1. the smallest particle of an element
Atom
the smallest particle of an element

2. the dense, positively charged mass located in the center of an atom
Nucleus
the dense, positively charged mass located in the center of an atom

3. Proton
a positively charged subatomic particle that is found in the nucleus of an atom

4. a neutral subatomic particle that is found in the nucleus of an atom
Neutron
a neutral subatomic particle that is found in the nucleus of an atom

5. Electron
a negatively charged subatomic particle that is found in the space outside the nucleus of an atom

6. A term that means 'smaller than an atom'
Subatomic
A term that means 'smaller than an atom'

7. a very small piece of something
Particle
a very small piece of something

8. Thomson The man who discovered the electron.
This disproved one important point of Dalton's atomic theory:
Atoms cannot be subdivided, created, or destroyed.
The Plum Pudding model of the atom by Sir Thomson clearly differentiated between the positive and negative regions of an atom

9. Dalton Created the atomic theory:
Dalton’s Model
Dalton
Created the atomic theory:
All matter is composed of small particles called atoms
All atoms of a given element are alike
Compounds are formed when different atoms combine in fixed proportions
A chemical reaction involves the rearrangement of atoms

10. Rutherford The man who discovered the nucleus of an atom.
The Rutherford model of the atom was simplified in a well known symbol showing electrons circling around the nucleus like planets orbiting the sun.
The element 'rutherfordium' was named in Rutherford’s honor.

11. Gold Foil Experiment
The experiment conducted by Ernest Rutherford to discover the nucleus of an atom.

12. Isotopes
The term given to atoms of the same element that have different numbers of neutrons.

13. Half-life
In atoms that are radioactive, the time required for half of the element to decay.

14. To break into smaller pieces.
Decay
To break into smaller pieces.

15. Bohr The man who discovered electron energy levels.
The Bohr model shows that the electrons in atoms are in orbits of differing energy around the nucleus (think of planets orbiting around the sun).
Bohr used the term energy levels (or shells) to describe these orbits of differing energy.

16. Electron Cloud Model The current model for atomic structure.
No way to know exactly where an electron is at any moment in time.
We can only approximate, or guess, where an electron is located.
According to something called quantum theory, an electron can be found anywhere around the nucleus.  

17. Element
A form of matter that cannot be separated into simpler substances by ordinary chemical methods.

18. Energy Levels the possible energies that electrons in an atom can have
Energy Level (Principal Quantum Number)
Shell Letter
Electron Capacity 1 K 2 L 8 3 M 18 4 N 32 5 O 50 6 P 72

19. Mass Number
the sum of the number of protons and neutrons in the nucleus of an atom

20. Atomic Number
a unique number for each element that equals the number of protons in an atom of that element

21. Periodic Table
an arrangement of elements in columns based on a set of properties that repeat from row to row

22. When a column goes from top to bottom, it's called a group.
The elements in a group have the same number of electrons in their outer orbital.
Those outer electrons are also called valence electrons. They are the ones involved in chemical bonds with other elements. 

23. Periods each of the rows is considered to be a different period.
In the periodic table, elements have something in common if they are in the same row. All of the elements in a period have the same number of atomic orbitals.
Every element in the top row (the first period) has one orbital for its electrons. All of the elements in the second row (the second period) have two orbitals for their electrons.
At this time, the maximum number of electron orbitals or electron shells for any element is seven. 

24. Periodic Law
 physical and chemical properties of the elements recur in a systematic and predictable way when the elements are arranged in order of increasing atomic number.

25. Metals elements that are good conductors of heat and electric current
Almost 75% of all elements are classified as metals.
What are the characteristics of metals? 
Conduction
Reactivity
Chemical
Alloys

26. Non Metals Nonmetals share many similar properties including:
They are either gas or solid under standard conditions.
They are very brittle in their solid form.
They are not malleable or ductile.
They generally have lower densities than metals.
Poor conductors of heat and electric currents

27. Noble Gases the elements in Group 8A of the periodic table
They are located to the far right of the periodic table.
Elements in the noble gas family have atoms with a full outer shell of electrons.
They are also called the inert gases

28. Halogens the elements in Group 7A of the periodic table
have seven electrons in their outer shell. That seven-electron trait applies to all of the halogens.
 they have the trait of combining with many different elements.
They are very reactive. You will often find them bonding with metals and elements from Group One of the periodic table.

29. Alkali Metals
the elements in Group 1A of the periodic table, not including hydrogen
They are very reactive.
They all have one electron in their outer shell. That's one electron away from being happy (full shells).
An increased desire to bond means you are more reactive.
some of these pure elements in water (H2O), can cause huge explosions. 
They are malleable (bendable) and sometimes soft enough to be cut with a dull knife.
Hydrogen not included

30. Alkali Earth Metals the elements in Group 2A of the periodic table
This is the second most reactive
they are likely to form solutions with a pH greater than 7
Each of them has two electrons in their outer shell. They are ready to give up those two electrons in electrovalent/ionic bonds

31. Metalloids
elements with properties that fall between those of metals and nonmetals
 found along the stair-step line that distinguishes metals from non-metals.
Metalloids have properties of both metals and non-metals.
Some are semi-conductors. This means that they can carry an electrical charge under special conditions

32. Octet Rule
atoms will readily bond with other atoms to have 8 electrons in the outer shell
Atoms tend to gain, lose or share one or more of their valence electrons to achieve a filled outer electron shell

33. Ion a charged atom, with more or less electrons than neutrons.
Cations are ions with a net positive charge. Examples : Silver: Ag+, hydronium: H3O+, and ammonium: NH4+
Anions are ions with a net negative charge. Examples: hydroxide anion: OH- , oxide anion: O2-, and sulfate anion: SO42-
Lost Electron
Gained Electron

34. Valence Electrons
An atom's number of electrons occupying the last outermost shell..
In general, the number of valence electrons of a element is equal to the group number  

35. Dmitri Mendeleev Father of the Periodic Table
arranging the 63 known elements into a Periodic Table based on atomic mass
arranging the elements in ascending order of atomic weight and grouping them by similarity of properties.  
He predicted the existence and properties of new elements and pointed out accepted atomic weights