1. The Periodic Table
Science 9, 2016

2. Introduction
By the 1780’s chemists wondered why some elements were gas whereas others were metals
By the 1860’s the list of known elements had grown to 63
Chemists were searching for a pattern among those elements
In 1867, Dmitri Medeleev proposed organizing the elements into a table based on their properties
He gathered information on the elements and put it on cards
He then sorted the cards into rows and columns

3. Introduction Cont’d Mendeleev started noticing patterns
All the cards that were metals ended up one side
All the non-metals ended up on the other side
Metalloids were in the middle
Most of the elements that were gasses at room temp were grouped together
Mendeleev was so confident in his table that he left spaces open for elements that had not been discovered yet
In 1886 germanium was discovered and the properties were an exact match to an open space on the table
Henry Moseley rearranged the table based on atomic number

4. Modern Periodic Table
Elements are listed from left to right and top to bottom according to their atomic number
Moseley proposed that atoms of the same element could have different masses
These are called isotopes
Periodic Law: description stating that elements arranged in order of atomic mass show a periodic repetition of properties

5. Atomic Number
Atomic number of an element is defined as the number of protons in the nucleus of an element
Lowest atomic number is 1 (Hydrogen)
Atomic number of Helium is 2
Atomic number of Carbon is 6
The number of protons in the nucleus of an atom, or the atomic number, determines the atom
No one knows what the highest possible atomic number is, but of it was 118

6. Atomic Mass The average mass of an elements atoms
Measured in atomic mass units (amu)
Atomic mass of hydrogen is 1.01 amu and the atomic mass of iron is amu. What does this mean?
Atomic mass usually increases in order of increasing atomic numbers.
However, there are some exceptions. Iodine has a lower amu than tellurium

7. Ion Charge
Ion charge is the electric charge that an atom takes on when it loses or gains an electron
Elements that can form similar ions are grouped together
Example: Elements in the first column on the left side of the periodic table form a 1+ ion

8. Transition Metals The elements in the middle of the periodic table
Include common metals such as iron, copper, zinc, silver, and mercury
The ion charge cannot be predicted from atomic theory

9. Periods and Chemical Families
Each horizontal row is called a period
The number on the left side of the table identifies each period
There are 18 vertical columns and each one represents a different group or chemical family
Elements within a family or group share certain or physical properties
We discuss alkali metals, halogens, and noble gases

10. Alkali Metals (Li, Na, K, Rb, Cs)
Similarities
Silver-grey metals
Are malleable and ductile and conduct electricity
Have low melting points compared to other metals
Soft enough to cut with a knife
React easily with water and air
Differences
Regular increase in density as you move from top to bottom
Elements also get softer and easier to cut

11. Halogens (F, Cl, Br,I) Similarities: Differences: All are non-metals
All are reactive
All have a distinct colour
Differences:
The colours grow in intensity as you go down the periodic table
Melting points also gradually increase

12. Noble Gases (He, Ne, Ar, Kr, Xe, Rn)
Similarities:
All exist naturally as colorless gasses
Will glow with bright colors if a current is passed through them
None are chemically reactive
Differences
Density of the gases increases steadily

13. The Nucleus At the center of the atom
Comprised of protons and neutrons
The number of protons tells you what atom it is
Number of neutrons can vary
Contains 99.99% of the mass of an atom

14. Protons Have a positive charge
ALWAYS equal to the atomic number of the element
Found in the nucleus

15. Neutrons Have a neutral charge
Equal to: (the atomic mass - number of protons)
Found in the nucleus

16. Electrons Have a negative charge
Surround the nucleus in different energy levels
Inner most level hold two electrons and the next two levels each hold 8 electrons
Can move between energy levels when energy is applied or removed form the atom
Number and arrangement in outermost energy level determines chemical properties of atoms and physical properties of atoms and physical properties of elements
Often exist in pairs

17. Steps for Drawing Atoms
Determine what atom you are drawing
Determine the overall charge of the atom you are drawing
Determine the number of electrons in the atom
Fill the first energy level with two electrons
Fill the second energy level with a maximum of 8 electrons
Continue filling energy levels with a maximum of 8 electrons