1. Atomic Structure

2. The History Of The Atom

3. Democritus (460 – 370 BC)
Atomism and Atoms

4. Democritus Lived in the fourth century B.C. Greece
(400 BC – 301 BC)
He had the thought that :
- matter was composed of tiny indivisible particles called atoms.

5. 4th century BC Greece
Parthenon built 447 BC– 432 BC

6. Photo Credit: timerime.com
Atoms are invisible, indestructible, fundamental units of matter
Ideas not entirely useful because it lacked experimental support.

7. John Dalton
Photo credit: US Library of Congress
Dalton was an English Chemist, Physicist, and meteorologist

8. An atom is an indivisible sphere with a uniform density throughout.
Dalton’s Atomic Model
An atom is an indivisible sphere with a uniform density throughout.
1807

9. All elements are composed of submicroscopic, indivisible particles called atoms
Atoms of the same element are identical. The atoms are different from those of other elements.

10. Atoms of different elements can physically mix together or can chemically combine with one another in simple whole-number ratios to form compounds.
Chemical reactions occur when atoms are separated, joined, or rearranged.
Atoms of one element are never changed into the atoms of another element as a result of chemical reactions.

11. What was going on in 1807
President:
Thomas Jefferson

13. Electrons

14. Sir J.J. Thompson
Discovered electrons , negatively charged particles, in 1897.
Performed the cathode ray experiment to conclude that there are negatively charged particles that are part of the atoms of all elements.

15. In 1909, Robert Millikan measured the charge of the electron
Oil drop experiment

16. E. Goldstein
Concluded that atoms have positively charged particles called protons.
This was done through a similar cathode ray experiment

17. Sir James Chadwick
Confirmed the existence of the neutron

18. Rutherford

19. Ernest Rutherford Known for the Gold foil experiment
He directed a narrow beam of alpha particles at a very thin piece of gold foil. They expected the beam to pass right through.
The particles deflected

20. A few particle bounced straight back to the source.
Based on this experiment , he concluded that there was something in the center of the atom that contained mass.
This small region is known as the nucleus.

23. Rutherford’s Model
electrons
protons

25. Niels Bohr

26. Niels Bohr
Bohr’s theory gets you away from the original thought that all orbital are in one big circle circle
His theory says that electrons are arranged in concentric circular paths, or orbits.

27. BOHR’S MODEL - +

28. Atomic Number
and
Isotopes

29. Atoms are made up of:
Protons
Electrons
Neutrons

30. Protons Positive charge Located in nucleus Mass of 1 amu
Number is always equal to the atomic number of its element

31. Electrons Negative charge Located outside the nucleus
Mass close to zero amu
Number is equal to number of protons in a neutral atom

32. Neutrons No charge – neutral Located in nucleus Mass of 1 amu
Number is equal to
mass number – atomic number

33. The Atomic Number of an element is:
The number of protons in the
nucleus of one of its atoms.
This number also equals the
number of electrons in the
neutral atom.

34. Mass Number
The mass number is the total
number of protons and neutrons
in the nucleus.
Mass Number = p + n

35. New Notation
Mass number Chemical
atomic number Symbol

36. 6 Li 34 Cl 3 17 Au
184
158 U 92 79

37. Atoms of the same element that contain different numbers of
Isotopes
Atoms of the same element that
contain different numbers of
neutrons and have different
atomic masses.
(The number of protons remains the same.)

38. All atoms have isotopes.
Isotopes do not exhibit chemical
behavior different from the
neutral atom.
Some atoms have isotopes that occur in nature, others have isotopes that are artificially created.
Because the electrons govern the chemical behavior of an atom, they also govern the chemical behavior of the isotope.

39. Isotopes 6 Li
Lithium-6 3 7 Li
Lithium-7 3

40. Isotopes and atomic mass
The atomic mass is the average
atomic mass of all the isotopes
of an element.

41. Isotopes and Radioactivity
Unstable isotopes emit radiation
as they decay. Isotopes decay
because they want to become stable.
The majority of isotopes are
unstable.