Periodic Trends

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CSEC CHEMISTRY
NOTES ON PERIODIC TRENDS
From Chemistry for CSEC by Tania Chung-Harris and Mike Taylor
Chemistry for CAPE by Susan Maraj and Arnold Samai

Periodic Trends in Group II

Elements in Group II
The elements in Group II are called alkaline earth metals.
Be, Mg, Ca, Sr, Ba, Ra
Beryllium, Magnesium, Calcium, Strontium, Barium, Radium

These elements bond by metallic bonds (intramolecular forces) to form giant metallic structures.

The size of the atoms increases down the group

Physical properties of Group II metals

Ionization
The process of removing an electron from an isolated atom (or an ion) to form a cation. First ionization:M(g) M+(g) + 1e-
Second ionization:M+ (g) M2+(g) + 1e-

Ease of ionization
All the Group II elements have two electrons in their outer shell. They can lose these electrons to form positive ions. e.g. Ca Ca2+ + 2e-

In the neutral atoms the electrons are held to the nucleus by the electrostatic attraction of the protons in the nucleus. The further the electrons are away from the nucleus, the more weakly they are held. First and second ionization energies are the energies required to remove the first and second electron respectively.

The larger the Group II atom, the smaller the ionization energies. The larger the atom, the easier it is to ionize it.

Reactivity
The reactivity of Group II elements depends on their ease of ionization. Reactivity of Group II INCREASE down the group.

Reactivity with oxygen

Magnesium metal + oxygen gas magnesium oxide
Mg (s) + O2 (g) MgO (s)unbalanced
2Mg (s) + O2 (g) 2MgO (s)balanced

Calcium metal + oxygen gas calcium oxide
Ca (s) + O2 (g) CaO (s)unbalanced
2Ca (s) + O2 (g) 2CaO (s)balanced

Barium metal + oxygen gas barium oxide
Ba (s) + O2 (g) BaO (s)unbalanced
2Ba (s) + O2 (g) 2BaO (s)balanced

Read:Chemistry for CSEC by Tania Chung-Harris and Mike Taylor
Page 68
Copy available during consultation times

Reactivity with water

Magnesium metal + cold water magnesium hydroxide + hydrogen gas Mg (s) + H2O (l) Mg(OH)2 (aq) + H2 (g)unbalanced Mg (s) + 2H2O (l) Mg(OH)2 (aq) + H2 (g) (very slow reaction) balanced

Magnesium metal + steam magnesium oxide + hydrogen gas Mg (s) + H2O (g) MgO (s) + H2 (g) balanced

Calcium metal + cold water calcium hydroxide + hydrogen gas Ca (s) + H2O (l) Ca(OH)2 (s) + H2 (g) unbalanced Ca (s) + 2H2O (l) Ca(OH)2 (s) + H2 (g) balanced

Barium metal + cold water barium hydroxide + hydrogen gas Ba (s) + H2O (l) Ba(OH)2 (aq) + H2 (g) unbalanced Ba (s) + 2H2O (l) Ba(OH)2 (aq) + H2 (g) balanced

Reactivity with dilute hydrochloric acid
Magnesium metal + hydrochloric acid magnesium chloride + hydrogen gas Mg (s) + HCl (aq) MgCl2 (aq) + H2 (g) unbalanced Mg (s) + 2HCl (aq) MgCl2 (aq) + H2 (g) balanced

Calcium metal + hydrochloric acid calcium chloride + hydrogen gas Ca (s) + HCl (aq) CaCl2 (aq) + H2 (g) unbalanced Ca (s) + 2HCl (aq) CaCl2 (aq) + H2 (g) balanced

Barium metal + hydrochloric acid barium chloride + hydrogen gas Ba (s) + HCl (aq) BaCl2 (aq) + H2 (g) unbalanced Ba (s) + 2HCl (aq) BaCl2 (aq) + H2 (g) (Explosive. do not try this)

Periodic Trends in Group VII

Elements in Group VII
The elements in Group VII are called halogens
The atoms are:F, Cl, Br, I, At
The...
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