1. SECTION III: A WORLD OF PARTICLES
UNIT I: ALCHEMY
SECTION III: A WORLD OF PARTICLES

2. Dalton’s Atomic Theory
In 1808, Dalton proposed a theory to explain the laws of conservation of mass, definite proportions, & multiple proportions.

3. Dalton’s Atomic Theory
All matter is composed of extremely small particles called atoms.
2. Atoms of a given element are identical in size, mass, and other properties.
3. Atoms cannot be subdivided created or destroyed.
4. Atoms of different elements combine in simple whole-number ratios to form chemical compounds.
5. In chemical reactions, atoms are combined, separated, or rearranged.

4. The ATOM
Atom- the smallest particles of an element that retain the chemical properties of that element.
The atom is composed of two main regions, the nucleus & the electron cloud.

5. NUCLEUS
Nucleus- very small region located at the center of the atom. The nucleus accounts for most of an atoms mass but very little volume, making it a very dense region.
The nucleus contains protons & neutrons.

6. ELECTRON CLOUD
The electron cloud is the negatively charged region of the atom that accounts for most of the atoms volume but very little of the atom’s mass.
The electron cloud is composed of electrons.

7. SUBATOMIC PARTICLES
Protons- positively charged particles found in the nucleus of an atom.
Neutrons- neutral particles found in the nucleus of an atom.
Electrons- negatively charged particles found in the electron cloud.

8. IDENTIFYING PROPERTIES OF Atoms
Atomic Number (Z)- the number of protons in the nucleus of each atom of a given element.
Defining characteristic of an element; identifies the element.
Atomic Number increases from left to right on the periodic table.
The atomic number is listed above the element’s symbol on the periodic table.

9. Mass Number
Mass Number (A)- the number of protons & neutrons in the nucleus of an atom.
# of neutrons = Mass Number – Atomic Number

10. ISOTOPE
Isotope- two or more atoms having the same atomic number, but different mass numbers.

11. IDENTIFYING PROPERTIES OF Atoms
Electrons
The number of electrons in a neutral atom is equal to the number of protons in that atom.
Electrons can be lost or gained.
When electrons are lost or gained ions are formed.

12. Isotope Notation Nuclear Notation Hyphen Notation
Uses the elements symbol followed by a hyphen & the mass number.
C-12

13. Average Atomic Mass
Average Atomic Mass- the weighted average of atomic masses of the naturally occurring isotopes of an element.
The atomic mass is expressed relative to the value of exactly 12u for a carbon-12 atom.
Atomic Mass Unit – amu or u

14. Nuclear Reactions
Nuclear reactions involve changes to the nucleus and can change one element to another.
Nucleus can lose particles; nucleus can split into smaller nuclei; or nucleus can combine with another nucleus or particle.
Can be spontaneous.
Occur in the core of stars.

15. RADIOACTIVE DECAY
Radioactive Decay-the process of ejecting or emitting pieces from the nuclei of an atom.
Types of Decay:
Alpha Decay
Beta Decay
Gamma Decay

16. Alpha decay
Alpha Decay- ejection of an alpha particle from the nucleus of an atom.
Alpha particle consists of two protons and two neutrons and can be represented by the Greek letter .
Same as a He-4 nucleus.

17. Beta Decay
Beta Decay- ejection of an electron from the nucleus of an atom.
A neutron splits into a proton and an electron and only the electron is ejected from the nucleus.
Beta particle- the electron ejected from the nucleus which can be represented by the Greek letter .

18. Gamma Rays
Gamma rays- a type of high energy radiation represented by the Greek letter, .
The identity of the atom does not change when gamma rays are emitted.

19. Half Life
The amount of time it takes for half of a sample of a radioactive isotope to decay.
The half life of C-14 is 5730 years.
This means that it will take 5730 years for half of a C-14 sample to decay to N-14.

20. Radiation
The particles emitted during nuclear reactions are forms of radiation.
Fission- splitting apart of a nucleus.
Fusion- the joining of nuclei to form a larger nucleus.

21. NucLear Equations Parent Isotope-the starting isotope.
Daughter Isotope- the resulting isotope.