1. Atomic Theory & Periodic Trends

2. Where Did it All Begin?
The word “atom” comes from the Greek word “atomos” which means indivisible.
The idea that all matter is made up of atoms was first proposed by the Greek philosopher Democritus in the 5th century B.C.

3. Dalton’s Atomic Theory
John Dalton ( ) proposed an atomic theory
While this theory was not completely correct, it revolutionized how chemists looked at matter and brought about chemistry as we know it today instead of alchemy
Thus, it’s an important landmark in the history of science.

4. Dalton’s Atomic Theory - Summary
matter is composed, indivisible particles (atoms)
all atoms of a particular element are identical
different elements have different atoms
atoms combine in certain whole-number ratios
In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements.

5. Problems with Dalton’s Atomic Theory?
1. matter is composed, indivisible particles
Atoms Can Be Divided, but only in a nuclear reaction
2. all atoms of a particular element are identical
Does Not Account for Isotopes (atoms of the same element but a different mass due to a different number of neutrons)!
3. different elements have different atoms
YES!
4. atoms combine in certain whole-number ratios
YES! Called the Law of Definite Proportions
5. In a chemical reaction, atoms are merely rearranged to form new compounds; they are not created, destroyed, or changed into atoms of any other elements.
Yes, except for nuclear reactions that can change atoms of one element to a different element

6. What about Electrons?
Much of Dalton’s theories are accepted except that atoms are known now to be divisible into sub-particles.
J.J. Thompson discovered electrons in 1897 by performing the cathode ray experiment.
Plum Pudding Model
Cathode Ray tube

7. Physicist James Chadwick confirmed the existence of yet another subatomic particle: the neutron
Chadwick was awarded the Nobel Peace Prize for physics in 1935 and was also awarded the Hughes Model of the Royal Society in His discovery mad it possible to create with a greater mass than uranium in the laboratory. Because of Chadwick's discovery, "nuclear fission" was discovered.

8. Ernest Rutherford wondered how all these particles were put together
Rutherford’s Gold Foil Experiment

9. The modern view of the atom was developed by Ernest Rutherford (1871-1937).

10. Results of foil experiment if Plum Pudding model had been correct.
What Actually Happened

11. Niels Bohr 1925
Niels Bohr applies quantum theory to Rutherford's atomic structure by assuming that electrons travel in stationary orbits defined by their angular momentum.
This led to the calculation of possible energy levels for these orbits and the postulation that the emission of light occurs when an electron moves into a lower energy orbit.

13. The Language of Chemistry
CHEMICAL ELEMENTS -
pure substances that cannot be decomposed by ordinary means to other substances.
Aluminum
Bromine
Sodium

14. The Language of Chemistry
The elements, their names, and symbols are given on the PERIODIC TABLE
How many elements are there?

15. The Periodic Table
Dmitri Mendeleev ( )

16. Glenn Seaborg (1912-1999 ) Discovered 8 new elements.
Only living person for whom an element was named.

17. The Atom An atom consists of a nucleus (of protons and neutrons)
electrons in space about the nucleus.
Electron cloud
Nucleus

18. Copper atoms on silica surface.
An atom is the smallest particle of an element that has the chemical properties of the element.
Copper atoms on silica surface.
Distance across = 1.8 nanometer (1.8 x 10-9 m)

19. ATOM COMPOSITION The atom is mostly empty space
protons and neutrons in the nucleus.
the number of electrons is equal to the number of protons.
electrons in space around the nucleus.
extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water.

20. ATOMIC COMPOSITION Protons (p+) Electrons (e-) Neutrons (no)
+ electrical charge
mass = x g
relative mass = atomic mass units (amu) but we can round to 1
Electrons (e-)
negative electrical charge
relative mass = amu but we can round to 0
Neutrons (no)
no electrical charge
mass = amu but we can round to 1

21. But Why Does The Periodic Table end too quickly
But Why Does The Periodic Table end too quickly? Can’t we just add a proton to the end???
Let’s Watch!

22. Atomic Number, Z
All atoms of the same element have the same number of protons in the nucleus, Z 13
Atomic number Al
Atom symbol
26.981
AVERAGE Atomic Mass

23. Mass Number, A Mass Number (A) = # protons + # neutrons
C atom with 6 protons and 6 neutrons is the mass standard
= 12 atomic mass units
Mass Number (A) = # protons + # neutrons
NOT on the periodic table…(it is the AVERAGE atomic mass on the table)
A boron atom can have A = 5 p n = 10 amu

24. Isotopes-Neutrons Change
Atoms of the same element (same Z) but different mass number (A).
Boron-10 (10B) has 5 p and 5 n
Boron-11 (11B) has 5 p and 6 n
10B
11B

25. Figure 3.10: Two isotopes of sodium.

26. Isotopes & Their Uses
Bone scans with radioactive technetium-99.

27. Atomic Symbols
Show the name of the element, a hyphen, and the mass number in hyphen notation
sodium-23
Show the mass number and atomic number in nuclear symbol form
mass number
23 Na
atomic number

28. Isotopes?
Which of the following represent isotopes of the same element? Which element?
234 X X 235 X 238 X

29. Answer:
234 U 234 Np 235 U 238 U
234 Np is not an isotope of Uranium. 93

30. Counting Protons, Neutrons, and Electrons
Protons: Atomic Number (from periodic table)
Neutrons: Mass Number minus the number of protons (mass number is protons and neutrons because the mass of electrons is negligible)
Electrons:
If it’s an atom, the protons and electrons must be the SAME so that it is has a net charge of zero (equal numbers of + and -)
If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each negative charge, add an extra electron. For each positive charge, subtract an electron (Don’t add a proton!!! That changes the element!)

