Chemistry Atomic Structure and the Periodic Table

What are the three subatomic particles in an atom and their properties?

• Proton: Charge +1, Mass 1

• Neutron: Charge 0, Mass 1

• Electron: Charge -1, Mass very small

What is the atomic number?

Number of protons in an atom

What is the mass number?

Sum of protons and neutrons in the nucleus

What are isotopes?

Atoms of the same element with different numbers of neutrons

How are electrons arranged in an atom?

In shells:

• 1st shell: 2 electrons

• 2nd shell: 8 electrons

• 3rd shell: 8 electrons

How are elements arranged in the periodic table?

By increasing atomic number

What are groups in the periodic table?

Vertical columns where elements have the same number of outer-shell electrons

What are periods in the periodic table?

Horizontal rows where elements have the same number of electron shells

What is the difference between metals and non-metals?

• Metals: Left side, conduct electricity, form positive ions

• Non-Metals: Right side, do not conduct electricity, form negative ions

What are noble gases (Group 0), and why are they unreactive?

Full outer electron shells, making them inert

What is periodicity?

Repeating patterns in properties across periods

Where are transition metals located in the periodic table?

The center block (between Groups 2 and 3)

What are the key properties of transition metals?

• High melting points (except mercury)

• High densities

• Form colored compounds

• Act as catalysts

• Have variable oxidation states

How do transition metals compare to Group 1 metals?

• Less reactive with water and oxygen

• Harder, stronger, and denser than Group 1 metals

Describe the ‘Plum Pudding’ model.

Atom as a sphere of positive charge with embedded electrons

What did Rutherford’s gold foil experiment prove?

Atoms have a small, dense, positively charged nucleus

What is the modern atomic model?

Electrons orbit in energy levels around a nucleus containing protons and neutrons

Why did Mendeleev leave gaps in the periodic table?

To predict undiscovered elements