Atomic Theory: From Ancient Greece to Modern Chemistry
The Atom: From Ancient Greece to Modern Chemistry
The Atom in Ancient Greece
Ancient Greek philosophers debated the nature of matter. Some of their most relevant ideas were:
Leucippus and Democritus
In the 5th century BC, Leucippus proposed that matter was composed of a single type, and dividing it into smaller and smaller parts would eventually result in an indivisible piece. Democritus called these pieces “atoms,” meaning “no division.” Their atomistic philosophy can be summarized as follows:
- Atoms
Genomic DNA Isolation from Cheek Epithelium: A Step-by-Step Guide
Genomic DNA Isolation from Cheek Epithelium
Exercise 1: Isolation of Genomic DNA from Cheek Epithelium Cells
Isolation and purification of nucleic acids is the first phase of the majority of procedures applied in molecular biology. Obtaining pure genetic material, regardless of its origin, is the basic aim of such work. Many methods exist for nucleic acid isolation and purification. Choosing the most suitable method depends on several factors:
- The type of nucleic acid being analyzed (RNA/DNA)
- The organism
Dalton’s Atomic Theory and the Periodic Table of Elements
Dalton’s Atomic Theory
Accepted for much of the 19th century, Dalton’s Atomic Theory proposed the following:
- All matter is made up of tiny, invisible particles called atoms.
- Atoms are indivisible (from the Greek word ‘atomos’, meaning uncuttable) and permanently unalterable.
- There are many kinds of atoms, but atoms of the same element have the same mass and properties.
- Atoms of one element are different from atoms of other elements.
- Atoms take part in chemical combinations, leading to the Law of Definite
Dalton’s Atomic Theory and the Periodic Table of Elements
Dalton’s Atomic Theory
Accepted for much of the 19th century, Dalton’s Atomic Theory proposed the following:
- All matter is made up of tiny, invisible particles called atoms.
- Atoms are indivisible (atomos, Gr.), permanently unalterable.
- There are many kinds of atoms, but atoms of the same element have the same mass and properties.
- Atoms take part in chemical combinations.
This theory led to the development of the Law of Definite Composition (LDC) and the Law of Multiple Proportions (LMP).
LDC – Law of Definite
Read MoreAlkene & Alkyne Addition Reactions: Key Terms & Concepts (Ch 8)
Chapter 8: Alkenes & Alkynes II: Addition Reactions
Key Terms and Concepts
Electrophile
An “electron-loving” species; a cation or electron deficient molecule (with a δ+ charge, or an empty p orbital) that can accept a pair of electrons to form a new covalent bond. Examples include:
- Brønsted-Lowry acids (proton donors) such as HBr, H2SO4, etc.
- Lewis acids (electron-pair acceptors) such as BH3, BF3, AlCl3, FeCl3, ZnCl2, etc.
- Metal ions with vacant orbitals such as Ag+, Hg2+, Pt2+, etc.
- Neutral molecules
Evolution of Atomic Theory: From Democritus to Chadwick
Democritus
Ideas:
All matter is made up of water, air, fire, and earth.
Matter is composed of atoms, which move through empty space. They are solid, homogeneous, indestructible, and indivisible. There are different kinds of atoms, having different sizes and shapes. Matter can be divided, but at some point, it can’t be divided any further, and its name is atom.
Dalton
Background:
Making experiments with gases, law of conservation of mass defined, and multiple proportions.
Ideas:
- Matter is composed of extremely