Lecture 1 Flashcards
Introduction to Bonding and Intermolecular Force
What is an atom?
An atom is the smallest unit of matter that retains the chemical properties of an element.
What is an element?
An element is a pure substance made up of only one type of atom and cannot be broken down by physical or chemical means.
What is a compound?
A compound is a pure substance composed of two or more elements that are chemically combined.
What is a molecule?
A molecule is two or more atoms chemically bonded together, which can be the same or different types of atoms.
Know what each represents chemically.
Atoms make up elements, molecules are bonded atoms, and compounds are molecules with different elements.
What are the subatomic particles?
Protons (positive, nucleus, 1 amu), Neutrons (neutral, nucleus, 1 amu), Electrons (negative, orbitals, negligible mass).
Which subatomic particle participates in chemical bonding?
Electrons, specifically valence electrons, participate in chemical bonding to achieve an octet.
Where are electrons usually found in an atom?
Electrons are arranged in electron shells or energy levels (think of different floors in a mall). Within those shells electrons occupy specific orbitals (s, p, d, f) which are like stores or rooms on each floor where electrons are most likely to be found
What are valence electrons?
Valence electrons are the electrons that occupy the outermost shell.
What is an octet?
An octet is when an atom reaches stability with a full outer shell of 8 electrons, with exceptions like hydrogen.
Be able to use the concept of an octet to determine the number of electrons needed for bonding.
- Determine the number of electrons in the atom (atomic number). 2. Fill shells based on 2(n)^2 rule.
What is the difference between an ionic bond and a covalent bond?
Ionic bonds involve electron transfer (metal + nonmetal), covalent bonds involve electron sharing (nonmetals).
How are covalent bonds represented in a Lewis dot structure?
Covalent bonds are represented as single (–), double (=), or triple (≡) straight lines.
How are lone pairs of electrons represented in a Lewis dot structure?
Lone pairs are represented as dots around an atom, showing non-bonded electrons.
How many electrons are in a single bond?
2 electrons (1 shared pair).
How many electrons are in a double bond?
4 electrons (2 shared pairs).
How many electrons are in a triple bond?
6 electrons (3 shared pairs).
How can one determine if a covalent bond is polar or nonpolar?
By checking electronegativity differences: polar bonds have partial charges, nonpolar bonds share electrons equally.
Know the various symbols used to determine a dipole.
Dipole symbols: δ+ (partial positive), δ- (partial negative), and an arrow pointing to the more electronegative element.
How are electrons distributed in a nonpolar vs. polar covalent bond?
Polar: Unequal sharing, dipole formed. Nonpolar: Equal sharing, no dipole.
What are bonding vs. nonbonding (intermolecular) forces?
Bonding forces occur within molecules (strong), nonbonding forces occur between molecules (weaker).
What are the three types of intermolecular forces?
Hydrogen bonding, dipole-dipole interactions, and London dispersion forces.
What are the conditions for London dispersion forces?
They occur in all molecules but dominate in nonpolar ones; stronger in larger molecules with more electrons. London dispersion forces happen due to random electron movement. When two molecules are next to each other, one molecule randomly develops a temporary dipole due to the movement of electrons. Thid temporary dipole induces a dipole in their neighboring molecule. These molecule are then weakly attracted to each other because of these temporary charges.
What are the conditions for dipole-dipole forces?
Dipole-dipole interactions occur between polar molecules with permanent partial charges.
What are the conditions for hydrogen bonding?
An H atom must be covalently bonded to N, O, or F in one molecule and interact with a lone pair on another N, O, or F in a different molecule.
How do you identify an H-bond donor vs. acceptor?
The molecule supplying H is the donor; the molecule with the lone pair is the acceptor.
Do all polar molecules participate in hydrogen bonding?
No, only molecules where H is bonded to N, O, or F can hydrogen bond.
Can nonpolar molecules mix with water?
No, because water is polar and nonpolar molecules are hydrophobic, causing them to separate.
Why is water polar and not linear?
Water has an unequal sharing of electrons, creating dipole interactions; a linear shape would cancel out charges.
Why can’t dimethyl ether molecules hydrogen bond?
They lack N, O, or F with a lone pair of electrons.
How do two molecules of dimethyl ether interact?
Dipole-dipole interactions.
Why are lone pairs important?
They impact molecular shape, polarity, and interactions. Atoms with lone pairs are often polar and can participate in hydrogen bonding.
Why don’t nonpolar molecules dissolve in water?
Water forms strong hydrogen bonds with itself and cannot form strong interactions with nonpolar molecules, causing them to be excluded.
If London dispersion forces are weak, why don’t nonpolar molecules dissolve in water?
Dissolving requires breaking old forces and forming strong new ones. Water cannot form strong enough bonds with nonpolar molecules.
What happens when a nonpolar molecule enters water?
Water molecules rearrange themselves to form a ‘cage’ around the nonpolar molecule, leading to phase separation (hydrophobic effect).
