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Chapter 2 the structure of the atom (part 2)
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Chapter 2 the structure of the atom (part 2)


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  • 1. 2.2 Atomic Structure  • • • • • John Dalton (1808) proposed that:All elements are made of atoms Atoms neither created or destroyed Atoms of the same element are alike and differ from different element When atoms are combined, they do so in a simple ratio Chemical reactions will results in combination or separation of atoms
  • 2. 2.2 Atomic Structure  • • J.J Thompson (1897) :Discovered negatively charged particles called electrons. Suggested that atom is positively charged sphere with electrons embeded inside it
  • 3. 2.2 Atomic Structure  • • • • Ernest Rutherford (1911) :Suggested that most of the atom must be empty space Proposed that all the positive charge is concentrated in nucleus. Named the positively charged particles as protons Proposed that an atom is a positively charged nucleus with a cloud of electrons surrounding it.
  • 4. 2.2 Atomic Structure  •  • • • Neils Bohr (1913) proposed that:Electrons in the atom are arranged in permitted orbits called electron shells surrounding the nucleus James Chadwick (1932) :Discovered neutrons; neutral subatomic particles. Neutron has mass almost the same as proton. Suggested that nucleus of atom contain proton and neutrons.
  • 5. 2.2 Atomic Structure  • • • • Proton Number :Number of proton in atom of an element Also known as atomic number Proton number also tell us the number of electrons. Eg:- Magnesium atom has 12 protons, thus it has 12 electrons.
  • 6. 2.2 Atomic Structure  • • • Nucleon Number :The sum of protons and neutrons in its atom Also known as relative mass Eg:- A sodium atom has 11 protons and 12 neutrons. Hence the nucleon number or relative mass is 23.
  • 7. 2.2 Atomic Structure  • • • • Symbols of element :Each element is represented with a symbol It may represented by the first letter of its name. Eg:- Hydrogen  H, Nitrogen  N Some is represented with a second letter added after its initial to differentiate between other elements. Eg:- Nickel  Ni Some are represented by its Latin name. Eg:Silver = Argentum  Ag.
  • 8. 2.3 Isotopes and their importance  • • • • Isotopes :Atoms of the same element with the same proton number but different nucleon numbers or same elements with same number of protons but different number of neutrons Have same chemical properties but different physical properties such as density and melting point Eg:- Cl-35, Cl-37. Unstable isotopes are radioactive isotopes which will undergo spontaneous decay to emit radioacctive rays. Eg:- Cobalt-60
  • 9. 2.4 The Electronic Structure of an Atom  • • • • • Electron arrangement in atom :Quantum orbit@ electron orbits. First shell are filled first with max of 2 electrons The remaining electrons are filled in the next shell with max of 8 electrons The remaining electrons then are filled into the third shell and can take a max of 8 to 18 electrons The way the electrons are distributed are called electron arrangement