Atomic Structure and the Periodic Table

Key Discoveries in Atomic Theory

Thomson's Discovery of Electrons

J.J. Thomson demonstrated that atoms contain tiny, negatively charged particles called electrons. He showed that atoms could lose electrons, suggesting a static atomic model.

Rutherford's Atomic Model

Ernest Rutherford established that atoms are mostly empty space. He proposed that a small, dense region, which he named the nucleus, resides at the atom's center. This nucleus contains protons and, as Rutherford suspected, neutrons. In his model, the number of protons equals the number of electrons, with the latter orbiting the nucleus in circular paths.

The Atom as a Planetary System

The Rutherford model is analogous to a planetary system because the nucleus represents the sun, and the electrons orbiting it are like planets.

Atomic Number and Mass Number

• Mass Number: Number of protons + Number of neutrons
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• Atomic Number: Number of protons = Number of electrons
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Isotopes: Variations Within Elements

Isotopes are atoms of the same element that have different mass numbers due to varying numbers of neutrons.

Calculating Relative Atomic Mass

a) The relative atomic mass (Mr) is calculated as a weighted average based on the abundance of each isotope's mass within an element: Mr = M1% + M2%...

b) For example: Mr = 34.97 x 75.5% + 36.94 x (100 - 75.5)% = 35.45

Electrons in the Outermost Shell

1. Elements with 3 electrons in their outermost shell.
2. Sulfur (S) has 6 electrons.
3. Beryllium (Be) has 2 electrons.
4. Chlorine (Cl) has 7 electrons.
5. Sodium (Na) has 1 electron.

Radioactivity: Natural and Artificial

a) Natural Radioactivity: The spontaneous emission of radiation by unstable atomic nuclei, transforming them into more stable nuclei. Artificial Radioactivity: Occurs when stable isotopes are bombarded with various particles, inducing radioactivity.

b) Types of radioactive emissions include Gamma (γ), Beta (β), and Alpha (α).

Applications of Radioactivity

1. Development of new crop varieties that are high-yielding, adaptable, and disease-resistant.
2. Use of isotopes in biological and medical research.
3. Sterilization of food products.
4. Development of novel materials.

Molecules and Crystalline Networks

Molecules: Element molecules consist of two or more atoms of the same element. Compound molecules are made up of two or more atoms of different elements.

Crystalline Networks: These structures are composed of an indefinite number of particles, where the constituent elements are arranged in an orderly, geometric pattern.

Groups in the Periodic Table

• Alkali Metals: Lithium (Li), Sodium (Na), Potassium (K), Rubidium (Rb), Cesium (Cs), Francium (Fr)
• Alkaline Earth Metals: Beryllium (Be), Magnesium (Mg), Calcium (Ca), Strontium (Sr), Barium (Ba), Radium (Ra)
• Halogens: Fluorine (F), Chlorine (Cl), Bromine (Br), Iodine (I), Astatine (At)

Similar Chemical Properties

Elements within the same group of the periodic table exhibit similar chemical properties because they have the same number of electrons in their outermost, or valence, shell.