The Periodic Table
Section: 8. The Periodic Table | Syllabus: Cambridge AS Level Physics 9702
The Modern Periodic Table The Periodic Table is a systematic arrangement of all known chemical elements organized by their atomic structure and properties. Elements are positioned based on their atomic number (number of protons), which increases from left to right and top to bottom.
Periodic Table An arrangement of elements in order of increasing atomic number, displaying repeating patterns in chemical and physical properties. Historical Development The modern Periodic Table was developed by Dmitri Mendeleev in 1869, who arranged elements by atomic mass and left gaps for undiscovered elements.
Mendeleev arranged elements in order of increasing atomic mass He placed elements with similar properties in vertical columns He left gaps for elements not yet discovered He predicted properties of missing elements Modern table arranges elements by atomic number, not mass Why Atomic Number?
The modern Periodic Table uses atomic number (number of protons) rather than atomic mass because it more accurately reflects chemical behavior and electron configuration. Diagram The modern Periodic Table showing all 118 elements arranged in periods (1-7) and groups (1-18), with atomic numbers labeled Periods and Groups The Periodic Table is organized into horizontal rows called periods and vertical columns called groups .
This arrangement reveals fundamental patterns in element structure and behavior. Feature Periods Groups Orientation Horizontal rows Vertical columns Numbering 1 to 7 1 to 18 (or I to VIII) Significance Period number = number of electron shells Group number = number of outer shell electrons Properties Properties change across a period Elements in same group have similar chemical properties Understanding Periods Period 1 : Only 2 elements (H, He) - 1 electron shell Period 2 : 8 elements (Li to Ne) - 2 electron shells Period 3 : 8 elements (Na to Ar) - 3 electron shells Period 4-7 : Contain transition metals and have more elements As you move across a period, atomic number increases by 1 Understanding Groups Elements in the same group have the same number of outer shell electrons This gives them similar chemical properties Group 1: 1 outer electron, Group 2: 2 outer electrons Group 17: 7 outer electrons, Group 18: 8 outer electrons (except He) Elements in same group show trends in reactivity and physical properties Electron Configuration Link The period number tells you how many electron shells an atom has.
The group number (for main group elements) tells you how many electrons are in the outer shell. Diagram Periodic Table with periods highlighted horizontally (1-7) and groups highlighted vertically (1-18), showing example elements with their electron shell configurations Metals, Non-metals, and Metalloids The Periodic Table is divided into three main categories of elements based on their physical and chemical properties.
A zigzag line (staircase) separates metals from non-metals, with metalloids positioned along this boundary. Metals Metals occupy the left side and center of the Periodic Table, making up about 75% of all elements.
Good conductors of heat and electricity Lustrous (shiny) when polished Malleable - can be hammered into thin sheets Ductile - can be drawn into wires High density and high melting points (generally) Solid at room temperature (except mercury - Hg) Form positive ions (cations) by losing electrons React with oxygen to form basic oxides Examples: Sodium (Na), Magnesium (Mg), Aluminium (Al), Iron (Fe), Copper (Cu), Gold (Au) Non-metals Non-metals are located on the right side of the Periodic Table.
Poor conductors of heat and electricity (insulators) Dull appearance (not lustrous) Brittle when solid - shatter rather than bend Lower density and lower melting points than metals Can exist as gases, liquids, or solids at room temperature Form negative ions (anions) by gaining electrons React with oxygen to form acidic oxides Examples: Hydrogen (H), Carbon (C), Nitrogen (N), Oxygen (O), Sulfur (S), Chlorine (Cl) Metalloids (Semi-metals) Metalloids are elements that have properties intermediate between metals and non-metals.
Found along the zigzag line separating metals and non-metals Can conduct electricity but not as well as metals ( semiconductors ) Used in electronic devices and computer chips Have physical properties of both metals and non-metals Examples: Boron (B), Silicon (Si), Germanium (Ge), Arsenic (As) Silicon in Technology Silicon (Si) is a metalloid and the most important semiconductor material.
It's used in computer chips, solar panels, and electronic devices due to its intermediate conductivity. Diagram Periodic Table color-coded showing metals (blue/grey on left), non-metals (yellow/green on right), and metalloids (orange) along the zigzag staircase line Important Groups Certain groups in the Periodic Table have special names and distinctive properties that make them particularly important.
Elements within these groups share similar chemical behavior due to having the same numbe…
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