Trends in Group II (Alkali Earth Metals) Elements |
Properties of Group IIA Elements |
| Period |
Name
(Symbol) |
Atomic Number (Z) |
Simple Electronic Configuration |
Atomic Radius
(picometres) |
First
Ionization Energy(kJ/mol) |
Second
Ionization Energy(kJ/mol) |
Third
Ionization Energy(kJ/mol) |
Melting point (oC) |
Density (g/cm3) |
Electro-
negativity |
| 2 |
Beryllium
(Be) |
4 |
2,2 |
112 |
899 |
1757 |
14,849 |
1280 |
1.86 |
1.5 |
|
| 3 |
Magnesium
(Mg) |
12 |
2,8,2 |
160 |
738 |
1450 |
7730 |
651 |
1.75 |
1.2 |
|
| 4 |
Calcium
(Ca) |
20 |
2,8,8,2 |
197 |
590 |
1145 |
4941 |
851 |
1.55 |
1.0 |
|
| 5 |
Strontium
(Sr) |
38 |
2,8,18,8,2 |
215 |
549 |
1064 |
4207 |
800 |
2.6 |
1.0 |
|
| 6 |
Barium
(Ba) |
56 |
2,8,18,18,8,2 |
217 |
503 |
965 |
3420 |
850 |
3.6 |
0.9 |
|
| 7 |
Radium
(Ra) |
88 |
2,8,18,32,18,8,2 |
|
509 |
978 |
|
960 |
5.0 |
0.9 |
| |
| | |
Trends in Properties of Group II Elements |
- all Group II metals have 2 valence electrons (2 electrons in the highest energy level)
- atomic radius increases down the Group as successive 'electron shells' (energy levels) are filled
- down the Group, first ionization energy (the energy required to remove 1 electron from the gaseous atom) decreases. As the atomic radius increases and the electron is further from the nucleus it is less attracted to the nucleus (electron is said to be 'shielded')
- down the Group, second ionization energy (the energy required to remove an electron from the gaseous positive ion) decreases. As successive electron 'shells' (energy levels) are filled, the electron is further from the positively charged nucleus, and therefore less attracted to it, making the electron easier to remove.
- down the Group, third ionization decreases (the energy required to remove an electron from the gaseous ion of charge 2+). As succcessive electron 'shells' (energy levels) are filled, the electron is further from the positively charged nucleus, and therefore less attracted to it, making the electron easier to remove.
- second ionization energy is higher than the first ionization for each element. This is because it is harder to remove the electron since there are more positive charges (protons) in the nucleus than there are negative charges (electrons in 'shells'), hence the electron's attraction to the nucleus is greater.
- third ionization energy is substantially higher than the second ionization energy. When 2 electrons have been removed from the gaseous atom, the remaining electrons are arranged like a noble gas which is a VERY stable electron configuration. It is very difficult to remove an electron from this arrangement.
- In general, electronegativity decreases down the Group as successive energy levels (electron shells) are filled, the positive nucleus exerts less force on electrons and so has less ability to attract electrons.
- melting point decreases down the Group as the elements become less metallic in nature
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