Periodic Properties and Their Variations - SS2 Chemistry Lesson Note

Periodic properties are characteristics or properties of elements that exhibit a periodic trend or pattern across the periodic table. Here are some important periodic properties and their variations:

Atomic Radius:

●     Atomic radius refers to the size of an atom, specifically the distance between the nucleus and the outermost electron shell.

●     Across a period (from left to right), atomic radius generally decreases. This is because the increasing number of protons in the nucleus leads to a stronger effective nuclear charge, pulling the electrons closer and reducing the atomic size.

●     Down a group (from top to bottom), atomic radius generally increases. This is because each subsequent element adds a new energy level or shell, increasing the distance between the nucleus and the outermost electrons.

Ionization Energy:

●     Ionisation energy is the energy required to remove an electron from an atom or ion in the gaseous state.

●     Across a period, ionisation energy generally increases. This is because the increasing effective nuclear charge attracts the electrons more strongly, making it more difficult to remove them.

●     Down a group, ionisation energy generally decreases. This is due to the increasing distance between the valence electrons and the nucleus, resulting in weaker attraction and lower ionisation energy.

Electronegativity:

●     Electronegativity is the ability of an atom to attract shared electrons in a covalent bond.

●     Across a period, electronegativity generally increases. This is because the increasing effective nuclear charge enhances the atom's ability to attract electrons.

●     Down a group, electronegativity generally decreases. This is mainly due to the increasing atomic size and the shielding effect of inner electrons, which reduce the attractive force on shared electrons.

Electron Affinity:

●     Electron affinity is the energy change that occurs when an atom gains an electron to form a negatively charged ion.

●     Across a period, electron affinity can increase or decrease. The elements on the right side of the periodic table tend to have higher electron affinities as they are closer to achieving a stable noble gas electron configuration.

●     Down a group, electron affinity generally decreases. This is because the increasing atomic size and shielding effect reduce the effective nuclear charge, resulting in a weaker attraction for additional electrons.

Metallic Character:

●     Metallic character refers to the tendency of an element to exhibit metallic properties such as metallic lustre, conductivity, and malleability.

●     Across a period, a metallic character generally decreases. This is due to the increasing effective nuclear charge, which strengthens the attraction between the nucleus and the valence electrons, making it more difficult for the electrons to move freely and exhibit metallic behaviour.

●     Down a group, a metallic character generally increases. This is because the increasing atomic size and the presence of more energy levels allow the valence electrons to move more freely, enhancing metallic properties.