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## End of chapter exercises

For the following questions state whether they are true or false. If they are false, correct the statement

1. The group 1 elements are sometimes known as the alkali earth metals.

2. The group 8 elements are known as the noble gases.

3. Group 7 elements are very unreactive.

4. The transition elements are found between groups 3 and 4.

a) False. The group 1 elements are sometimes known as the alkali metals.

b) True

c) False. Group 7 elements are very reactive.

d) False. The transition elements are found between groups 2 and 3.

Give one word or term for each of the following:

1. The energy that is needed to remove one electron from an atom

2. A horizontal row on the periodic table

3. A very reactive group of elements that is missing just one electron from their outer shells.

a) Ionization energy

b) Period

c) Halogens (group 17)

Given $​3580Br$ and $​1735Cl$. Compare these elements in terms of the following properties. Explain the differences in each case.

2. Electronegativity

3. First ionisation energy

4. Boiling point

1. Bromine has a larger atomic radius than chlorine. Bromin has more electrons than chlorine and is filling an extra energy level. This increases the atomic radius.
2. Chlorine has a higher electronegativity than bromine. As you move down a group the valence electrons are further away from the nucleus and so experience less attraction from the nucleus. This decreases the elements pull on the electrons (electronegativity).
3. Chlorine has a higher first ionisation energy than bromine. As you move down a group, the outermost electrons are further away from the nucleus and are not held as tightly. This makes the ionisation energy higher for atoms at the top of a group.
4. Chlorine has a higher boiling point than bromine. Magnesium has stronger forces holding its atoms together and so more energy is needed to make magnesium boil.

Given the following table:

Table 1
 Element $Na$ $Mg$ $Al$ $Si$ $P$ $S$ $Cl$ $Ar$ Atomic number 11 12 13 14 15 16 17 18 Density (g·cm−3) 0,97 1,74 2,70 2,33 1,82 2,08 3,17 1,78 Melting point (℃) 370,9 923,0 933,5 1687 317,3 388,4 171,6 83,8 Boiling point (℃) 1156 1363 2792 3538 550 717,8 239,1 87,3 Electronegativity 0.93 1.31 1.61 1.90 2.19 2.58 3.16 -

Draw graphs to show the patterns in the following physical properties:

1. Density

2. Boiling point

3. Melting point

4. Electronegativity

A graph showing the pattern in first ionisation energy for the elements in period 3 is shown below:

1. Explain the pattern by referring to the electron configuration

2. Predict the pattern in the first ionisation energy for the elements in period 2.

3. Draw a rough graph to show the pattern predicted in the previous question.

1. As you move across a period the first ionisation energy increases. This is because we are adding an electron every time we increase atomic number. As we move closer to filling the outermost shell the element would rather gain electrons than lose them and this is seen in the higher ionisation energies.
2. The pattern should be the same.