ap bio 2a2b typee!

chemical bonds & reactions

1. electronegativity

electronegativity: how strongly an atom attracts shared electrons.

• higher electronegativity = stronger pull on electrons

• oxygen has a high electronegativity

• when atoms have different electronegativities, electrons may be shared unequally.

remember:

electronegativity = electron-pulling power

2. covalent bonds

covalent bond: atoms share electrons.

nonpolar covalent

• electrons are shared equally

• usually between atoms with similar electronegativities

• example: o₂

polar covalent

• electrons are shared unequally

• one atom pulls the electrons closer

• creates partial charges: δ+ and δ−

remember:

covalent = share

3. ionic bonds

ionic bond: electrons are transferred from one atom to another.

this creates ions:

• losing electrons → positive ion (+)

• gaining electrons → negative ion (−)

• opposite charges attract → ionic bond

remember:

ionic = transfer

4. bond strength

from strongest → weakest:

ionic bonds → covalent bonds → hydrogen bonds → van der waals interactions

⚠ memorize this order for the quiz.

5. hydrogen bonds

a hydrogen bond is a weak attraction between a partially positive hydrogen and a partially negative atom, usually oxygen or nitrogen.

in water:

hδ+ ←→ oδ−

hydrogen bonds occur between molecules, not within a water molecule.

6. van der waals interactions

very weak attractions caused by temporary uneven distributions of electrons.

individually weak, but many together can create significant attraction.

example: geckos sticking to walls.

⚗ chemical reactions

7. reactants vs. products

reactants: substances you start with.

products: substances made by the reaction.

general format:

reactants → products

8. photosynthesis equation

memorize this:

6co₂ + 6h₂o → c₆h₁₂o₆ + 6o₂

reactants:

• carbon dioxide (co₂)

• water (h₂o)

products:

• glucose (c₆h₁₂o₆)

• oxygen (o₂)

9. chemical equilibrium

chemical equilibrium: when the forward and reverse reactions occur at the same rate.

this means the amounts of reactants and products remain relatively constant.

⚠ equilibrium does not mean the reaction stops.

💧 2b — water

10. why water is polar

water (h₂o) has:

• 1 oxygen

• 2 hydrogens

oxygen attracts electrons more strongly than hydrogen.

therefore:

oxygen → δ−
hydrogens → δ+

this uneven charge distribution makes water polar.

remember:

oxygen pulls → oxygen becomes slightly negative

🔗 hydrogen bonding in water

11. how water molecules hydrogen bond

the δ+ hydrogen of one water molecule is attracted to the δ− oxygen of another.

the dotted line between water molecules represents the hydrogen bond.

one water molecule can form:

up to 4 hydrogen bonds

💧 properties of water

12. cohesion vs. adhesion

cohesion

water molecules stick to other water molecules.

cohesion = same

adhesion

water sticks to different substances.

adhesion = different

13. water droplets

water forming beads/droplets demonstrates cohesion.

hydrogen bonding causes water molecules to stick together.

14. surface tension

surface tension: the resistance of water's surface to being broken.

caused by cohesion/hydrogen bonding.

example:

water striders can walk on water because of surface tension.

🌡 specific heat

15. specific heat

specific heat: the amount of energy needed to change a substance's temperature.

water has a high specific heat.

that means:

➡ it takes a lot of energy to heat water
➡ it takes a lot of energy to cool water
➡ water changes temperature relatively slowly

water has a higher specific heat than iron.

16. why water has high specific heat

hydrogen bonds absorb energy.

before water molecules can move significantly faster, energy must disrupt some of these hydrogen bonds.

therefore, water requires more energy to increase its temperature.

17. why high specific heat matters to life

water helps moderate temperature changes.

this helps:

• organisms maintain stable temperatures

• aquatic environments avoid extreme temperature changes

• ecosystems remain more stable

🧊 freezing & ice

18. why does ice float?

ice is less dense than liquid water.

when water freezes, hydrogen bonds hold the molecules in a more spread-out structure.

therefore:

ice = less dense → floats

19. why is this important?

floating ice forms an insulating layer on top of lakes and ponds.

this prevents the entire body of water from freezing solid, allowing organisms to survive underneath.

🧪 water as a solvent

20. solvent

solvent: the substance that does the dissolving.

21. solute

solute: the substance being dissolved.

22. solution

solution: a uniform mixture of a solute and solvent.

example: sugar water

water = solvent
sugar = solute
sugar water = solution

23. why is water a good solvent?

water is polar, so it can attract and surround ions and other polar molecules.

remember:

polar water dissolves polar/charged substances well.

🫧 hydrophilic vs. hydrophobic

24. hydrophilic

hydrophilic = water-loving

• interacts well with water

• often polar or charged

• tends to dissolve in water

25. hydrophobic

hydrophobic = water-fearing

• does not mix well with water

• often nonpolar

• does not form hydrogen bonds effectively with water

example:

oil is hydrophobic, so it separates from water.

🧴 why oil doesn't dissolve in water

oil is nonpolar.

water is polar.

because oil cannot form the same favorable interactions with water, the molecules separate.

remember:

"like dissolves like"

polar → polar
nonpolar → nonpolar

🧪 acids & bases

26. h⁺

h⁺ = hydrogen ion

important:

more h⁺ → more acidic → lower ph

27. acid

acid = increases h⁺

28. base

base = decreases h⁺

or increases oh⁻.

📊 ph scale

memorize:

0 ————— 7 ————— 14
acidic | neutral | basic

• 0–6 = acid

• 7 = neutral

• 8–14 = base

examples:

🧪 buffers

29. what is a buffer?

a buffer resists changes in ph.

it can:

• absorb excess h⁺

• release h⁺ when needed

this keeps ph relatively stable.

30. exercise & blood ph

exercise increases co₂ production.

more co₂ can lead to more h⁺, making blood more acidic.

the body's buffer system helps absorb excess h⁺ and minimize changes in blood ph.

basic idea:

exercise → ↑ co₂ → ↑ h⁺ → ↓ ph

buffer → limits the ph change

⭐ must-know comparisons

covalent vs. ionic

covalent: shares electrons
ionic: transfers electrons

polar vs. nonpolar covalent

polar: unequal sharing
nonpolar: equal sharing

cohesion vs. adhesion

cohesion: same molecules
adhesion: different molecules

hydrophilic vs. hydrophobic

hydrophilic: interacts with water
hydrophobic: avoids water

acid vs. base

acid: ↑ h⁺
base: ↓ h⁺

solvent vs. solute

solvent: does the dissolving
solute: gets dissolved