the atom. the building block of matter 400 bc democritus (greek philosopher) atomos =...
TRANSCRIPT
The Atom
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
1808 John Dalton (English Chemist) Using experiments formulates the first
atomic theory1. All elements are composed of indivisible
particles called atoms2. Atoms of the same elements are exactly the
same3. Atoms of different elements are different4. Two or more elements combine to form
compounds
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
1897 Discovers the electron
Ernest Rutherford (English Physicist)
Gold Foil Experiments1908 Discovers that the
atom is mostly empty space
Discovers a hard, dense center of the atom called the NUCLEUS
The Gold Foil Experiment
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
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
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
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 Subatomic Particles
Particle Location Mass (AMU)
Charge
Electron Electron Cloud
0 negative
Proton Nucleus 1 positive
Neutron Nucleus 1 neutral
Finding the Number of Subatomic
Particles in an Atom
Atomic Number = the number of protons in the nucleus of an atom
Identifies each elementHydrogen 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)
Electrons
IF the 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
Sodium will lose one electron when it bondsNa+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
Chlorine will gain an electron when it bondsCl-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
The two subatomic particles that have mass?Proton and neutron, both found in the nucleusMass Number = # of Protons + # of Neutrons
Mass # - Atomic # = # of neutrons
Practice Problems
Symbol Atomic Number
Mass Number
Charge Protons Neutrons Electrons
Mg 12 24 0 12 12 12
K 19 39 0 19 20 19
Na+1 11 23 +1 11 12 10
F-1 9 19 -1 9 10 10
Mg+2 12 24 +2 12 12 10
ISOTOPES
Atoms of the same element with a different number of neutrons.
Ex: carbon-12 & carbon-14 Carbon-12
1. 6 protons2. 6 neutrons3. 6 electrons
Carbon-141. 6 protons2. 8 neutrons3. 6 electrons
Isotopes of Hydrogen
Hydrogen-1 (protium) 0 neutronsHydrogen-2 (deuterium) 1 neutronHydrogen-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-levelsSub-levels are divided into orbitalsAll of these levels, sub-levels & orbitals can
overlap.
VALENCE ELECTRONS
Valence electrons = the outermost electrons
The electrons involved in bondingDetermines the chemical properties of an
atom
More about Electrons
Maximum # of electrons on each energy level
Level 1 = 2 electronsLevel 2 = 8 electronsLevel 3 = 18 electronsLevel 4 = 32 electrons
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.
1. gain electrons2. lose electrons3. share electrons
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.
Valence electrons determine how atoms will bond with other atoms in order to complete their outer-most energy level.
The Stable 8 CHEMICAL BONDING
Ionic bonding (gaining/losing of electrons) Covalent bonding (sharing of electrons)
Concepts Coming Up Next