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?