Nomenclature and Identity
Element list: Period 3 of the periodic table contains eight elements: sodium (Na), magnesium (Mg), aluminium (Al), silicon (Si), phosphorus (P), sulfur (S), chlorine (Cl), and argon (Ar). These elements are arranged from left to right in a row based on increasing atomic number.
Metallic to Non-Metallic Trend
Left to right transition: As we move from the left side to the right side of Period 3, the elements gradually change from metals to non-metals. This means their properties shift from metallic (like being shiny and good at conducting electricity) to non-metallic (like being dull and not conducting electricity well).
Metal elements: The first three elements in Period 3—sodium, magnesium, and aluminium—are considered metals. These elements are shiny, can conduct heat and electricity, and are malleable, meaning they can be shaped without breaking.
Metalloid element: Silicon is in the middle and is called a metalloid. It has some metallic properties and some non-metallic properties. For example, it conducts electricity but not as well as metals.
Non-metal elements: Phosphorus, sulfur, and chlorine are non-metals. They do not conduct electricity, and they can be brittle or gases at room temperature.
Noble gas: Argon is the last element in the period. It is a noble gas, which means it is unreactive and doesn’t usually form compounds with other elements because it already has a full outer shell of electrons.
Physical Properties
States at room temperature: Most of the Period 3 elements—like sodium, magnesium, aluminium, silicon, phosphorus, and sulfur—are solids at room temperature. However, chlorine is a yellow-green gas, and argon is a colorless gas.
Melting/boiling trends: The melting points of the elements increase from sodium to silicon, which means they require more heat to change from solid to liquid. After silicon, the melting points drop as we move to phosphorus, sulfur, chlorine, and argon. The boiling points show a similar pattern.
Electrical Conductivity
Metal conductors: The metals (sodium, magnesium, and aluminium) conduct electricity very well because their electrons can move freely.
Silicon’s conductivity: Silicon does not conduct electricity as well as metals, but it still conducts a little, especially when heated or combined with other elements. That’s why it is called a semiconductor and is used in electronic devices.
Non-metal insulators: Phosphorus, sulfur, and chlorine are poor conductors of electricity. They are called insulators because they do not let electric current pass through easily.
Argon non-conductive: Argon, being a noble gas, does not conduct electricity at all because its electrons are tightly held and don’t move freely.
Atomic Radius
Decreasing size: As you go across Period 3 from left to right, the atoms get smaller. This is because the number of protons in the nucleus increases, which pulls the electrons in closer. Even though more electrons are being added, they go into the same energy level, so the size shrinks.
Ionization Energy
Increasing energy: Ionization energy is the energy needed to remove an electron from an atom. This energy increases from left to right in Period 3 because the atoms hold on to their electrons more tightly due to stronger attraction from the increasing number of protons.
Electronegativity
Stronger attraction: Electronegativity means how strongly an atom attracts electrons in a bond. As you go from left to right in Period 3, electronegativity increases because the atoms have more protons and a smaller size, so they can pull electrons more strongly.
Chemical Properties
Reactions with Oxygen
Oxide formation: All Period 3 elements can react with oxygen to form oxides, which are compounds that contain oxygen and one other element.
Basic oxides: Sodium oxide (Na₂O) and magnesium oxide (MgO) are called basic oxides. When they dissolve in water, they form alkaline solutions.
Amphoteric oxide: Aluminium oxide (Al₂O₃) is special because it can act like both an acid and a base. This kind of substance is called amphoteric.
Acidic oxide – Silicon: Silicon reacts with oxygen to form silicon dioxide (SiO₂), which is acidic and does not dissolve easily in water.
Acidic oxides – Non-metals: The non-metal elements phosphorus, sulfur, and chlorine react with oxygen to form acidic oxides such as phosphorus pentoxide (P₄O₁₀), sulfur dioxide (SO₂), and dichlorine heptoxide (Cl₂O₇). These oxides can form acids when mixed with water.
Reactions with Water
Sodium and magnesium: These two metals react with water, but not very quickly. Sodium reacts faster than magnesium and produces hydrogen gas.
Aluminium: Aluminium does not react with cold water because it forms a protective oxide layer on its surface, which prevents further reaction.
Silicon, phosphorus, sulfur: These three elements do not react with water at all.
Chlorine reaction: Chlorine dissolves in water and reacts to form a mixture of hydrochloric acid (HCl) and chloric(I) acid (HOCl), which is also called hypochlorous acid.
Reactions with Acids and Alkalis
Metal oxides with acids: The metal oxides of sodium and magnesium react with acids to produce a salt and water, which is a neutralization reaction.
Amphoteric oxide reactions: Aluminium oxide can react with both acids and alkalis, showing its amphoteric nature. It forms different compounds depending on the substance it reacts with.
Non-metal oxides with alkalis: The oxides made by silicon, phosphorus, sulfur, and chlorine are acidic, so they can react with alkalis to form salts and water.
Reactivity
Metal reactivity trend: In Period 3, the metals on the left side (like sodium) are more reactive than those further to the right (like aluminium). This is because the outer electrons of elements on the left are easier to lose.