Inorganic - Properties of Period 3 Elements and their Oxides Flashcards
What is the physical trend in period 3 elements from metals on the left to non-metals on the right?
- Sodium, magnesium and aluminium are metallic. They are shiny (when freshly exposed to air), conduct electricity, and react with dilute acids to give hydrogen and salts.
- Silicon is a semi-metal (or metalloid). It conducts electricity to some extent, a property that is useful in making semiconductor devices.
- Phosphorus, sulphur, and chlorine are typical non-metals. In particular, they do not conduct electricity and have low melting and boiling points. S8 molecule is larger than P4 and Cl2, so more electrons and stronger van der Waals forces, requiring more energy to overcome so higher melting point.
- Argon is a noble gas. It is chemically unreactive and exists as separate atoms.
What type of reactions do elements in period 3 undergo?
The reactions of all the elements in period 3 are all redox reactions, since every element starts with an oxidation state of zero, and (after it has reacted) ends up with a positive or a negative oxidation state. The oxidation state of the metal increases and that of some of the hydrogen atoms decreases.
Which elements in group 3 react with water?
Sodium and magnesium are the only metal elements in period 3 that react with cold water. Chlorine is the only non-metal that reacts with water.
What is the reaction of sodium with water?
The reaction of sodium with water is vigorous - the sodium floats on the surface of the water and fizzes rapidly, melting because of the heat energy released by the reaction. A strongly alkaline solution of sodium hydroxide is formed (pH 13-14).
2Na + 2H2O -> 2NaOH + H2
What is the reaction of magnesium with water?
The reaction of magnesium is very slow at room temperature, only a few bubbles of hydrogen are formed after some days. The resulting solution is less alkaline than in the case of sodium because magnesium hydroxide is only sparingly soluble (pH around 10).
Mg + 2H2O -> Mg(OH)2 + H2 (slow release of bubbles)
The reaction is much faster with heated magnesium and steam and gives magnesium oxide and hydrogen. Steam provides the reaction with greater energy, resulting in a violent reaction in which magnesium burns with a bright white flame, and a white powder is formed.
Mg + H2O -> MgO + H2
Which elements in group 3 react with oxygen?
All the elements in period 3 (except for argon) are relatively reactive. Their oxides can all be prepared by direct reaction of the element with oxygen. The reactions are exothermic.
The period 3 elements react with oxygen to form oxides with each element in their highest oxidation state. This number is often the same as the group number.
What is the reaction of sodium with oxygen?
Sodium burns brightly in air (with a characteristic yellow flame) to form white sodium oxide. The sodium formed may have a yellowish appearance due to the production of some sodium peroxide (Na2O2).
4Na + O2 -> 2Na2O
What is the reaction of magnesium with oxygen?
A strip of magnesium ribbon burns in air with a bright white flame. The white powder that is produced is magnesium oxide. If burning magnesium is lowered into a gas jar of oxygen, the flame is even more intense.
2Mg + O2 -> 2MgO
The oxidation states show how magnesium has been oxidised (its oxidation state has increased) and oxygen has been reduced (its oxidation number has decreased).
What is the reaction of aluminium with oxygen?
When aluminium powder is heated and then lowered into a gas jar of oxygen, it burns brightly to give aluminium oxide - a white powder. Aluminium powder also burns brightly in air.
4Al + 3O2 -> 2Al2O3
Aluminium is a reactive metal, but it is always coated with a strongly bonded surface layer of oxide - this protects it from further reaction. So, aluminium appears to be an unreactive metal and is used for many everyday purposes (saucepans, window frames etc.). Even if the surface is scratched, the exposed aluminium reacts rapidly with the air and seals off the surface.
What is the reaction of silicon with oxygen?
Silicon will also form the oxide if it is heated strongly in oxygen. Again, there’s a bright white flame and a white solid is formed.
Si + O2 -> SiO2
What is the reaction of phosphorus with oxygen?
Red phosphorus must be heated before it will react with oxygen. White phosphorus spontaneously ignites in air and the white smoke of phosphorus pentoxide is given off. Red and white phosphorus are allotropes of phosphorus - the same element with the atoms arranged differently.
4P + 5O2 -> P4O10
If the supply of oxygen is limited, phosphorus trioxide (P2O3) is also formed.
What is the reaction of sulphur with oxygen?
When sulphur powder is heated and lowered into a gas jar of oxygen, it burns with a blue flame to form the colourless gas sulphur dioxide (and a little sulphur trioxide also forms). To produce sulphur trioxide, high temperatures and a catalyst are required. A choking gas is formed.
S + O2 -> SO2
2S + 3O2 -> 2SO3
What happens to the oxidation states in all redox reactions of the period 3 elements?
In all the redox reactions, the oxidation state of the period 4 element increases and that of the oxygen decreases (from 0 to -2). The oxidation number of the period 3 element in the oxide increases as you move from left to right across the period.
What are the properties of metal oxides?
Sodium, magnesium, and aluminium oxides are examples of compounds formed by a metal combined to a non-metal. They form giant ionic lattices where the bonding extends throughout the compound. This results in high melting points.
The bonding in aluminium oxide is ionic but has some covalent character. This is because aluminium forms a very small ion with a large positive charge and so can approach closely to the O 2- and distort its electron cloud. So the bond also has some added covalent character. This means Al2O3 has a lower melting point than MgO.
How can you predict ionic character?
It is possible to predict the ionic character of a bond by considering the difference in electronegativities between the two atoms. The bigger the difference, the greater the ionic character of the bond. The smaller the difference, the greater the covalent character.
(large difference) - ionic bonding - distorted ionic bonding - polar covalent - pure covalent (small difference)