31. Learning Check – Counting
Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.
12C C 14C
#p+ _______ _______ _______
#no _______ _______ _______
#e- _______ _______ _______

32. Answers
12C C 14C #p
#no #e

33. Learning Check An atom has 14 protons and 20 neutrons.
A. Its atomic number is
1) ) ) 34
B. Its mass number is
C. The element is
1) Si 2) Ca 3) Se
D. Another isotope of this element is
1) 34X 2) 34X 3) 36X

34. Solution An atom has 14 protons and 20 neutrons.
A. It has atomic number
1) 14
B. It has a mass number of
3) 34
C. The element is
1) Si
D. Another isotope of this element would be
3) 36X 14

35. 10B
11B
AVERAGE ATOMIC MASS
Because of the existence of isotopes, the mass of a collection of atoms has an average value.
Boron is 20% 10B and 80% 11B. That is, 11B is 80 percent abundant on earth.
For boron atomic weight
= (10 amu) (11 amu) = amu

36. Isotopes & Average Atomic Mass
Because of the existence of isotopes, the mass of a collection of atoms has an average value.
6Li = 7.5% abundant and 7Li = 92.5%
Avg. Atomic mass of Li = ______________
28Si = 92.23%, 29Si = 4.67%, 30Si = 3.10%
Avg. Atomic mass of Si = ______________

37. Nuclear Chemistry

38. NUCLEAR CHEMISTRY In 1896- Antoine Becquerel discovered radioactivity.
He accidentally left uranium ore on top of photographic plates. They became fogged from exposure to the radiation.
Becquerel had two graduate students: Marie and Pierre Curie.

39. Radioactivity- the property by which uranium gives off rays.
Radiation-penetrating rays emitted by a radioactive source.
In 1903, the Curies and Becquerel won Nobel prizes for this discovery.
Marie Curie is still the only woman to win the Nobel prize in Chemistry and Physics
Types of Radiation Video

40. *Light nuclides are stable when the neutron/proton ratio = 1.
Radioisotopes –are radioactive isotopes that have unstable nuclei.
The stability of a nucleus is determined by its ratio of protons to neutrons. An unstable nucleus loses energy by spontaneously emitting radiation. This is radioactivity.
*All nuclides with atomic numbers greater than or equal to 84 are unstable.
*Light nuclides are stable when the neutron/proton ratio = 1.
*Heavier nuclides are stable when the neutron/proton ratio is greater than 1.
*Nuclides with even numbers of protons and neutrons are more stable than those with odd numbers.

41. Types of Radiation He 2 protons & 2 neutrons = 4 2+ charge
1. alpha () emission -helium nuclei ( )
emitted from a radioactive source
2 protons & 2 neutrons = 4
2+ charge
Don’t travel far and are not very penetrating (stopped by a sheet of paper)
Can’t penetrate skin, but dangerous if ingested
Very common with heavy nuclides He

42. Mass # = # protons + # neutrons Law of conservation of mass
Examples:
Mass # = # protons + # neutrons
238 Th
U  ___ + He 92
Atomic #
222
Ra Rn + He 86
Law of conservation of mass

43. 2. Beta Radiation - fast moving electron formed by the decomposition of a neutron of the atom. (net effect: neutron changes into a proton).
Much smaller than an alpha particle
Symbol is beta or β
Charge is negative 1
Much more penetrating than alpha particles
Stopped by aluminum foil or thin pieces of wood

44. 3. Gamma emission – electromagnetic radiation (high energy) emitted from a nucleus as it changes from an excited state to a ground energy state.
Often emitted along with alpha or beta radiation
Symbol is gamma or γ
Has no charge and no mass
High energy photon
Extremely penetrating, very dangerous
Stopped somewhat by several feet of concrete or several inches of lead.

45. Question
When nuclear power was first developed, people thought they could protect themselves from a nuclear blast by hiding in their basements. Was this a correct assumption?

46. 4. Positron emission – particle with the mass of an electron but with a positive charge.
• antimatter

47. Let’s Sum it Up! Type of radiation Symbol Symbol with mass and charge
Penetration
Alpha α He
Low
Beta β e
Medium
Gamma γ
High
Neutron n
Very High
Positron
Let’s Sum it Up!

48. Let’s Practice Writing Nuclear Equations:+1
Co Ni + ____
Am Np + ____
Th He + ____
N + ____ C + H e 60 26 60 27 4 2 He
241 95
237 93
230 90 4 2
226 88 Ra 1 n 1 14 7 14 6

49. This is the way that heavy elements are created that are added onto the periodic table. How far will it go? Only time and our technology can tell!
Nuclear Transformation (Transmutation)- changing one element into another.
bombarding with alpha particles
Bombarding with neutrons
N He  O H
U n  U