The Atom
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Transcript of The Atom
THE ATOMSmallest particle of an element
that retains the properties of the element
THE BEGINNING Democritus first
suggested the existence of atoms in the 4th century BC.
John Dalton was the first to perform scientific experiments to test and correct his idea of the atom. He created the first
“Atomic Theory”
DALTON’S ATOMIC THEORY1. All elements are composed of tiny
indivisible particles called atoms.2. Atoms of the same element are
identical.3. Atoms of different elements can
combine physically or chemically (in whole number ratios to form compounds).
4. Chemical reactions occur when atoms are separated, joined, or rearranged.
However, not all holds true today…
THE ATOM DIVERSIFIES… Electrons – negatively charged
subatomic particlesDiscovered by J.J. Thomson in 1897
Conducted Cathode Ray Experiment
ELECTRON continuedRobert Millikan measured the quantity of
charge and the ratio of charge to mass of the electron Calculated the electron’s mass Oil Drop Experiment
THINGS WE KNOW ABOUT CHARGES Atoms have no net electric charge Electric charges are carried by particles
of matter Electric charges always exist in whole
number ratios When a given number of negatives
combines with the same number of positives, a neutral atom is formed.
So…we know there must be something POSITIVE inside the atom.
PROTONS Goldstein (1886) used cathode ray
tubeobserved a ray in the opposite direction
(canal rays)named particle the proton
Its mass was ~ 1840 times the mass of the electron
NEUTRONS Chadwick (1932) confirmed the
existence of the neutron Approx. same mass as the proton
STRUCTURE OF THE ATOM Thomson’s
“Plum Pudding” modelElectrons are
interspersed throughout positive material
PLUM PUDDING UNDER ATTACK Rutherford
tested Thomson’s theory
Gold Foil Experiment
GOLD FOIL EXPERIMENT
GOLD FOIL EXPERIMENT EXPLAINED Beam of Alpha particles directed at
gold foil. Particles were scattered suggesting a
dense mass of positive charge Rutherford proposed the idea of the
atomic nucleus.Most of the atom is empty spaceNucleus contains protons and neutronsSpace contains electrons
WHERE DOES THAT LEAVE US? In the atom, we have:
Protons (p+)Neutrons ( n0)Electrons (e-)
Protons and Neutrons are in the nucleus. Electrons are outside the nucleus.
Identities of elements are determined by the number of protons in the nucleus.
THE ATOM BY THE NUMBERS Atomic Number – number of protons
(whole number) Mass Number – Protons plus Neutrons
(number of particles in the nucleus) Atomic Mass – weighted average of
the masses of all isotopes of the element (decimal number) 6
C12.011
SAME ELEMENT…DIFFERENT NUMBERS Isotope – atoms of the same element
with different numbers of neutronsAtomic Number will be the SAMEMass Number will be DIFFERENTAtomic Mass will be the SAME
In an Isotope,Protons – SAMENeutrons - DIFFERENTElectrons – SAME
Ex. Carbon – 12 and Carbon - 14
PROTONS, NEUTRONS, ELECTRONS AND THE ATOM
Element Atomic
Number
Mass Numb
er
Protons
Neutrons
Electrons
9 10
14 7
21 20
13 27
56 26
Carbon-13
Beryllium-10
Neon-20
Boron-11
Sulfur-33
PROTONS, NEUTRONS, ELECTRONS AND THE ATOM
Element Atomic
Number
Mass Numb
er
Protons
Neutrons
Electrons
Fluorine-19 9 19 9 10 9
Nitrogen-14
7 14 7 7 7
Calcium-41 20 41 20 21 20
Aluminum-27
13 27 13 14 13
Iron-56 26 56 26 30 26
Carbon-13 6 13 6 7 6
Beryllium-10
4 10 4 6 4
Neon-20 10 20 10 10 10
Boron-11 5 11 5 6 5
Sulfur-33 16 33 16 17 16
ATOMS VS. IONS Atoms can also gain and lose electrons. An atom that has lost or gained an
electron is an ION. Positive Ions (CATIONS) form when
atoms lose electronsEx. Calcium-41 atom 20 p+ 20 e- 21 n0
Calcium-41 +2 ION 20 p+ 18 e- 21 n0
Negative Ions (ANIONS) form when atoms gain electrons. Ex. Oxygen-16 atom 8 p+ 8 e- 8 n0
Oxygen-16 -2 ION 8 p+ 10 e- 8 n0
IONS In an ION,
Protons – SameNeutrons – SameElectrons – Different
More electrons means a NEGATIVE ion.Anion (O2-)
Less electrons means a POSITIVE ion.Cation (Ca2+)