Periodicity

Periodicity

Periodicity is the study of the repeating patterns or trends that occur in physical or chemical properties as we move around in the periodic table. These physical and chemical properties are typically linked to the whereabouts in the periodic table we find particular elements.

Position in the Periodic Table

To describe an element's position in the periodic table, we use the following terms:

• Groups: columns of the periodic table

• Periods: rows of the periodic table

• Blocks: regions of the periodic table that correspond to the subshell where the outer electrons are found The main blocks are: | Block | Subshell | Elements | | --- | --- | --- | | s block | s subshell | Group 1 and 2 elements | | p block | p subshell | Right-hand side of the periodic table (last 6 groups) | | d block | d subshell | Transition elements (middle of the periodic table) |

Atomic Radius

The atomic radius is the distance between the center of the atom (the nucleus) and the electrons in the outermost energy level.

As we move across period 3, the atomic radius decreases due to the increasing nuclear charge (number of protons) and the same electron shielding for each element. This results in a stronger electrostatic attraction between the nucleus and the outer shell electrons, pulling them closer to the nucleus.

Electronegativity

Electronegativity is the ability of an atom to attract electron density or simply electrons in a covalent bond.

The pattern of electronegativity across period 3 is an increase, as the electrons are more attracted to the nucleus due to the increasing nuclear charge and decreasing atomic radius. The electronegativity pattern can be summarized as follows:

• Increases across a period (from left to right)

• Increases up a group (from bottom to top) The most electronegative elements are found at the top right of the periodic table, while the least electronegative elements are found at the bottom left.

Ionization Energy

Ionization energy is the enthalpy or energy required to remove a mole of electrons from a mole of gaseous atoms.

The pattern of ionization energy across period 3 will be discussed in relation to the atomic radius and electronegativity trends. Key points to note:

• Ionization energy is related to the atomic radius and electronegativity of an element

• The pattern of ionization energy across a period is typically an increase, due to the increasing nuclear charge and decreasing atomic radius.## Ionization Energy The ionization energy is the energy change needed to remove a mole of electrons from a mole of gaseous atoms. This energy change is exactly equal to the ionization energy for an element.

The ionization energy for an element depends on the attraction between the nucleus and the electrons. The stronger the attraction, the harder it is to remove an electron, and therefore the larger the ionization energy.

Factors Affecting Ionization Energy

The ionization energy is affected by the following factors:

• The distance between the electrons and the nucleus: The closer the electrons are to the nucleus, the stronger the attraction and the larger the ionization energy.

• The nuclear charge: The larger the nuclear charge, the stronger the attraction between the nucleus and the electrons, and the larger the ionization energy.

Pattern of Ionization Energy Across a Period

The ionization energy generally increases across a period, but there are dips in the pattern. The reasons for these dips are:

• The electron configuration of the elements: The ionization energy is lower for elements with electrons in the p subshell than for elements with electrons in the s subshell.

• The repulsion between electrons: When there are multiple electrons in the same orbital, they repel each other, making it easier to remove one of the electrons.

Ionization Energy Pattern Across Period 3

The pattern of ionization energy across period 3 is as follows:

The dips in the pattern occur between:

• Magnesium and Aluminium: Due to the change from s subshell to p subshell.

• Phosphorus and Sulfur: Due to the repulsion between electrons in the p subshell.

Ionization Energy Trend Down a Group

As you go down a group, the ionization energy decreases due to the increase in distance between the electrons and the nucleus. This results in a smaller ionization energy because the electrons are easier to remove.

States of Matter

The three states of matter are:

• Solids: Atoms are closely packed and have a regular structure.

• Liquids: Atoms are close together but have a more random structure.

• Gases: Atoms are far apart and have a lot of energy.

The melting and boiling points of elements are related to the strength of the intermolecular forces between the atoms. The stronger the intermolecular forces, the higher the melting and boiling points.## Melting and Boiling Points The melting point is the temperature at which a solid turns into a liquid, and it is also the temperature at which a liquid turns into a solid. This occurs when the solid particles have enough energy to move slightly away from each other and overcome the forces that exist between the particles in the solid structure.

The boiling point is the temperature at which a liquid turns into a gas. If the liquid particles have strong forces between each other, it will be hard to separate them, and lots of energy will be required, resulting in a higher boiling point.

Factors Affecting Melting and Boiling Points

The following factors affect the melting and boiling points of a substance:

• Type of bonding: The type of bonding between particles, such as metallic bonding, covalent bonding, or van der Waals forces, affects the melting and boiling points.

• Strength of forces: The strength of the forces between particles affects the melting and boiling points. Stronger forces result in higher melting and boiling points.

• Size of particles: The size of the particles affects the melting and boiling points. Larger particles have weaker van der Waals forces, resulting in lower melting and boiling points.

Periodic Trends

The melting points of elements in period 3 can be explained by the type of bonding and the strength of forces between particles. The elements can be divided into three regions:

Metallic Bonding

Metallic bonding occurs in metals, where the outer electrons are delocalized and free to move through the structure. This results in a strong electrostatic attraction between the metal ions and the delocalized electrons.

Giant Covalent Bonding

Giant covalent bonding occurs in giant covalent structures, such as silicon, where each atom is bonded to its neighbors through strong covalent bonds. This results in a very high melting point due to the large amount of energy required to break these bonds.

Simple Molecular Bonding

Simple molecular bonding occurs in simple molecular substances, such as phosphorus, sulfur, and chlorine, where the molecules are held together by weak van der Waals forces. The melting point of these substances is affected by the size of the molecules and the number of electrons.

Monoatomic Bonding

Monoatomic bonding occurs in noble gases, such as argon, where the atoms are not strongly attracted to each other and are held together by weak van der Waals forces. This results in a very low melting point due to the weak forces between the atoms.## Periodic Trends and Properties The periodic trends of elements can be explained by analyzing the forces between molecules. When comparing the melting points of two elements, the one with the stronger forces will have a higher melting point. For example, phosphorus has a higher melting point than chlorine because it is a larger molecule with stronger van der Waals forces, which require more energy to overcome.

Factors Affecting Melting and Boiling Points

The boiling points of elements follow the same pattern as melting points, with boiling point values being greater than melting point values. The justification for these patterns can be explained by considering the forces between molecules and the energy required to overcome them.

Key Concepts and Skills

To master this topic, students should be able to:

• Define periodicity, electronegativity, and ionization energy

• State the block an element is in based on its position in the periodic table

• Work with graphs to complete and analyze data for atomic radius, electronegativity, first ionization energy, and melting point

• Explain patterns in these properties as they relate to period three and other periods

• Apply these rules to different periods and elements

Key Properties and Trends

The following properties and trends are essential to understanding this topic:

Applying Periodic Trends

To apply periodic trends to different elements and periods, students should be able to:

• Analyze the forces between molecules and the energy required to overcome them

• Explain patterns in melting point, boiling point, and other properties

• Apply these rules to different periods and elements, even if they have not been studied in class.