Chemistry · Chapter 9
Study notes aligned to the official NEB syllabus.
Non-metals are elements that tend to gain or share electrons; they are electronegative, poor conductors, and form acidic or neutral oxides. This chapter surveys the important non-metals of the NEB syllabus: hydrogen, oxygen and ozone, nitrogen (with ammonia and nitric acid), the halogens, carbon, phosphorus and sulphur, along with their key preparations, properties, tests and uses. Every equation below is balanced and written in mhchem.
Hydrogen ($\ce{H}$, $Z=1$) is the lightest element. It shows similarities to both group 1 metals (one valence electron) and group 17 halogens (one electron short of a stable configuration), so its position is anomalous.
Hydrogen has three isotopes: protium ($\ce{^1H}$, no neutron), deuterium ($\ce{^2H}$ or $\ce{D}$, one neutron) and tritium ($\ce{^3H}$ or $\ce{T}$, two neutrons, radioactive). They have the same chemical properties but differ in mass.
Hydrogen burns cleanly, giving only water and a large amount of energy:
$$\ce{2H2(g) + O2(g) -> 2H2O(l)} \qquad \Delta H = -572\ \text{kJ}$$
It is a promising clean fuel (in fuel cells and rockets) because it produces no carbon dioxide; challenges are safe storage and transport of a light, flammable gas.
Heavy water is deuterium oxide, $\ce{D2O}$. It is obtained by prolonged electrolysis of ordinary water (which decomposes $\ce{H2O}$ faster than $\ce{D2O}$). It has a higher boiling point ($\ce{101.4 ^\circ C}$) and density than ordinary water. Uses: as a moderator in nuclear reactors (to slow neutrons) and in tracer studies.
Oxygen ($\ce{O}$, $Z=8$) is the most abundant element in the Earth's crust and is essential for respiration and combustion.
Oxygen has two allotropes: ordinary dioxygen ($\ce{O2}$) and ozone ($\ce{O3}$).
Oxygen is prepared in the laboratory by heating potassium chlorate with a $\ce{MnO2}$ catalyst:
$$\ce{2KClO3(s) ->[\Delta][MnO2] 2KCl(s) + 3O2(g)}$$
It is a colourless, odourless gas that supports combustion; it reacts with metals and non-metals to form oxides, e.g.
$$ \ce{S(s) + O2(g) -> SO2(g)} $$
and
$$ \ce{2Mg(s) + O2(g) -> 2MgO(s)} $$
.
Non-metals are elements that tend to gain or share electrons; they are electronegative, poor conductors, and form acidic or neutral oxides. This chapter surveys the important non-metals of the NEB syllabus: hydrogen, oxygen and ozone, nitrogen (with ammonia and nitric acid), the halogens, carbon, phosphorus and sulphur, along with their key preparations, properties, tests and uses. Every equation below is balanced and written in mhchem.
Hydrogen (, ) is the lightest element. It shows similarities to both group 1 metals (one valence electron) and group 17 halogens (one electron short of a stable configuration), so its position is anomalous.
Hydrogen has three isotopes: protium (, no neutron), deuterium ( or , one neutron) and tritium ( or , two neutrons, radioactive). They have the same chemical properties but differ in mass.
Hydrogen burns cleanly, giving only water and a large amount of energy:
It is a promising clean fuel (in fuel cells and rockets) because it produces no carbon dioxide; challenges are safe storage and transport of a light, flammable gas.
Heavy water is deuterium oxide, . It is obtained by prolonged electrolysis of ordinary water (which decomposes faster than ). It has a higher boiling point () and density than ordinary water. Uses: as a moderator in nuclear reactors (to slow neutrons) and in tracer studies.
Oxygen (, ) is the most abundant element in the Earth's crust and is essential for respiration and combustion.
Oxygen has two allotropes: ordinary dioxygen () and ozone ().
Oxygen is prepared in the laboratory by heating potassium chlorate with a catalyst:
It is a colourless, odourless gas that supports combustion; it reacts with metals and non-metals to form oxides, e.g.
and
.