Atomic Structure

What is an Atom? An atom is a unit of matter, The smallest unit of an element, Having all the characteristics of that element and Consisting of a dense, central, positively charged nucleus surrounded by a system of electrons.

There are the 3 major parts of an atom. Proton Neutron Electron

The structure of the atom The Ancient Greeks used to believe that everything was made up of very small particles. I did some experiments in 1808 that proved this and called these particles ATOMS: Dalton ELECTRON – negative, mass nearly nothing PROTON – positive, same mass as neutron (“1”) NEUTRON – neutral, same mass as proton (“1”)

The Atom Electron Nucleus Shell or Orbit

The Atom Hydrogen Proton Electron Hydrogen has one proton, one electron and NO neutrons

The Atom Helium Proton Electron Neutron Helium has two electrons, two protons and two neutrons

Mass and atomic number 4 He 2 Particle Relative Mass Relative Charge Proton 1 Neutron Electron -1 MASS NUMBER = number of protons + number of neutrons He 2 4 SYMBOL PROTON NUMBER = number of protons (obviously)

Nucleus The nucleus is the central part of an atom. It is composed of protons and neutrons. The nucleus contains most of an atom's mass. It was discovered by Ernest Rutherford in 1911.

Neutron Neutrons are uncharged particles found in the atomic nucleus. Neutrons were discovered by James Chadwick in 1932. Experiments done in the late 1960's and early 1970's showed that neutrons are made from other particles called quarks. Neutrons are made from one 'up' quark and two 'down' quarks.

Electron Electrons are negatively charged particles that surround the atom's nucleus. Electrons were discovered by J. J. Thomson in 1897. Electrons determine properties of the atom. Chemical reactions involve sharing or exchanging electrons.

Proton Protons are positively charged particles found in the atomic nucleus. Protons were discovered by Ernest Rutherford.. Experiments done in the late 1960's and early 1970's showed that protons are made from other particles called quarks. Protons are made from two 'up' quarks and one 'down' quark.

The Models of Atomic Structure

Dalton’s Atomic Model (experiment based!) All elements are composed of tiny indivisible particles called atoms Atoms of the same element are identical. Atoms of any one element are different from those of any other element. John Dalton (1766 – 1844)

Dalton’s Atomic Model (experiment based!) Atoms of different elements combine in simple whole-number ratios to form chemical compounds In chemical reactions, atoms are combined, separated, or rearranged – but never changed into atoms of another element.

Thomson’s Atomic Model J. J. Thomson Thomson believed that the electrons were like plums embedded in a positively charged “pudding,” thus it was called the “plum pudding” model.

Bohr’s Atomic Model In order to overcome the limitations of Rutherford’s atomic model Niles Bohr in 1913 modified the Rutherford model. The Bohr’s atomic model is based on certain basic postulates as stated below: Postulate concerning energy level Postulate concerning angular momentum Postulate concerning radiation of energy

The Rutherford Atomic Model The nucleus is composed of protons and neutrons (they make the nucleus!). The electrons distributed around the nucleus, and occupy most of the volume. His model was called a “nuclear model”.

The Rutherford Atomic Model Based on his experimental evidence: The atom is mostly empty space. All the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a “nucleus”.

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