Atomic Structure, Bonding and the Periodic Table. Revision questions.

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Task 1: Atomic Structure

1.  Copy and complete this table:

2. Describe how 12C and 13C are different and how they are the same. You should include the different types of sub-atomic particles in your answer. What term is used to describe how these two atoms are related?

12C and 13C are isotopes of carbon, like most elements carbon has several isotopes. It is the number of protons (atomic number Z) which defines a specific element, and so carbon-12 and carbon-13 are still distinct as the element carbon, as they each have 6 protons (atomic number Z = 6). Both the 12C and 13C isotopes also still have the same electronic configuration, with 6 electrons in total, meaning that they are identical in how they react chemically. The reason for the categorisation as isotopes of carbon is because their atomic mass is different, with carbon-12 possessing 6 neutrons and carbon-13 possessing 7 neutrons.

3. For each of the following species, give a full electronic configuration in the format 1s2, 2s2,

 a) Sodium - 1s2, 2s2, 2p6, 3s1

b) Chlorine - 1s2, 2s2, 2p6, 3s2, 3p5

c) Carbon - 1s2, 2s2, 2p2

d) Ni+2 (Nickel cation) - 1s2, 2s2, 2p6, 3s2, 3p6, 3d8

e) Calcium - 1s2, 2s2, 2p6, 3s2, 3p6, 4s2

f) Chromium - 1s2, 2s2, 2p6, 3s2, 3p6, 4s1, 3d5

g) Bromide ion (Br -) - 1s2, 2s2, 2p2, 3s2, 3p6, 4s2, 3d10, 4p6

h) Al+3 (aluminium cation) - 1s2, 2s2, 2p6

4. The following questions relate to the graph below:

Figure 1: First ionisation energy of the 1st 20 elements

a. Write an equation for the first ionisation energy of sodium.

Na (g)         Na+(g) + e-  

b. Why is there a large drop in ionisation energy between helium and lithium?

If we look at the electronic configuration of the two species it becomes apparent that lithium has and additional electron, (He – 1s2 and Li – 1s2, 2s1). Although the nuclear charge is greater in lithium, which has an extra proton, the effective nuclear charge is less. This is because the attractive force exerted on the 2s electron is reduced because of its increased distance from the atomic nuclei, and the shielding effect of the 1s orbital, meaning less energy is needed to remove it.

c. Why is there a general upward trend in the ionisation energy between lithium and neon?

Because from left to right across the period there are additional protons present in the nucleus, which raises the nuclear charge. At the same electrons are still filling the 2nd energy level so there is no increase in distance or shielding. As such the effective nuclear charge is greater, causing a rise in ionisation energy between lithium and neon.

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d. Why does the ionisation energy drop between beryllium and boron?

The slightly lower ionisation energy of boron occurs because the extra electron has filled the 2p1 sub-shell and is being shielded by the 1s and 2s orbital’s, reducing the effective nuclear charge and lowering the energy required to remove the electron.

e. Why does the ionisation energy drop between nitrogen and oxygen?

The additional electron in oxygen has filled the 2pX2 sub-orbital which is already occupied. Because electrons exert a repulsive force on each other less energy is required to remove this electron. (it was this drop in ionisation ...

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