1. Chapter 17
Properties of atoms & the periodic table 0

2. Section 1: structure of the atom
Each element has a chemical symbol
Chemical symbol: consists of one capital letter OR one capital letter + one or two lower case letters H Na
System is universal
Everyone knows what they mean!

3. Atomic components
Atom- the smallest piece of matter that retains the properties of the element
Atoms are composed of protons, neutrons, and electrons
Protons and neutrons are found in the nucleus
Protons- particles with a charge of +1
Neutrons- neutral particles (no charge)
Electrons- particles with a charge of -1

4. Models of the atom Difficult to visualize
This is what models are for!
Democritus (B.C.)
1800s John Dalton proved atoms existed
Solid spheres
The model of the atom is ever changing

5. Electron cloud is much larger than the nucleus
The electron cloud
Electrons are found in an electron cloud
Electron cloud- the area around the nucleus where electrons are likely found
Electron cloud is much larger than the nucleus

6. Review What is the charge of a proton?
What is the charge of a neutron?
What is the charge of an electron?
What is in the nucleus?
What determines the atomic number?
Where does the mass of an atom come from?

7. Section 2: Masses of atoms
Most of the mass of an atom is in the nucleus
Protons and neutrons are approx. the same size
Electrons are much smaller

8. Atomic number
Atomic number—the number of protons in an atom. (always a whole number)
Atoms of different elements have different #’s of protons & different atomic #’s.
The atomic # of an element is on the periodic table

9. Mass number
Mass Number—the sum of the # of protons & the # of neutrons
Mass # = # of neutrons + atomic #
If you know mass # & atomic # you can find the # of neutrons.
# of neutrons = Mass # - Atomic #
Not all atoms of the same element have the same # of neutrons

10. isotopes Different isotopes of elements have different properties.
Isotopes—atoms of the same element with different numbers of neutrons
Different isotopes of elements have different properties.
You can distinguish isotopes by writing the name of the element followed by the mass #.
Ex. Carbon-12 and Carbon-14
Each element has an average atomic mass.

11. Atomic mass
Average atomic mass (or atomic mass)—the weighted average mass of the mixture of isotopes. (found on the periodic table)
Atomic mass is always closest to the most abundant isotope.

13. Section 3: The periodic table
Periodic Table— an organized list of all known elements that are arranged according to their properties
The 1st person to organize elements was Dmitri Mendeleev in the 1800s
Mendeleev organized the elements by their atomic mass and left spaces for unknown elements.

14. The modern periodic table
Mendeleev’s table was mostly correct, but it is more accurate to organize elements in order of increasing atomic number.

15. groups Groups (or families)— vertical columns on the periodic table.
They are numbered 1-18.
Elements in each group have similar properties.

16. periods Periods—horizontal rows of elements on the periodic table.
Periods are numbered 1-7
Elements increase by one proton as you move from left to right across a period.

17. Electrons and the periodic table
The periodic table organizes elements based on where their electrons are located. 1
Electrons (e-)—are located in different energy levels around the nucleus. 2
Elements in the same group have electrons arranged similarly which gives them similar properties. 3

18. Electron shells
The number of energy levels or electron shells is determined by the period number.
Period 1: 1 electron shell and can hold 2 e-
Period 2: 2 electron shells & can hold 8 e-
Period 3: 3 electron shells & can hold 8 e-
As you move down the periodic table, 1 electron shell is added each time.
The outer electron shell must be full (usually with 8 e-) to be stable.

19. Electron dot diagrams
You can show the number of electrons in the outermost electron shell by using an electron dot diagram.
Dot diagrams use valence electrons which are the electrons in the outer electron shell.
Electron Dot Diagram—uses the symbol of the element and dots to represent the valence electrons.