1. Modern Periodic Table 5.2

2. The Periodic Law
In the modern periodic table, elements are arranged by increasing atomic number (number of protons)
Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups. This is called periodic law.

3. PARTS OF THE PERIODIC TABLE
Period – horizontal row
Group – vertical columns; they are numbered 1 – 18
Family – specific name describing one or more groups; ex: Column 18 is the noble gases
Elements in the same group have the same number of valence electrons (electrons in their outer shell)

4. Atomic Mass
Atomic mass depends on the distribution of an element’s isotopes in nature and the masses of those isotopes.
The atomic mass in grams is extremely small, so scientists developed a unit based on the carbon atom
Atomic mass unit (amu) – equal to 1/12 the mass of a carbon-12 atom

5. CLASSES OF ELEMENTS Metals – left and center part of periodic table
Conduct heat and electricity, have luster, malleable,
ductile
All are solid at
room temperature
(except mercury)

6. CLASSES OF ELEMENTS Transition elements – groups 3 – 12
They are metals
Unpredictable reactivity and properties

7. CLASSES OF ELEMENTS Lanthanides – atomic number 57 – 70
a. Rare earth elements – less than 0.01% of the elements found on Earth

8. CLASSES OF ELEMENTS Actinides – Atomic number 89 – 102 All radioactive
Only 90, 91, and 92 occur naturally

9. CLASSES OF ELEMENTS Nonmetals – right side of the periodic table
Very abundant in nature
Poor conductors of electricity and heat, brittle, many are gases

10. CLASSES OF ELEMENTS
Metalloids – some properties of metals and some properties of nonmetals
They are found along the border between metals and nonmetals
They are semiconductors

11. Exception to periodic law
Hydrogen is placed in group 1, even though it is a gas.
Hydrogen’s location is related to its valence electrons, not its properties
Elements in a group have similar properties because they have the same number of valence electrons
Valence electrons determine how reactive an atom is.