Chemistry Test --- Nonpolar, Polar, and IMF

what are London Dispersion Forces?

• weak intermolecular forces that happen because electrons are always moving

• as they move, they create temporary and uneven charges in a molecule that can induce a dipole in another molecule

• this causes small attractions between two molecules

what is dipole?

molecule with two ends with opposite charges

what factors affect the amount of LDF?

• number of electrons (more electrons = stronger LDF)

• polarizable (larger atoms = more polarizable = stronger LDF)

• surface area/shap (bigger/longer molecules = stronger LDF)

• distance between molecules (closer = stronger LDF)

what substance will have the highest boiling point from alkanes? why?

• ones with the most carbon atoms

• as it gets bigger, it has more electrons which makes it more polarizable making LDF stronger

• when LDF is stronger, more energy is needed to separate the molecules

• longer carbon chain = higher boiling point

what is the difference between ionic and covalent physical properties?

ionic

• electrons transferred

• nonmetals and metals

• ions

• high melting/boiling points

• conduct electricity when dissolved in water

• soluble

covalent

• electrons shared

• nonmetals

• molecules

• lower melting/boiling point

• not as conducive

how are polar and nonpolar covalent compounds different?

polar

• unevenly shared

• partial charges, dipole

• happens when atoms have different electronegativity

nonpolar

• evenly shared

• no partial charges or dipole

• same or very similar electronegativity

what is the difference between smaller and larger nonpolar/polar covalent compounds?

smaller nonpolar and polar covalent compounds

• less electrons, so less polarizable

• weaker LDF

• lower boiling and melting points

• usually gases

larger nonpolar and polar covalent compounds

• more electrons, so more polarizable

• stronger LDF

• higher boiling and melting points

• liquids or solids at room temperature

what is vaporization? what affects it?

• liquid —> gas

affected by:

• temperature (higher temperature = faster vaporization because particles have enough energy to escape)

• surface area (more surface area = faster vaporization because more molecules are expose to air)

• intermolecular forces (weaker forces = faster vaporization because it is harder for molecules to pull away)

what are the different types of intermolecular forces from weakest to strongest? explain.

1. London Dispersion Forces: weakest; in all molecules (esp. nonpolar); temporary dipoles from moving electrons; strength increases with more electrons/larger molecules

2. Dipole-Dipole Forces: polar molecules; positive end attracts negative end of another

3. Hydrogen Bonding: when hydrogen (H) is bonded to nitrogen (N), oxygen (O), or fluorine (F)

4. Ion-Dipole Force: strongest; ion and polar molecule

what is vapor pressure? what substances have a greater vapor pressure?

• vapor pressure: how easily liquid turns into a gas

• volatile substances, small molecules, and weak IMF molecules have high vapor pressures

what substances have greater boiling/melting point?

molecules withs strong IMF, large molecules, or molecules that can form hydrogen bonds

practice identifying polar and nonpolar substances and chemical bonds.

ask ChatGPT

know the 3D models for the Lewis Dot structures.

memorize

what does it mean for a substance to be symmetrical or asymmetrical?

• symmetrical: shape is even and all parts are balanced (usually nonpolar)

• asymmetrical: shape is uneven and there is dipoles (usually polar)

identify if these substances are nonpolar or polar: oil, gasoline, isopropyl alcohol

• oil: nonpolar

• gasoline: nonpolar

• isopropyl alcohol: polar (has OH group)

what are intermolecular forces? why are they important?

• force of attraction between molecules

important because it determines:

• boiling and melting points (stronger IMF = higher boiling/melting point)

• vapor pressure (weaker IMF = higher vapor pressure)

• solubility (like dissolves like)

• state of matter (stronger IMF = solid/liquid ; weaker IMF = gas)

how does soap work?

have both polar and nonpolar ends allowing it to mix with polar water and wash off nonpolar substances (like oil)

why do certain substances, like sugar, dissolve in water? why is it not conducive?

• sugar is made of polar molecules and water is polar, so it dissolves

• sugar does not form ions in water, it just disperses

• for electricity to be formed by dissolving something in water, it needs to form ions in water (like salt)

when can a molecule form hydrogen bonds?

when it is directly boned to O, N, or F

what is lattice energy? what affects it?

• energy released when 1 mole of an ionic solid forms its ions in the gas phase (how strongly ions are held together in solid)

factors that affect lattice energy:

• charge of ions (higher charged = stronger attraction = higher lattice energy)

• size of ions (smaller ions = closer together = stronger attraction = higher lattice energy)

ionic compounds with the highest lattice energy is usually one with ___ ___ and ___ ___ ___.

small ions; highly charged ions

practice putting lattice energy ionic compounds in order from most to least.

practice

practice ionic and covalent compounds in 2D Lewis structures.

practice

what is an electrolyte? what substances produce them?

• substance that produces ions in solutions and can conduct electricity

• ionic compounds can make electrolytes EXCEPT sugar and ethanol

practice identifying IMF in compounds.

practice

what is adhesion? give an example.

• attraction between molecules of different substances

• example: water molecules sticking to glass

what is cohesion? give an example.

• attraction between molecules of same substance

• water molecules sticking to each other

practice ranking ionic compounds and polar/nonpolar covalent compounds in order of boiling/melting point.

practice

why do certain compounds have higher melting/boiling points?

• stronger IMF = higher melting/boiling point

• size of molecule/# of electrons (larger molecule = more electron = stronger LDF = higher melting/boiling point)

• straight chains with more surface area = higher melting/boiling point

memorize all the alkane from methane to decane. know the Lewis structures for them.

memorize

how does salt dissociates in water?

• positive sodium connects to negative oxygen

• negative chlorine connects to positive hydrogen

know how to name ionic and covalent compounds.

practice

what is specific heat?

amount of energy needed to increase temperature of 1 gram of a substances to 1ºC

what are biomolecules?

organic compounds found in living things

what is the difference between intermolecular and intramolecular forces?

• intermolecular: holds molecules together

• intramolecular: holds atoms together in molecules

what are hydrocarbons? what is the difference between them?

• alkane: single bond

• alkene: 1 or more double bonds

• alkyne: 1 or more triple bonds

bigger hydrocarbons are what at room temperature? smaller hydrocarbons are what at room temperature?

• bigger: liquid

• smaller: gas

what are isomers?

compound with same formula and different structures