for each isotope

Answer 43

m/z and abundance

Question 44

explain why the ionisation energy for every element is endothermic

Answer 44

as heat energy is required to overcome the attraction between the positive nucleus and the negative electrons

Question 45

explain why chromium is placed in the d block in the periodic table

Answer 45

as its outer electron or highest energy electron is in the 3d subshell, or has an incomplete d subshell