1. Properties of Atoms and the Periodic Table
Chapter 18
Properties of Atoms and the Periodic Table

2. Scientific Shorthand
Scientists use abbreviations to write the name of elements.
Abbreviations are easier to write than the whole element.
For example:
Carbon is written as
Aluminum is written as
Silver is written as C Al Ag

3. Scientific Shorthand
The first letter in the symbol is ALWAYS written with a capital letter.
If there is a second letter, it is ALWAYS written as a lowercase letter.
Some element symbols are based on their English names, while others are based on their Latin names.
Silver is Ag from its Latin name Argentum.

4. Atoms Elements are made of atoms
Atoms are the smallest piece of matter that still retains the properties of the element.

5. Subatomic Particles Each atom is made up of smaller particles.
In the center of the atom is the nucleus.
The nucleus is made of protons and neutrons.

6. Subatomic Particles Each atom is made up of smaller particles.
Electrons orbit around the nucleus

7. Subatomic Particles Properties of Protons Properties of Neutrons
Electrical charge of +1
Mass =1 amu.
Properties of Neutrons
Electrical charge of 0.
Properties of Electrons
Electrical charge of -1
Mass is approximately 1/1800 of a proton.

8. Quarks
Protons, neutrons and electrons are all made up of even smaller particles called quarks.

9. Quarks
To study quarks, scientists smash atoms together to break the protons apart.

10. Quarks
Based on the data collected, they can reconstruct the structure of the atom.

11. The Atomic Model - History
Democritus (400 B.C.)
First proposed that atoms made up all substances.
Aristotle
Believed that matter is uniform throughout.
This idea lasted for about 2,000 years.

12. The Atomic Model - History
Dalton’s Model
Each atom was a solid sphere.
Allowed scientists to explain how chemical reactions occurred.
Thomson, Rutherford, and Bohr
Each scientist’s experiments helped to identity different parts of the atom and the structure of the atom.

13. Atomic Model

14. Electron Cloud Model The most current model of the atom.
The electron cloud is 100,000 times larger than the diameter of the nucleus, but each electron is smaller than the proton.
Electrons are so small, and moving so fast, that they are difficult to find.

15. What holds the Nucleus Together?
Protons in the nucleus both
repel and attract each other.
The repulsions are due to
electromagnetic force and
the attractions are due to the
strong nuclear force. The
strong nuclear force only
acts over very short
distances, about the size of
an atomic nucleus. Neutrons
and protons also attract each
other because of the strong
nuclear force.

16. Atomic Masses Most of the mass of an atom is within the nucleus.
Protons and neutrons each weigh about x kg.
That’s kg!
Electrons are 1/1800 of the mass of a proton or neutron.

17. Atomic Masses
To measure atomic mass, we use the “atomic mass unit” or amu.
Mass of 1 proton = 1 amu
Mass of 1 neutron = 1 amu

18. Atomic Number The number of protons in an atom identify the element.
Each element has a different number of protons.
Atoms with 8 protons are always oxygen.
Atoms with 6 protons are always carbon.
Atoms with 16 protons are always sulfur.
The number of protons in an atom is called the atomic number.

19. Atomic Number Practice
Use your periodic table to find the atomic number of the following elements:
Aluminum (Al)
Titanium (Ti)
Tin (Sn)
Osmium (Os)
Erbium (Er)
How many protons does each atom have?
The number of protons are equal to the atomic number.
Al = 13
Ti = 22
Sn = 50
Os = 76
Er = 68

20. Mass Number
The mass number of an atom is the sum of the number of protons and neutrons in the nucleus.
Element
Protons
Neutrons
Mass Number
Boron 5 6
Carbon
Oxygen 8
Sodium 11 12
Copper 29 34
5+6 11
6+6 12
8+8 16
11+12 23
29+34 63

21. Using the Atomic Number & Mass Number
If you know the atomic number and mass number, you can determine the number of neutrons.
Mass Number
- Atomic Number
Number of Neutrons

22. Practice
Determine the number of protons and neutrons in the following atoms:
Lithium – Atomic Number = 3
Mass Number = 7
Argon – Atomic Number = 18
Mass Number = 39
Strontium – Atomic Number = 38
Mass Number = 88

23. Answers
Determine the number of protons and neutrons in the following atoms:
Lithium – Protons = 3
Neutrons = 7 – 3 = 4
Argon – Protons = 18
Neutrons = 39 – 18 = 21
Strontium – Protons = 38
Neutrons = 88 – 38 = 50

24. Isotopes
Atoms of one type of element must have the same number of protons.
However, they can have different numbers of neutrons.
Atoms with the same number of protons and different numbers of neutrons are called isotopes.

