Chemistry Revision: Structure and Trends of the Periodic Table PDF

# Chemistry revision ## 1. Structure and Trends of the Periodic Table ### Organization of the Periodic Table The periodic table is organized primarily by atomic number, which is the number of protons in an atom's nucleus. Elements are arranged in periods (horizontal rows) and groups (vertical col...

# Chemistry revision ## 1. Structure and Trends of the Periodic Table ### Organization of the Periodic Table The periodic table is organized primarily by atomic number, which is the number of protons in an atom's nucleus. Elements are arranged in periods (horizontal rows) and groups (vertical columns), reflecting their chemical properties and electron configurations. The layout allows for the identification of trends in element properties, such as reactivity and ionization energy. ### Trends Across Periods and Groups - **Atomic Radii:** Atomic size decreases across a period due to increasing nuclear charge, which pulls electrons closer to the nucleus. Conversely, atomic size increases down a group as additional energy levels are added. - **Valency:** The valency of an element is determined by the number of electrons in its outer shell; it remains consistent within a group but varies across periods due to changes in electron configuration. - **Ionic Radii:** The size of ions follows the trends of atomic radii, but is influenced by the charge of the ion; cations are smaller than their parent atoms, while anions are larger. - **First Ionisation Energy:** The energy required to remove the first electron increases across a period due to greater nuclear attraction and decreases down a group due to increased electron shielding. - **Electronegativity:** This property increases across a period as atoms become more effective at attracting electrons and decreases down a group due to increased distance from the nucleus. ### Element Properties and Reactivity - **Metallic and Non-metallic Behaviors:** Metals, found in Groups 1 and 2, show increased reactivity down the group, while non-metals in Group 17 show decreased reactivity down the group. - **Oxides Across a Period:** The nature of oxides changes from basic on the left side of the periodic table to acidic on the right, with amphoteric oxides in the middle. ## 2. Properties of atoms ### 2.1 Periodic Table and Trends Elements are represented by symbols, and the periodic table is structured based on atomic number and properties of elements. Trends across periods and down groups include atomic radii, valencies, ionic radii, first ionization energy, and electronegativities, particularly in groups 1, 2, 13-18, and period 3. Successive ionization energy data correlates with electron configuration, indicating how tightly electrons are held by the nucleus. Metallic and non-metallic behaviors vary across groups, with alkali metals (Li-Cs) showing increasing reactivity down the group, while halogens (F-I) show decreasing reactivity down the group. Oxides transition from basic to amphoteric to acidic across a period, reflecting changes in element properties. Data analysis is crucial for explaining periodic trends, patterns, and relationships. ### 2.2 Atomic Structure Atoms consist of a nucleus surrounded by electrons in distinct energy levels, held by electrostatic forces; electron configurations represent electron locations. Nuclear symbol notation helps determine the number of protons, neutrons, and electrons in atoms, ions, and isotopes. The relative energies of s, p, and d orbitals are essential for constructing electron configurations for elements up to Z = 36, with the periodic table divided into four blocks: s, p, d, and f. The Aufbau principle, Hund's rule, and Pauli exclusion principle guide the writing of electron configurations and orbital diagrams. Chromium (Cr) and Copper (Cu) have unique electron configurations that deviate from expected patterns due to stability considerations. ### 2.3 Introduction to Bonding The ability of atoms to form chemical bonds is determined by their electron arrangement and the stability of their valence shell. The number of electrons lost, gained, or shared is dictated by the atom's electron configuration; transition metals can form multiple ions. Ions are charged atoms or groups of atoms, represented by formulas indicating the number of atoms and the ion's charge. Chemical bonds arise from electrostatic attractions due to electron sharing or transfer; valency indicates the number of bonds an atom can form. The formula of an ionic compound can be derived from the charges of the constituent ions, and naming conventions follow systematic rules. ### 2.4 Isotopes Isotopes are variants of the same element with different neutron counts, represented in IUPAC notation or as X-A. Isotopes share the same electron configuration and chemical properties but differ in physical properties. Relative atomic mass is defined as the weighted average mass of an element's isotopes compared to 1/12 the mass of a carbon-12 atom. ### Successive Ionization Energies Large increases in ionisation energy indicate the removal of electrons from a new, lower energy level, providing insight into the electron configuration of the element. ### Atomic Structure and Electron Configuration - **Atom Model and Structure:** Atoms consist of a nucleus containing protons and neutrons, surrounded by electrons in defined energy levels, held together by electrostatic forces. - **Electron configurations:** describe the distribution of electrons among the various orbitals, which is fundamental to understanding the periodic table's structure. ### Orbital energy and Electron Configuration Principles - **Aufbau Principle:** Electrons fill the lowest energy orbitals first before moving to higher levels, establishing a systematic approach to electron configuration. - **Hund's Rule:** When electrons occupy degenerate orbitals, they will fill each orbital singly before pairing up, maximizing the number of unpaired electrons. - **Pauli Exclusion Principle:** No two electrons in the same orbital can have the same spin, ensuring that each electron in an orbital has a unique set of quantum numbers. Exceptions to these rules, such as in the cases of Chromium (Cr) and Copper (Cu), occur due to the stability provided by half-filled or fully-filled d-orbitals. ### Bonding and Molecular Structure - **Formation of Chemical Bonds:** Atoms bond to achieve a stable electron configuration, often following the octet rule, which states that atoms tend to prefer having eight electrons in their valence shell. - **Ionic Bonds:** Formed through the transfer of electrons from one atom to another, resulting in the formation of charged ions that attract each other. - **Covalent bonds:** Involve the sharing of electrons between atoms, leading to the formation of molecules. ### Lewis Structures and Ionic Compounds - **Lewis Structures:** Diagrams that represent the valence electrons of atoms, showing both bonding pairs and lone pairs, which help predict molecular shapes and bond formation. - **Ionic Compounds:** Formed by balancing the charges of ions; for example, sodium chloride (NaCl) and calcium fluoride (CaF2) are common ionic compounds, with their formulas derived from the charges of the constituent ions. ### Isotopes and Analytical Techniques - **Isotopes and Their Properties:** Definition: Isotopes are variants of the same element that have the same number of protons but different numbers of neutrons, leading to different atomic masses. - **Chemical Properties:** Isotopes exhibit identical chemical properties due to their identical electron configurations, but they differ in physical properties such as mass and density. ### Relative Atomic Mass and Calculations - **Relative Atomic Mass:** Calculated as the weighted average of the isotopic masses of an element relative to the mass of carbon-12 (12C). - **Understanding how to calculate relative atomic mass** involves using the percentage abundances of isotopes, which can be determined through experimental techniques. ### Analytical Techniques in Chemistry - **Mass Spectrometry:** A technique used to identify isotopes and determine relative atomic masses by ionizing elements and separating ions based on their mass-to-charge ratio. - **Flame Tests and Atomic Absorption Spectroscopy (AAS):** These methods utilize electron transitions to identify elements and measure their concentrations in a sample. ### Emission and Absorption Spectra - **Emission Spectra:** are produced when excited electrons fall to lower energy levels, emitting light, while absorption spectra measure the wavelengths absorbed by electrons transitioning to higher energy levels.