Modern Periodic Table Modern Periodic Table 5.25.2

The Periodic LawThe Periodic Law

1.1. In the modern periodic table, In the modern periodic table, elements are arranged by elements are arranged by increasing atomic number (number increasing atomic number (number of protons)of protons)

2.2. Properties of elements repeat in a Properties of elements repeat in a predictable way when atomic predictable way when atomic numbers are used to arrange numbers are used to arrange elements into groups. This is called elements into groups. This is called periodic law.periodic law.

PARTS OF THE PERIODIC TABLEPARTS OF THE PERIODIC TABLE

1.1. Period – horizontal rowPeriod – horizontal row2.2. Group – vertical columns; they are Group – vertical columns; they are

numbered 1 – 18numbered 1 – 183.3. Family – specific name describing Family – specific name describing

one or more groups; ex: Column 18 one or more groups; ex: Column 18 is the noble gasesis the noble gases

4.4. Elements in the same group have the Elements in the same group have the same number of valence electrons same number of valence electrons (electrons in their outer shell)(electrons in their outer shell)

Atomic MassAtomic Mass

1.1. Atomic mass depends on the Atomic mass depends on the distribution of an element’s isotopes in distribution of an element’s isotopes in nature and the masses of those nature and the masses of those isotopes.isotopes.

2.2. The atomic mass in grams is extremely The atomic mass in grams is extremely small, so scientists developed a unit small, so scientists developed a unit based on the carbon atombased on the carbon atom

3.3. Atomic mass unit (amu) – equal to 1/12 Atomic mass unit (amu) – equal to 1/12 the mass of a carbon-12 atomthe mass of a carbon-12 atom

CLASSES OF ELEMENTSCLASSES OF ELEMENTS

1.1. Metals – left and Metals – left and center part of center part of periodic tableperiodic table

a.a. Conduct heat and Conduct heat and electricity, have electricity, have luster, malleable, luster, malleable,

ductileductile

b.b. All are solid atAll are solid at

room temperatureroom temperature

(except mercury)(except mercury)

CLASSES OF ELEMENTSCLASSES OF ELEMENTS

2.2. Transition Transition elements – elements – groups 3 – 12groups 3 – 12

a.a. They are metalsThey are metals

b.b. Unpredictable Unpredictable reactivity and reactivity and propertiesproperties

CLASSES OF ELEMENTSCLASSES OF ELEMENTS

3.3. Lanthanides – Lanthanides – atomic number atomic number 57 – 7057 – 70

a. Rare earth a. Rare earth elements – less elements – less than 0.01% of the than 0.01% of the elements found on elements found on EarthEarth

CLASSES OF ELEMENTSCLASSES OF ELEMENTS

4.4. Actinides – Actinides – Atomic number Atomic number 89 – 10289 – 102

a.a. All radioactiveAll radioactive

b.b. Only 90, 91, and Only 90, 91, and 92 occur naturally92 occur naturally

CLASSES OF ELEMENTSCLASSES OF ELEMENTS

5.5. Nonmetals – right Nonmetals – right side of the side of the periodic tableperiodic table

a.a. Very abundant in Very abundant in naturenature

b.b. Poor conductors of Poor conductors of electricity and electricity and heat, brittle, many heat, brittle, many are gasesare gases

CLASSES OF ELEMENTSCLASSES OF ELEMENTS

6.6. Metalloids – some Metalloids – some properties of properties of metals and some metals and some properties of properties of nonmetalsnonmetals

a.a. They are found They are found along the border along the border between metals between metals and nonmetalsand nonmetals

b.b. They are They are semiconductorssemiconductors

Exception to periodic lawException to periodic law

1.1. Hydrogen is placed in group 1, even Hydrogen is placed in group 1, even though it is a gas.though it is a gas.

2.2. Hydrogen’s location is related to its Hydrogen’s location is related to its valence electrons, not its propertiesvalence electrons, not its properties

3.3. Elements in a group have similar Elements in a group have similar properties because they have the properties because they have the same number of valence electronssame number of valence electrons

4.4. Valence electrons determine how Valence electrons determine how reactive an atom is.reactive an atom is.