25. Isotopes Examples Carbon-12 has a mass of 12 amu.
All carbon atoms must have 6 protons.
Neutrons = 12 – 6 = 6.
C-12 has 6 protons and 6 neutrons.
Carbon-14 has a mass of 14 amu.
Neutrons = 14 – 6 = 8.
C-14 has 6 protons and 8 neutrons.

26. Isotopes Examples Uranium-235 has a mass of 235 amu.
All uranium atoms must have 92 protons.
Neutrons = 235 – 92 = 143.
U-235 has 92 protons and 143 neutrons.
Uranium-238 has a mass of 238 amu.
Neutrons = 238 – 92 = 146.
U-238 has 92 protons and 146 neutrons.

27. Average Atomic Mass
Because atoms can have different numbers of neutrons, the mass numbers can be different.
To get an overall mass of one element, we take the weighted-average of all the isotopes and determine the average atomic mass for the element.

28. Neutral Atoms In the nucleus, which particles have charge?
Protons
What charge do they have?
Positive
What particle is opposite that charge?
Electrons

29. Neutral Atoms
To balance the charges in the atom, the number of protons must equal the number of electrons.
Li has 3 protons, so the nucleus has a charge of +3.
To balance that charge, there must be 3 electrons that add up to -3.
Overall, the charge is (+3) + (-3) = 0, so the atom is neutral.

30. Practice Determine how many electrons the following atoms have:
Magnesium, Protons = 12
Beryllium, Protons = 4
Nitrogen, Atomic Number = 7
Bromine, Atomic Number = 35
12 Electrons
4 Electrons
7 Electrons
35 Electrons

31. Practice Iodine I 53 127 Mercury Hg 80 201 Neon 10 20 Mg 12 Rb 37 48
Element
Symbol
Atomic Number
Mass Number
Protons
Neutrons
Electrons
Iodine I 53
127
Mercury Hg 80
201
Neon 10 20 Mg 12 Rb 37 48 41 51 75
111

32. Practice Iodine I 53 127 74 Mercury Hg 80 201 121 Neon Ne 10 20 Mg 12
Element
Symbol
Atomic Number
Mass Number
Protons
Neutrons
Electrons
Iodine I 53
127 74
Mercury Hg 80
201
121
Neon Ne 10 20
Magnesium Mg 12 24
Rubidium Rb 37 85 48
Niobium Nb 41 92 51
Rhenium Re 75
186
111

33. Bohr Models of the Atoms
Each atom had orbitals or shells in which the electrons can fit.
1st Shell: up to 2 electrons can fit
2nd Shell: up to 8 electrons can fit
3rd Shell: up to 18 electrons can fit
4th Shell: up to 32 electrons can fit
Must start with the smallest/closest orbital or shell first.

34. Drawing Bohr Models Hydrogen Boron AN = 1 AM = 1 e- = 1 AN = 5 AM = 11
1 p+, 0 no
AN = 1
AM = 1
e- = 1
5 p+, 6 no
Boron
AN = 5
AM = 11
e- = 5

35. Drawing Bohr Models
Chlorine
AN = 17
AM = 35
e- = 17
17 p+, 18 no

36. Electron Dot Diagrams Write the symbol of the element
Determine the number of valence electrons (electrons in the outermost energy level)
Start placing valence electrons around the symbol
Pair electrons only after all four sides (top, bottom, left, right) have been used once

37. H H H H Example: Hydrogen Hydrogen has 1 valence electron
Chose one side, and place the electron H H H H OR OR OR

38. Cl Example: Chlorine Chlorine has 7 valence electrons
Place one on each side first
Then begin to pair the remaining electrons Cl

39. N Example: Nitrogen Nitrogen has 5 valence electrons
Place one on each side first
Then begin to pair the remaining electrons N

40. Be Example: Beryllium Beryllium has 2 valence electrons
Place each electron on different sides Be

41. He Example: Helium Helium has 2 valence electrons
Helium is an EXCEPTION
Pair the two electrons because the energy level can only 2 electrons He

42. Periodic Law
Scientists Julius Lothar Meyer and Dmitri Mendeleev individually produced classification schemes for elements in 1869.
Periodic Law: When elements are arranged in order of increasing atomic numbers, elements with similar chemical properties will occur at regular (periodic) intervals.

43. Periodic Table
The rows on the periodic table are separated into periods.

44. Periodic Table
As chemists worked on determining which substances were elements, they noticed that some elements acted very much like other elements. For example, one atom of some metals always reacts with two atoms of oxygen. Chemists called these similar elements a group of elements.

45. Periodic Table

46. Regions of the Periodic Table
Metals: Elements to the lower left side of the periodic table.
Nonmetals: Elements to the upper right of the periodic table.
Metalloids: Elements in between the metals and nonmetals.

47. Metalloids 1 2 18

48. Metals 1 2 18
Hydrogen is an exception

49. Nonmetals 1 2 18
Hydrogen is an exception