Tutorial Chapter 2_asnw

7/29/2019 Tutorial Chapter 2_asnw

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Tutorial Chapter 2

1. Which of the following element has three two unpaired electrons in each of its

particle?A. Na

+B. Cl

-C. B D. Si

*Adapted from 2010 May/ June Paper 1

Answers: D (bonus for everyone)!

2. An X2+

ion has 20 protons. What is the electronic configuration of X2+

?

Answers: 1s2 2s2 2p63s23p6

3.

4.

5.

Answers: 3. B4. A5. A

6.

Answers: A



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7. The first seven ionisation energies of an element of a Period 3 are as follows.

a. What is the electronic configuration of the element? 1s22s22p63s23p4

b.

What is the element? sulfur *Adapted from 2009 May/ June Paper 1

8. Plot a graph the represents the number of unpaired p orbital electrons for atoms with

proton number 13 to 18.* 2009 May/ June Paper 1

Answers:No. of unpaired p orbital e-

Proton number

9. Identify the composition of the ions below.

Use of the data booklet is relevant for this question.

Protons Neutrons electrons

Mg+

12 12 10

O-

8 8 10

Cr 24 28 21I- 53 74 54

*Adapted from 2008 May/ June Paper 1

10. The particles in each of the following pairs differ only in the number of protons or

neutrons or electrons. Explain what the difference is within each pair

a. 6Li and

7Li

Answers: different neutron b.

32S and

32S

2-

Answers: different electron

c.39

K +

and Ca2+

Answers: different proton

11. Define an isotope. Quote an example that you know of and state their difference in a

table form. Answers: Atoms of the same element with the same proton number but differentnucleon number (or number of neutron). For example, carbon exists in 3 differentisotopes, with the same proton number of 12 but nucleon number of 12, 13 and 14.

1000 2252 3357 4556 7004 8496 27,107 31,719 36,621 43,177 kJmol-1



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12. The diagram below shows the energy level of the orbital present in atoms of the

third period.

a. Label the energy levels to indicate the principal quantum number and the typeof orbital at each energy level.

3p3s

2p2s

1s

b.

On the axes below, draw a sketch diagram of one of each different type of orbitalthat is occupied by the electrons in the third-period element. Label each type.

c. Using the energy level diagram above, show the electronic configuration for the

elements/ ion below.

i. Ne 1s22s22p6

ii. K + 1s22s22p63s23p6

iii. Mn2+ 1s22s22p63s23p63d5

iv. N3- 1s22s22p6

Answers are to be represented with energy level diagram as requested

d. In your own sentence, explain the following observations (you may want to cite

some elements as examples to facilitate your explanation)i. The first ionization energy of the elements decrease down a group

Model answers: Jia Wei’s: When going down a group, the atomic size increases. Therefore, the distanceof outer electrons from the nucleus increasesand the force of attraction

between the nucleus and the electron decrease. Hence, it is easier to removethe electronsand the ionization energy required is lower.

energy

x

z

y

x

z

y



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Naveen’s:

The elements have same valence electrons which is 2. But, t he valenceelectron shellsare different which is in increasing order. So, the distancebetween nucleus and the outer electron increases. The shielding by innershells increases. These factors outweigh the increased nuclear charge. This

causes the force of attraction to decrease. As a result, the first ionizationenergy of the elements decreases down a group.

Xian Qing’s: The first ionization energy of the element decreases when go down a group.This is because the distance of outer electrons from the nucleus increases asthe increasing number of electron shell. With the increase of atomic radius,the attraction force between the nucleus and the valence electron becomesweaker. Thus, it is easier to remove the electron and ionization energy isreduced. Another reason is the shielding effect of inner electrons increase when going

down the group. The valence electron experiences lesser attraction forceand causes the ionization energy to be lower.

Recommended answers: As the shell number increases down the group, its atomic size increases aswell. This results in further distance between the valence electron and thenucleus. In addition, the increase in number of electrons in the inner shellsalso increases the shielding effect. These factors cause the valence electronsto be less attracted to the nucleus and requires lower amount of energy toremove the first electron from the valence shell.

ii. The second ionization energy is usually higher than the first ionizationEnergy

Model answers: Rui Jin’s: The element has more protons than electrons. The nuclear charge increases,the attractive force increases, it is harder to remove another electron so ithas higher ionization

Recommended answers: As the first electron is removed, there is a higher amount of nuclear chargedue to higher number of proton than its electrons. Thus its relativeattraction force is higher and requires higher amount of energy to removethe second electron from the valence shell.

13. Figure below shows the energy required to remove ten electrons, one at a time, from

an atom of element X.



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Min Si’s: This is because the 6th electron is the last electron in the outermost shell of elementX, the 7th electron is the electron in the inner shell. The 5

th& 6

thelectron are in the

same shell which is the outermost occupied shell. More energy is required toremove the 7th electron because the attraction force between nucleus and theelectron is stronger.

Harvind’s and Matthew’s: The removal of the 6

th& 7

thelectrons involves different shells. The energy is higher

when the ionization takes place from one shell to another moving from outwards toinwards. Meanwhile the 5

th& 6

thelectron removal is much lower because it involves

the same shell which doesn’t consume much energy

Ronson’s: The energy difference between the 6th & 7th ionization is larger than the 5th & 6th ionization becausethey are taking place at different shells. At the 6th ionisation, the

process is still taking place at the outermost shell but the 7 th

ionization takes place atthe next shell nearer to nucleus.

Recommended answers:The removal of the 7th electron involves an inner shell while the removal of the 5th and 6th electrons involves the same valence shell. Thus, more energy is required toremove the 7th electron which is more attracted to the nucleus, causes a bigionization energy difference between the 6th and 7th electrons than the ionizationenergy difference between the 5th and 6th electrons

i o n i z a t i o n e n e r g y

, k J / m o l

a. Which group in the Periodic Table doeselement X belongs?

Group 6 (VI) b. What is the outer electronic configuration

for X?

s2p4 c. Why is the energy difference between the

removal of the 6th

and 7th

electrons muchlarger than the energy difference between

the removal of the 5th

and 6th

electrons?

Model answers: Joy’s: This is because the 6th & 7th electronsare in different shells. The 7

thelectron is in a shell

which is closer to the nucleus compared tothat which is occupied by the 6th electron.The 5

th& 6

thelectrons occupy the same

shell. This is why there is only a gradualincrease in ionisation energywhile there is a big difference in ionization energybetween the 6th and 7th electrons



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a. Name one element that could be the element X and write its full electronic

configurations

Oxygen 1s22s22p4 Sulfur 1s22s22p63s23p6

or any group VI elements

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