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Atoms and Elements
The Periodic Table
The periodic table is a systematic arrangement of all known chemical elements, organized by increasing atomic number and grouped according to similar chemical properties. This organization allows chemists to predict element behavior and relationships.
Groups: Vertical columns in the periodic table, containing elements with similar properties.
Periods: Horizontal rows, numbered from 1 to 7, representing elements with the same number of electron shells.
The periodic table was first created by Dmitri Mendeleev in 1869, who arranged elements by increasing atomic mass and grouped them by similar properties.
Groups and Periods
Elements are arranged in the periodic table according to their properties, forming vertical columns called groups and horizontal rows called periods.
Groups: Elements in the same group have similar chemical and physical properties.
Periods: Elements in the same period have the same number of electron shells but differ in properties.
Period 1: Contains 2 elements (H, He).
Period 2 and 3: Each contains 8 elements (e.g., Period 2: Li, Be, B, C, N, O, F, Ne).
Group Numbers and Naming
Group numbers identify the vertical columns of the periodic table and can be written in two ways:
The letter A is used for representative elements (Groups 1A–8A).
The letter B is used for transition elements (Groups 3B–12B).
Alternatively, groups are numbered 1–18 from left to right.
Certain groups have common names:
Group 1A (1): Alkali metals (Li, Na, K, Rb, Cs, Fr)
Group 2A (2): Alkaline earth metals (Be, Mg, Ca, Sr, Ba, Ra)
Group 7A (17): Halogens (F, Cl, Br, I, At, Ts)
Group 8A (18): Noble gases (He, Ne, Ar, Kr, Xe, Rn, Og)
Classification of Elements: Metals, Nonmetals, and Metalloids
The periodic table is divided into three broad categories based on physical and chemical properties:
Metals: Located to the left of the zigzag line. Shiny, ductile, malleable, good conductors of heat and electricity, and usually solid at room temperature (except mercury).
Nonmetals: Located to the right of the zigzag line. Dull, brittle, poor conductors, and often gases or solids with low melting points.
Metalloids: Found along the zigzag line. Exhibit properties intermediate between metals and nonmetals; often semiconductors.
Comparison Table: Properties of Metals, Nonmetals, and Metalloids
Property | Metal (e.g., Antimony) | Metalloid (e.g., Silicon) | Nonmetal (e.g., Sulfur) |
|---|---|---|---|
Appearance | Silvery-gray, shiny | Shiny or dull | Dull, yellow |
Malleability | Can be hammered into sheets | Brittle | Shatters when hammered |
Conductivity | Good conductor of heat and electricity | Moderate conductor (semiconductor) | Poor conductor |
Density | High (e.g., 10.5 g/mL) | Intermediate (e.g., 6.7 g/mL) | Low (e.g., 2.1 g/mL) |
Uses | Coins, jewelry, wires | Electronics, glass, plastics | Gunpowder, fungicides |
Essential Elements for Health
About 20 elements are essential for human health. Four elements—oxygen, carbon, hydrogen, and nitrogen—make up 96% of body mass. Other elements, called macrominerals and microminerals (trace elements), are required in smaller amounts for various physiological functions.
Macrominerals and Their Functions
Element | Approximate Quantity in 60 kg Person | Function |
|---|---|---|
Calcium (Ca) | 1000 g | Bone and teeth formation, muscle contraction, nerve impulses |
Phosphorus (P) | 600 g | Bones, teeth, nucleic acids |
Potassium (K) | 120 g | Most common positive ion inside cells, muscle contraction, nerve impulses |
Chlorine (Cl) | 100 g | Most common negative ion outside cells, stomach acid (HCl) |
Sulfur (S) | Varies | Component of proteins, liver, vitamins, insulin |
Sodium (Na) | Varies | Most common positive ion outside cells, water balance, muscle contraction, nerve impulses |
Magnesium (Mg) | Varies | Component of bones, required for metabolic reactions |
Microminerals (Trace Elements) and Their Functions
Element | Function |
|---|---|
Iron (Fe) | Component of hemoglobin for oxygen transport |
Copper (Cu) | Growth, maintenance of bones, tendons, hair, skin |
Zinc (Zn) | Metabolic reactions, DNA synthesis, immune system |
Selenium (Se) | Immune system, heart and pancreas health |
Iodine (I) | Thyroid function |
Manganese (Mn) | Bone growth, blood clotting, metabolism |
Molybdenum (Mo) | Processing iron and nitrogen from food |
Chromium (Cr) | Blood sugar maintenance, biomolecule synthesis |
Cobalt (Co) | Component of vitamin B12, red blood cell formation |
Fluorine (F) | Bone and teeth formation, energy from food |
Arsenic (As) | Growth and reproduction (in trace amounts) |
Additional info: The periodic table is a foundational tool in chemistry, essential for understanding element classification, predicting chemical behavior, and recognizing the biological importance of elements in health and disease.
