Development of the Atomic Theory READ pp. 1 - 8..
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Transcript of Development of the Atomic Theory READ pp. 1 - 8..
Development of the Atomic Theory
READpp. 1 - 8.
ATOMIC MODELS• In ancient Greece Democritus
argued:
– Atoms were the smallest particles of matter.
– “Atom”: (from Greek atomos, meaning “not able to be divided”
Toga!Toga!
4th Century
B.C.
John Dalton’s model:
• Matter is made up of atoms
• Atoms cannot be divided into smaller pieces
• All atoms of an element are exactly alike
• Different elements are made of different atoms
**An atom was a hard sphere that was the same throughout
1803
FIRST ATOMIC THEORY:
William Crookes’ experiment • Cathode ray tube• Electrode = metal that
conducts electricity• Anode (+) Cathode (-)• Battery connected,
greenish glow appeared in tube
• Shadow of cross fell at other end of tube
• Proof that something was traveling in a straight line through the tube and was deflected by the cross
JJ Thomson Model
• Discovered electrons!!• Thomson thought the
electrons were evenly mixed throughout the atom
The CRT particles were negatively charged.These particles – electrons – are part of every kind of atom
1897
Ernest Rutherford• Rutherford discovered that atoms contain a
small, dense, positively charged center called the nucleus.
1911
Neils Bohr: Improvements on Rutherford’s model
• 1920 – protons were identified (Rutherford)
• 1932 - neutrons were discovered because of inconsistencies in the mass of atoms (Chadwick)
Electrons
+
Neutrons
Protons
1913 Electrons move around nucleus in
different energy levels. Valence electrons are in outermost
level. They give an atom its chemical properties/reactivity
Niels Bohr
Electrons
Nucleus
Electrons
Bohr suggested that electrons (which have a negative charge) moved around the nucleus at certain fixed distances.Defined energy levels where electrons will likely orbit the nucleus.
Current Atomic Theory• According to the
current atomic theory, electrons are most likely to be found in the electron cloud around the nucleus.
Bohr’s Model!!!!!!!!!!!!!!!
What is Matter?
• Matter is anything that has mass and takes up space.
• The basic building blocks of all matter are atoms.
• An atom is the smallest particle into which an element can be divided and still be the same substance.
Parts of the Atom• Proton: a positively (+) charged particle of the
nucleus.• Neutron: a neutral particle of the nucleus.• Electron: a negatively (-) charged particle of
the nucleus.
Electron (-)
Neutron (neutral) (no charge)
Proton (+)
Nucleus(98% of themass of atom)
Electron Cloud (levels/orbits)
• Atomic Mass Unit (amu): the SI unit for the masses of particles in atoms.• Atomic Number: the number of protons in the nucleus of an atom. (P+)• Mass Number: number of protons and neutrons in an atom. (P+ + No)• Atomic Mass: the weighted average of the masses of all the naturally occurring isotopes of an element.
Molecules• A particle made of two or more atoms bonded
together forms a molecule. • For example, two hydrogen atoms join with
one oxygen atom to form a water molecule.
Elements
• An element is the simplest form of matter that cannot be changed into another simpler form by ordinary means.
• Examples of elements: Oxygen, Helium, Gold, Silver….
Compounds• A substance made of two or more elements
chemically combined form a compound.• Example: NaCl, H2O, CO2