1. Chapter 17: Properties of Atoms and the Periodic Table
17.1 – Structure of the Atom
17.2 – Masses of Atoms
17.3 – The Periodic Table

2. Symbols
Chemical symbols have one capital letter, or one capital letter plus one or two small letters
For some, the symbol is the first letter(s) of the elements name
Some are named after scientists or for their properties
Some come from Latin
Ex. Argentum – Latin for “silver” (Ag on periodic table)

3. What are atoms?
Atom: the smallest particle of an element that still retains the properties of the element (the element H only has H atoms)
Atoms contain subatomic particles that affect its properties
- nucleus – the center of the atom which contains protons, neutrons, and is surrounded by an electron cloud
- protons – particles w/ a positive electrical charge (1+)
- neutrons – particles that do not have an electrical charge
- electrons – particles with a negative electrical charge (1-)

4. Atomic Model 400 B.C. – idea that atoms make up all substances
Another Greek philosopher proposed that this was incorrect and matter was uniform throughout and not composed of smaller particles
Finally in the 1800s, John Dalton proved that atoms exist
Created the atomic model

5. Atoms
Atoms are neutrally charged because the number of electrons is the same as the number of protons
The atom of a given element may lose or gain electrons yet it still remains the same element
The particles in the nucleus of an atom DO NOT change in a chemical reaction
Chemical reactions occur in the electron cloud

6. Electron Cloud Model – the electron cloud is the area around the nucleus of an atom where its electrons are most likely found
There is an attractive force between electrons and protons
There is a repulsive forces between electrons and electrons/ protons and protons

7. How Much Do These Things Weigh?
Most of the mass of an atom is contained within the nucleus of an atom
Protons and neutrons each have a mass of 1.67 x grams
Electrons have a mass about 2000 times smaller (1,836 exactly), therefore electrons are usually not considered when determining the mass of an atom
***You don’t have to know the exact mass of the particles

8. Quarks
Scientists think electrons are not made of smaller particles – they themselves are one of the most basic types of particles
Protons and neutrons are made up of quarks
There are 6 different quarks
3 quarks held together – proton
Another arrangement of 3 quarks – neutron
Understanding the composition of protons and neutrons is an ongoing effort

9. Protons Identify the Element
Protons identify the elements – If you are given the number of protons an element has in its nucleus, you can determine the name and symbol of the atom
The number of protons in an atom is equal to the atomic number
Example: an element with 7 protons will ALWAYS be Nitrogen (N) and an element with 79 protons will ALWAYS be Gold (Au)
Please give the name and symbol for the following elements 14, 10, 1, 92

10. Further Identifying Atoms
Mass Number = Number of Protons + Number of Neutrons (P+N)
If you know the mass # and the atomic #, you can calculate the # of neutrons
Isotopes – Atoms of the same element that have different numbers of neutrons (will always have the same number of protons)
Ex. Carbon-12 and Carbon-14

11. Practice
Complete the following table (MN = #P + #N)
Element
Symbol #P
Atomic # #N
Mass Number
Silicon
Si-29 14 15 29
Potassium
K-40
Copper
Cu-64
Krypton
Kr-84
Remember the mass number is for a specific isotope and that the number of neutrons = mass number – number of protons

12. Average Atomic Mass
The Atomic mass of an element is the weighted average of the masses of the naturally occurring isotopes of an element.
The atomic mass given on the periodic table is the average atomic mass. Why?
Because there is usually more than one isotope of an given element.

13. Elements
He-4
Symbol of the element
Mass number

14. The Periodic Table
Periodic – something that has a repeated pattern ex. Days of the week, 1st period followed by 2nd period…
Dmitri Mendeleev – placed the known elements of his time in order of increasing atomic mass and found a pattern that repeated – followed predictable changes in physical & chemical properties
Henry G.J. Mosely Improved the Periodic Table by placing elements according to atomic number, how it is today

15. Construction of the Periodic Table
Groups – vertical columns on the periodic table (1-18)
Elements in each group have similar properties
Examples:
Group #1 Hydrogen, Lithium, Sodium, etc. – highly reactive
Group #11 (Copper, Silver, Gold) – shiny metal, good conductor of electricity and heat
Group #18 “The Noble Gases” – non-reactive (except under certain conditions) non-metals

16. Electron Cloud Structure
In a neutral atom, the number of electrons = the number of protons
Electrons closer to the nucleus have lower amounts of energy, electrons further from the nucleus have more energy
Elements in the same group have the same number of outer (valence electrons) which gives them similar properties (similar chemical reactivity)

17. Electron Cloud Structure
There is a specific order in which the energy levels fill
Energy Level 1 fills first with two electrons then it is full
Energy Level 2 fills with eight electrons then it is full
Energy Level 3 fills with eight electrons then it is full
An atom is not stable unless it has a complete outer energy level (8 electrons)

18. Rows on the Periodic Table
Periods on the periodic table of the elements run horizontally across the table
Period numbers represent the number of energy levels an atom has

19. Regions (Families) on the Periodic Table of The Elements
Alkali Metals (Group 1)
Alkaline Earth Metals (Group 2)
Transition Metals (Groups 3-12)
Metalloids (Stair step Line)
Non-Metals (To the Right of the stairs)
Noble gases (Group 18)
Lanthanide Series (Elements 58-71)
Actinide Series (Elements Radioactive)

20. Valence Electrons
The number of electrons in the outer-most energy level are called valence electrons
Group
Name
# valence electrons 1
Alkali Metals 2
Alkaline Earth Metals 13 3 14 4 15 5 16
Oxygen Group 6 17
Halogens 7 18
Noble Gases
8 (except He)

21. Trend in The Periodic Table
Trends in the number of valence electrons
From L to R
From Top to Bottom
Trends in the number of energy levels
From left to right across any period
From top to bottom within any group

22. Atoms
Stable atoms contain 8 valence electrons – If an atom does not have 8, it tends to gain, lose, or share valence electrons to become stable
Group 1 & 2 : lose 1 and 2 electrons, respectively
Group 18 : stable, do not readily gain/lose
Group 16 & 17 : gain 2 and 1 electrons, respectively
Group 13-15: less likely to gain/lose
Most transition elements (Groups 3-12) : tend to lose electrons