ATOMIC STRUCTURE

• Leucippus and Democritus believed that all matter in nature consisted of atoms and the void

  (emptiness) around them.
• Democritus, atoms are small, tiny particles that are indestructible and completely full,
• Democritus named this very small piece of matter atomos, a Greek word that means indivisible

  particle.
• Aristotle, also a Greek philosopher, strongly contradicted Democritus' idea about

  atoms, believing that matter can be divided infinitely, with each piece getting smaller and smaller.
• John Dalton

  (1766-1844), an English physicist, came along and provided the first

  concrete evidence that atoms exist.
• 1803, John Dalton proposed his theory of the

  atom, commonly known as Atomic Theory, a theory of the nature of matter,

  in which its development was based on the works of earlier scientists.
• All matter is made up of tiny, indivisible particles called atoms. (stated by Dalton)
• All atoms of the same element are identical; different elements

  have different types of atoms. (stated by Dalton)
• Atoms can neither be created nor destroyed; they just rearrange

  in a chemical reaction to form new compounds. (stated by Dalton)
• 'Compound elements' (i.e., compounds) are formed when atoms of different elements join in

  simple ratios to form 'compound atoms' (i.e., molecules) (stated by Dalton)
• The law of conservation of mass states that in an ordinary chemical reaction,

  the total mass of the reactants should be equal to the total mass of the products. (by Dalton atomic theory)
• The law of definite proportion, established by

  Joseph Proust, states that different samples of pure

  compound will contain the same elements in the same

  proportion.
• The law of multiple proportions states that the mass of one element that can combine with a

  fixed mass of another element can be expressed in a ratio of small whole numbers.
• Around 1897, a scientist named Joseph John Thomson (1856-

  1940), a british phycisist
• J.J Thompson discovered that atoms have negatively charged particles, called electrons.
• cathode rays

  consist of fundamental particles present in the atoms of all elements.
• plum pudding model. According to Thompson, an atom was a large, positive,

  solid sphere.
• In 1911, Ernest Rutherford (1871-1973) and his colleagues tested Thompson's theory using a

  very thin sheet of gold foil.
• They focused on a stream of alpha particles and discovered that most of the

  particles passed through, and few were deflected.
• alpha scattering experiment suggested that an atom was mostly empty space.
• Rutherford theorized the center of the atom, which

  he called the nucleus, to be positive because it was able to repel the positively charged alpha particles.
• nucleus (which means "little nut" in Latin),
• Some years later, Rutherford's team was able to identify the positively charged particle in the

  nucleus, which is called the particle proton. After that, James Chadwick discovered neutrons
• Rutherford's model had orbiting electrons moving around the massive

  nucleus of the atom. However, James Maxwell had already shown that a

  charged particle moving through an electromagnetic field would continuously

  radiate energy.
• Danish physicist, Neil's Bohr (1885-1962), saw a possible solution in the Quantum Theory

  proposed in 1900 by Max Planck.
• Neils's bohr said that energy could be emitted not in continuous waves but in discrete packages that he called

  quanta.
• Sommerfield's solution was to assume that electrons moved in elliptical rather than a circular motion.