1. The Building Blocks of Matter: Atoms- - - + + + + - - + + - - -

2. Atoms
Atoms are the smallest part of an element that has all the Characteristics of the element.
If you break an atom apart into sub-atomic particles, they no longer have the properties of the element.

3. Atoms
Smallest possible unit into which matter can be divided, while still maintaining its properties.
Made up of:
protons
neutrons
electrons
The solar system is commonly used as an analogy to describe the structure of an atom - +
For example, what is the
smallest possible unit
into which a long essay can be
divided and still have some meaning? - + + - + + - -

4. Two major parts of an atom
Nucleus (not to scale)
Electron Cloud

5. + The Atom’s “Center” - - -
Protons and neutrons are grouped together to form the “center” or nucleus of an atom.
Notice that the electrons are not apart of the nucleus + - - -

6. Most space between nucleus and electron cloud is empty space.

7. Nucleus: Center 1. Protons and
Where are they located?
Nucleus: Center Protons and
2. Neutrons

8. Review: Subatomic ParticlesN°  e-

9. PROTON (p+)
positive charge a single, relatively large particle (mass) with a that is found in the nucleus

10. p+ THE PROTON Fat (heavy, large mass) Positive  (charge)
Doesn’t move (lazy) stays in nucleus

11. Every atom of an element has the same number of protons
Every atom of an element has the same number of protons. Carbon atoms always have 6 protons Hydrogen atoms always have 1 proton Uranium atoms always have 92 protons. How many protons does Helium have? __________

12. NEUTRON (N°)
a single, relatively large particle with a neutral charge that is found in the nucleus

13. THE NEUTRON N° 
Fat (heavy)
Neutral  (charge)
Doesn’t move (lazy)

14. Number of neutrons in an element can change
Number of neutrons in an element can change. It is just like gaining or losing weight. It doesn’t change what the element is- just how much it weighs.(Mass number)

15. ELECTRON (e-)
a single, very small (Mass) particle with a negative charge that is found in a “cloud” around the nucleus

16. e- THE ELECTRON Skinny (very light) Negative  (charge)
Moves a lot (runs around)

17. Oxygen (O) Atom
Notice the two electrons in the first orbital/level and the six in the second + -
= 8
How many
more electrons
can fit in the 2nd
orbital/ level? - - - + + + + - - + + - - -

18. Electron Orbitals…
Electrons are what determines how an atom chemically reacts.
Electron Cloud:- areas within atoms where there is a high probability of finding electrons.

19. Energy Levels 3rd shell- 8 electrons
1st energy is closet to the nucleus- it can only ever hold 2 electrons.
2nd shell- 8 electrons
3rd shell- 8 electrons
Electrons will always fill shells closet to the nucleus first.

20. Sodium (Na) Atom
Notice the two electrons in the first orbital/level, eight in the second, and one in the third + -
= 11
= 12 - - -
How many
more electrons
can fit in the 3rd
orbital/ level? - + + + + - - - + + - - - -

21. Because of this unknown we call the orbitals an “electron cloud”
Science has determined where the orbitals are inside an atom, but it is not know precisely where the electrons are inside the orbitals.
Because of this unknown we call the orbitals an “electron cloud”
Knowing how electrons are arranged in an atom is important because that controls how atoms react with each other to form compounds.

22. Three Major Sub-Atomic Particles
Protons
Neutrons
Electrons

23. ATOMIC MASS #
(A)
The total mass of all of the subatomic particles in an atom (but really # of protons and neutrons)

24. ATOMIC NUMBER (Z)
the number of protons in an atom (assuming the atom is neutral, # of p+ = # of e-)

25. Example: Sodium Na Atomic Mass # = p+ & N° 22.99 11
Atomic # = # of protons

26. Another Notation
Atomic Mass # = p+ & N°
Atomic # = # of protons

27. To calculate the number of neutrons, subtract the atomic number (smaller) from the atomic mass number (larger) A – Z = # of neutrons

28. Ex: How many neutrons does Sodium have?
Mass # - Atomic # = #N°
(You may need to round the atomic #)
22.99
= 12 N° Na 11

29. ELEMENTS
Elements are electrically neutral. (They have the same # of p+ and # of e-)

30. ION
Atoms of the same element that differ in charge. (They have the same # of p+, but different # of e-)

31. Ex: How many electrons does Sodium have?
The atomic number equals the number of protons and the number of electrons.
22.99
11 electrons Na 11

32. Positive Ions (cations)
Negative Ions (anions)
Na+ (lost 1 e-)
Ca2+ (lost 2 e-)
Al3+ (lost 3 e-)
Pb4+ (lost 4 e-)
H+ (lost 1 e-)
Cl- (gain 1 e-)
O2- (gain 2 e-)
P3- (gain 3 e-)
S2- (gain 2 e-)
OH- (gain 1 e-)

33. If an atom GAINS electrons, its overall charge becomes more negative
If an atom GAINS electrons, its overall charge becomes more negative. If it LOSES electrons, its charge becomes more positive

34. ISOTOPE
Atoms of the same element that differ in mass. (They have the same # of p+, but different # of N°)

35. Isotopes are CHEMICALLY the SAME as atoms, but DIFFER PHYSICALLY because they have different masses.

36. A few examples of isotopes…

37. So, why do the elements on the PT have masses with decimals???

38. The average mass of all of the isotopes of a substance
AVERAGE ATOMIC MASS
The average mass of all of the isotopes of a substance

39. Example using exam scores!

40. Example using exam scores!
Exam Scores can be weighted higher than homework or quiz grades:
What if…
Exam 50%
Quizzes 20%
Homework 30%
And you received:
Exam 90
Quizzes 80
Homework 70
Your grade = (90 x .5) + (80 x .2) + (70 x .3) = 82

41. To calculate the average atomic mass:
Mass each isotope and multiply by # present
Add these products
Divide this sum by the total # present

42. Famous Scientists in Atomic Theory

43. Democritus (400 B.C.)
World is made of 2 things: empty space “atoms”

44. democritous

45. (Law of Conservation of Mass)
LAVOISIER
Found out that the mass of the products must equal the mass of the reactants
(in a closed system)
(Law of Conservation of Mass)

46. PROUST LAW OF DEFINITE PROPORTIONS
Specific substances always contain elements in the same ratio BY MASS

47. DALTON LAW OF MULTIPLE PROPORTIONS
The ratio of masses of 1 element that combine with a constant mass of another element can be expressed in whole numbers