Atomic Theory & Atomic Structure
Atoms: The Building Blocks
of Matter
Atoms- the smallest particle of matter which will exhibit the properties of that element.
ATOMS = BUILDING BLOCKS
Na
Mg
H
How small is an atom?
• http://www.youtube.com/watch?v=aQnbF-zpDiM
The scale of things-
UniverseGalaxyPlanetary
SystemsPlanets
Biospheres
Ecosystems
Populations Organisms
Systems
Organs
Tissues
Cells
Cell Organelles
Macromolecules
Molecules
Elements
AtomsWow! All of that is possible because of atoms.
Biggest
Big
Small
Smallest
When atoms are broken down,
the parts (protons, electrons, and neutrons)
of different elements look the same!
That’s why we say that the atom is the smallest particle that retains it’s own unique properties.
Draw this…
Electron (e-)
Proton (p+)
Neutron (n0)
}nucleus
Mystery Box
• try to figure out what is inside the “Mystery Box” WITHOUT OPENING IT!!!!
Atomic Model of MatterIn order to develop the atomic theory of matter, scientists used indirect evidence without seeing or touching the object but relied on how matter
behaves.
This was WAY before technology actually allowed us to “SEE” an atom!
Historical Development of the Atom (Atomic Theory)
How did we discover atoms and all its parts?
HISTORICAL DEVELOPMENT
Democritus- 400 B.C.- atoms were first suggested by Democritus, an ancient Greek and student of Aristotle. Aristotle rejected this
theory and claimed that his theory of matter being
infinitely divisible and continuous in
nature were correct.
John Dalton (1808)
John Dalton (1808) - British chemist who was the first to have a
theory about matter being composed of atoms and how these atoms might look and behave.
- He conceived of the atom as a solid billiard ball.
Dalton’s Model of the AtomDRAW THIS IN YOUR NOTES!!
SOLID BALL OF MATTER (no protons, neutrons, or electrons!)
Dalton's Atomic Theory (Daton’s Postulates):
1.All elements are composed of atoms that are indivisible.
2.All atoms of the same element are identical.
3. Atoms of different elements are different (they have different numbers of protons, and they MAY also differ in mass numbers).
Dalton's Atomic Theory (Dalton’s Postulates):
4. Atoms of different elements can combine with each other in simple whole number ratios to form compounds.
5.Chemical reactions occur when atoms are separated, joined, or rearranged. However, atoms of one element ARE NOT changed into atoms
of another element by a chemical
reaction.
J. J. Thomson (1903)
J. J. Thomson
Thomson was a British chemist who discovered the electron with the cathode ray tube experiment!
He was the first to discover one of the subatomic particles in the atom!
Thomson’s Model of the Atom
• “Plum Pudding” or “Chocolate Chip Cookie Dough” Model.
• A ball of positive charge containing a number of electrons.
DRAW THIS IN YOUR NOTES!!
J. J. Thomson• Cathode Ray Tube Experiment:
– Thomson shot an electrical charge through a cathode ray tube. He saw that the particles deflected towards the positive end of the tube. This meant that atoms contained a negative charge!
http://www.youtube.com/watch?v=IdTxGJjA4Jw
http://www.youtube.com/watch?v=RW_zfKOU9uM
Ernest Rutherford (1911)
Ernest Rutherford- 1911
• discovered the nucleus with the gold foil experiment and realized that
• The main part of the atom’s mass is in the nucleus• The nucleus has a positive charge.• Atoms are mostly empty space except for the nucleus.
Rutherford’s Model of the atom
Postively-charged Nucleus
Empty Space
Negatively-charged Electrons
DRAW THIS IN YOUR NOTES!!
Ernest Rutherford• Gold Foil Experiment:
– Shot alpha particles (positively-charged particles) at a sheet of gold foil. Saw that most particles pass through the foil and some deflected straight back at different angles. This meant that the atom is MOSTLY EMPTY SPACE with a positively-charge nucleus.
http://www.youtube.com/watch?v=wzALbzTdnc8&NR=1
http://www.youtube.com/watch?v=5pZj0u_XMbc
Niels Bohr (1913)
Neils Bohr• was a student of
Rutherford and believed that the model needed some improvement. Bohr proposed that an electron is found only in specific circular paths, or energy levels, around the nucleus.
Niels Bohr
• In the Bohr model:
1) each electron has a fixed energy called an energy level.
2) The lower the level, the lower the energy, the closer to the nucleus.
3) An electron cannot exist between energy levels.
http://www.youtube.com/watch?v=wCCz20JOXXk
Bohr’s Model of the atom
Nucleus
Electrons(orbiting the
nucleus)
DRAW THIS IN YOUR NOTES!!
Neils Bohr• In the Bohr Model, to move
from one energy level to another, an electron must gain or lose the right amount of energy.– Quantum- the energy required
to move an electron from one energy level to another. The energy of an electron is said to be quantized.
Atomic Structure
What are the parts of the atom?
The Atom and subatomic particles-
Protons- positively charged particles inside the nucleus,
Protons DEFINE/IDENTIFY an atom!!!!
Neutrons-neutral particles inside the nucleus
Electrons-negatively-charged particles outside the nucleus
Practice:
Particle Mass (kg) Mass (amu)
Charge
p+ 1.67493 x 10 -27
n 1.67262 x 10 -27
e- 9.10939 x 10 -31
Parts of the Atom
1. Atomic Number (Z) - #p (number of protons)
2. Mass Number- #p + #n (everything in the nucleus). This is NOT on the P.T.!!!
• Most atoms are NEUTRAL. This means #p = #e.
• But sometimes, the # of protons DOES NOT equal the # of electrons…
3. Ion: A charged atom (#p = #e)
Cation:
- POSITIVELY(+) charged atom that LOSES an electron
Anion:
- NEGATIVELY (-) charged atom that GAINS an electron
Isotopes
4. Isotope- an atom of the same element that has a different number of NEUTRONS
Reading the Periodic Table
Element Name
Atomic Number (#protons)Element Symbol
Average atomic Mass (amu)
6
CCarbon12.011
Atomic Symbols
6C12 2-
Mass Number (#p + #n) Charge (#p - #e)
Atomic Number (#p)
Other Info
• Mass Number = #p + #n• NOT the same as Atomic Mass…
you CAN’T find this on the P.T.!
• About electrons: – If #e = #p --- NEUTRAL ATOM
– If #e = #p --- ION
Beans activity
• A Carbon atom has:– 6 protons– 6 neutrons– 8 electrons
• Create a “bean atom” of carbon.
• Is this atom NEUTRAL? Why or why not?
• What is the charge of this atom?
Beans activity• A different Carbon atom has:
– 6 protons– 7 neutrons– 8 electrons
• Create a “bean atom” of carbon.• What is different about this atom?• What is it called when two atoms of the same
element have different number of neutrons?