Material Science Chapter 2

Atomic Structure and Interatomic Bonding

What are the three main subatomic particles?

Protons, neutrons, and electrons.

Where are the subatomic particles located?

Protons and neutrons in the nucleus, electrons orbiting outside.

What defines an element?

The number of protons (atomic number, Z).

What is the charge and mass of an electron?

−1.602×10⁻¹⁹ C, 9.11×10⁻³¹ kg.

What is atomic number (Z)?

Number of protons in the nucleus.

What is atomic mass (A)?

Total number of protons + neutrons.

What are isotopes?

Atoms of the same element with different numbers of neutrons.

Example of isotopes?

Carbon-12 and Carbon-14.

What is atomic weight?

The weighted average of isotopic masses.

What is 1 amu equal to?

1/12 of the mass of carbon-12.

What is Avogadro’s number?

6.022 × 10²³ atoms or molecules per mole.

1 mole of iron weighs how much?

55.85 g.

What does the Bohr model describe?

Electrons orbit the nucleus in discrete energy levels.

What is meant by “quantized energy”?

Electrons can only have specific energy levels.

What’s the main idea of the wave-mechanical model?

Electrons behave as waves and exist in probability clouds (orbitals).

What does “n=3” tell you?

The electron is in the 3rd energy level (3s, 3p, or 3d).

What is the Pauli Exclusion Principle?

No two electrons can have the same 4 quantum numbers.

What is the Aufbau principle?

Fill the lowest energy levels first.

What is Hund’s rule?

When orbitals of identical energy (degenerate orbitals) are available, the ground state electron configuration has the maximum number of unpaired electrons with parallel spins

Write the configuration of sodium (Na).

1s² 2s² 2p⁶ 3s¹.

What are valence electrons?

Electrons in the outermost shell; they control bonding.

What is electronegativity?

The tendency of an atom to attract electrons.

Which direction does electronegativity increase?

Increases → left to right; decreases ↓ down a group.

What are electropositive elements?

Metals that easily lose electrons to form cations.

What are noble gases known for?

Full electron shells; chemically inert.

Why do atoms bond?

To lower energy and achieve stable electron configurations.

What two forces act between atoms?

Attractive (FA) and repulsive (FR) forces.

What is equilibrium spacing (r₀)?

The distance where FA + FR = 0.

What is bonding energy (E₀)?

Energy required to separate two bonded atoms.

How do ionic bonds form?

Electron transfer between metal and nonmetal.

Are ionic bonds directional?

No (non-directional).

Properties of ionic bonds?

Hard, brittle, high melting point, poor conductor.

How do covalent bonds form?

Atoms share electrons.

Are covalent bonds directional?

Yes.

Example of covalent bonding?

H₂, CH₄, Si, Diamond.

Common properties?

Strong, often insulators or semiconductors.

How does metallic bonding work?

Positive ion cores surrounded by a “sea of electrons”.

Are metallic bonds directional?

No.

Properties of metallic bonds?

Conductive, ductile, variable strength.

What are secondary bonds?

Weak attractions between molecules or atoms.

List the three types of secondary bonds.

van der Waals, dipole-dipole, hydrogen bonds.

What causes van der Waals bonds?

Temporary dipoles due to uneven electron movement.

What is a hydrogen bond?

Attraction between hydrogen and F, O, or N (very strong dipole).

Example of hydrogen bonding?

Between water molecules (H₂O).

Are most materials purely ionic, covalent, or metallic?

No, most have a mix of bonding types.

Example of mixed bonding?

SiC (mostly covalent, partially ionic).

Which type of bonding usually leads to high stiffness?

Strong primary bonds (large E₀).

What type of bond is found in NaCl?

Ionic.

What type of bond is found in copper?

Metallic.

What type of bond is found in diamond?

Covalent.

What kind of bonding holds water molecules together?

Hydrogen bonding.