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The Atom. What to look for: Three Essential Questions E. Q. #1 = What are the parts of an atom? E. Q. #2 = In what manner can subatomic particles be differentiated? E. Q. #3 = How does the atomic structure impact chemical change & reactivity?. The Building Block of Matter.

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the atom
The Atom

What to look for:

Three Essential Questions

E. Q. #1 = What are the parts of an atom?

E. Q. #2 = In what manner can subatomic particles be differentiated?

E. Q. #3 = How does the atomic structure impact chemical change & reactivity?

the building block of matter
The Building Block of Matter
  • 400 BC Democritus (Greek Philosopher)
  • Atomos = “indivisible”
  • …like a brick is used to build a building; an atom is used to build all matter…
first atomic theory
First Atomic Theory
  • 1808 John Dalton (English Chemist)
  • Using experiments formulates the first atomic theory
    • All elements are composed of indivisible particles called atoms
    • Atoms of the same elements are exactly the same
    • Atoms of different elements are different
    • Two or more elements combine to form compounds
subatomic particles
Subatomic Particles
  • The idea that the atoms was not a solid sphere, but a composition of small particles which came to be known as subatomic particles
  • Julius Plucker, William Crooks & J J Thomson
  • mid-1800’s
j j thomson
J J Thomson
  • 1897 Discovers the electron
ernest rutherford english physicist
Ernest Rutherford (English Physicist)
  • Gold Foil Experiments
  • 1908 Discovers that the atom is mostly empty space
  • Discovers a hard, dense center of the atom called the NUCLEUS
the atom is mostly empty space
The atom is mostly empty space
  • Most of the particles passed straight through to gold foil.
  • First important discovery by Rutherford
the nucleus is discovered
The NUCLEUS is Discovered
  • 1911 Rutherford proves that the particles that do not pass through are hitting a small, dense center of the atom called the nucleus.
  • Rutherford later goes on to discover the proton


Name three major discoveries made by Ernest Rutherford & the Gold Foil Experiment:

1. _______________________________________

2. _______________________________________

3. _______________________________________

What are the two results of firing particles at atoms in the foil of the Gold Foil Experiments:

1. _______________________________________

2. _______________________________________



Who was the first to attempt to form a complete atomic theory?

1. _______________________________________

electron energy levels
Electron Energy Levels
  • 1913 Niels Bohr (Danish physicist) discovers the electrons travel around the outside of the atom on different energy levels
  • The Bohr Model = “solar system” model
the neutron is found
The Neutron is Found
  • 1932 James Chadwick proves the existence of the neutron.
  • Only 4 years later the neutron is used to split the first atom
  • Why was the neutron’s existence more difficult to prove?
  • What evidence hinted of its existence? “the missing mass”

E. Q. #1 = What are the parts of an atom?

the subatomic particles
The Subatomic Particles

E. Q. #2 = In what manner can subatomic particles be differentiated?

finding the number of subatomic particles in an atom
Finding the Number of Subatomic Particles in an Atom
  • Atomic Number = the number of protons in the nucleus of an atom
  • Identifies each element
  • Hydrogen is 1 and it has 1 proton in its nucleus (only hydrogen has 1 proton)
  • Helium is 2 and it has 2 protons in its nucleus (only helium has 2 protons)
  • IFthe atom is neutral (same number positive charges as negative charges) then the number of electrons will be the same as protons.
  • ION = a charged atom (unequal number of protons and electrons)
  • +1 charge = the atom LOST one electron
  • -1 charge = the atom GAINED one electron
  • +2 charge = LOST 2 electrons
  • -2 charge = GAINED 2 electrons and so on
example of ions
Example of Ions
  • Sodium will lose one electron when it bonds
  • Na+1 or Na+
  • Sodium’s atomic number is 11, so it has 11 protons.
  • The +1 charge means Na+1 has 10 electrons
another example
Another Example
  • Chlorine will gain an electron when it bonds
  • Cl-1 or Cl-
  • Chlorine’s atomic number is 17, so it has 17 protons
  • The -1 charge means Cl-1 has 18 electrons
mass number
Mass Number
  • The two subatomic particles that have mass?
  • Proton and neutron, both found in the nucleus
  • Mass Number = # of Protons + # of Neutrons
  • Mass # - Atomic # = # of neutrons
practice problems
Practice Problems

Do Parts of the Atom & Atomic Structure practice sheet now.

  • Atoms of the same element with a different number of neutrons.
  • Ex: carbon-12 & carbon-14
  • Carbon-12
      • 6 protons
      • 6 neutrons
      • 6 electrons
  • Carbon-14
      • 6 protons
      • 8 neutrons
      • 6 electrons
isotopes of hydrogen
Isotopes of Hydrogen
  • Hydrogen-1 (protium) 0 neutrons
  • Hydrogen-2 (deuterium) 1 neutron
  • Hydrogen-3 (tritium) 2 neutrons
the electron cloud
  • The electron cloud is separated by different energy levels.
  • Electrons with less energy travel on the levels closest to the nucleus.
  • Energy levels are divided into sub-levels
  • Sub-levels are divided into orbitals
  • All of these levels, sub-levels & orbitals can overlap.
valence electrons
  • Valence electrons = the outermost electrons
  • The electrons involved in bonding
  • Determines the chemical properties of an atom

E. Q. #3 = How does the atomic structure impact chemical change & reactivity?

Do Practice sheets What Is This Atom Now? 1 & 2 now.

more about electrons
More about Electrons
  • Maximum # of electrons on each energy level
  • Level 1 = 2 electrons
  • Level 2 = 8 electrons
  • Level 3 = 18 electrons
  • Level 4 = 32 electrons
the stable 8
“the Stable 8”
  • Due to the overlapping levels, sub-levels and orbitals the maximum number of outer most electrons is EIGHT.
  • An atom is becomes stable when it outer-most energy levels is full of electrons
  • This explains the chemical bonding properties of the atoms
  • Atoms will do one of three things in order to fill their outer most energy levels.
      • gain electrons
      • lose electrons
      • share electrons
concepts coming up next
Concepts Coming Up Next
  • The number of valence electrons an atom has determines the group it becomes to on the PERIODIC TABLE.
  • Groups or families of elements on the periodic table has similar chemical properties.
concepts coming up next1
Concepts Coming Up Next
  • Valence electrons determine how atoms will bond with other atoms in order to complete their outer-most energy level.
  • The Stable 8
      • Ionic bonding (gaining/losing of electrons)
      • Covalent bonding (sharing of electrons)