Atoms as Building Blocks Quiz

Atoms as Building Blocks

• Atoms are the fundamental units of matter.
• Elements are composed of only one type of atom.
• An atom's nucleus contains protons (positive charge) and neutrons (neutral charge).
• The electron cloud surrounding the nucleus contains electrons (negative charge) in distinct energy levels.

Inside the Nucleus: Protons & Neutrons

• The atomic number represents the number of protons and electrons, defining the element.
• The atomic mass is the sum of protons and neutrons.

Isotopes: Variations of an Element

• Isotopes of an element possess the same number of protons but different numbers of neutrons.
• The mass number is the total number of protons and neutrons.
• To find the number of neutrons, subtract the atomic number from the mass number.

The Valence Shell: Where Reactions Happen

• The valence shell is the outermost energy level in an atom.
• Valence electrons are the electrons in the valence shell and play a significant role in chemical bonding.

The Octet Rule: Stability in Bonding

• Atoms tend to gain, lose, or share electrons to achieve a stable electron configuration like that of a noble gas, typically with eight valence electrons.
• This tendency explains why atoms form chemical bonds.

Electronegativity: Pulling Power

• Electronegativity is a measure of an atom's ability to attract electrons towards itself.
• Electronegativity increases moving across the periodic table from left to right and decreases down the periodic table.

Chemical Bonds: Holding Atoms Together

• Ionic bonds result from the transfer of electrons between atoms, resulting in the formation of ions.
• Covalent bonds form when atoms share electrons.

Molecular Orbitals: The Region of Electron Sharing

• Molecular orbitals (MOs) represent regions in space where electron pairs are likely to be found in a molecule.
• Bonding MOs occur when atomic orbitals with the same phase overlap, reinforcing the bond.
• Antibonding MOs occur when atomic orbitals with opposite phases overlap, weakening the bond.

Hybridization: Mixing Atomic Orbitals

• Hybridization involves the mixing of atomic orbitals to create new hybrid orbitals that are spatially disposed to account for molecular geometry.
• For instance, in methane (CH4), the carbon atom undergoes sp3 hybridization, forming four equivalent hybrid orbitals that bond to four hydrogen atoms, resulting in a tetrahedral geometry.

Pi (π) Bonds: The Second Layer of Bonding

• In addition to sigma (σ) bonds, which result from the head-on overlap of atomic orbitals, molecules can have pi (π) bonds formed by the sideways overlap of p orbitals.
• π bonds are weaker than σ bonds.

Organic Structures: Depicting Molecules

• Organic structures can be represented in different formats, including line-angle formulas, condensed structures, and skeletal structures.

Geometry: How Molecules Look in 3D

• The geometry of molecules is influenced by the arrangement of electron pairs around the central atom.
• The Valence Shell Electron Pair Repulsion (VSEPR) theory predicts molecular geometry based on the repulsion between electron pairs.

Rotation: Freedom and Restriction

• Atoms connected by single (σ) bonds rotate freely due to low energy barriers for rotation.
• Double bonds, however, have a higher energy barrier for rotation due to the presence of π bonds, making rotation more difficult.

Isomers: Molecules with the Same Formula, Different Arrangements

• Stereoisomers are molecules with the same connectivity but different spatial arrangements of atoms.
• Cis-trans isomers are a type of stereoisomer that arise from restricted rotation in molecules with double bonds.

Bond Lengths: The Role of S & P Character

• The s character of a bond increases bond strength and decreases bond length because s orbitals are more spherical and closer to the nucleus.
• The p character of a bond decreases bond strength and increases bond length because p orbitals are more elongated and farther from the nucleus.