Water as a molecule

Water as a molecule

• Water has a polar covalent bond

• The electrons are shared unevenly

• Oxygen is stronger, so it pulls the electrons to itself

Water as a molecule

• Water is a polar molecule• One part is more negative,

and one part is more positive

Water as a molecule

• The polar parts of water will connect, giving water special properties

**You will see these properties in lab**

Vocabulary

• POLAR – a molecule that has an uneven distribution of electrons

• POLAR - una molécula que tiene una distribución desigual de los electrones

• POLAR - 的分子，具有電子的不均勻分佈

Vocabulary

• Cohesion – when similar things stick to each other (ex: water molecule to other water molecules to form drops)

• Adhesion – When different things stick to each other (ex: water sticks to grass)

Lab part 1

• Talk in lab group – record in notebook– What did you observe? – Explain why you saw what you did

• Share out – whole group– Many drops could fit on the penny than we

predicted– This happened because of cohesion. The water

molecules stuck to each other to allow more water to fit.

Lab part 2

• Talk in lab group – record in notebook– What did you observe? – Explain why you saw what you did

• Share out – whole group– The paper clip could float on water. – This happened because of cohesion. The water

molecules stuck to each other to allow more water to fit.

Lab part 3

• Question: How do different chemicals affect the surface tension of water?

• Safety!! – Wear goggles when handling chemicals

• Make sure to get your procedure approved BEFORE conducting your experiment

• Use a new pipette for each solution to avoid contamination (mixing the chemicals by accident)

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Vocabulary

• Nonpolar - a compound where electrons are shared equally. Areas of the compound are neutral.

• Hydrophobic – “scared of water” a substance that does not dissolve in water. Nonpolar substances are hydrophobic.

• Hydrophilic – “Water loving” a substance that will dissolve in water. All polar substances are hydrophilic

Detergents (Soap)

• Micelle– Forms when hydrophobic ends clump together

• Detergent molecules have a polar end and a non polar end

Detergents• Amphiphilic – has a polar and a nonpolar end.

Detergents have a hydrophobic end and a hydrophilic end.

The polar end will dissolve in water The nonpolar end will dissolve in oil

Properties of water

• Cohesion – water sticks together• Resistance to temperature change – needs a

lot of energy to raise temperature• Density – solid ice floats in liquid water• Universal Solvent – can dissolve almost

anything

How soap dissolves oil

How soap dissolves oil

• Green head=hydrophillic, polar, dissolves in water

• Yellow tail – hydrophobic, nonpolar, dissolves oil

• LIKE DISSOLVES LIKE

Quiz next week: Properties of water

• 4 properties from reading # 3.5• Solubility• Polar• Non-polar• Amphipathic• Experimental design– Controlling an experiment

As you read…

Create definitions for the following terms• Solubility• Solute• Solvent• Homogeneous• Solution• Mixture

Vocab

• Mixture - a system where 2 or more things are combined, but not chemically

• Solution – when 2 or more things are combined evenly

• Solubility – The amount of solute that can be dissolved by a solvent

Vocab

• Homogeneous mixture – a mixture that is evenly mixed. (ex. CO2 bubbles in soda) AKA a solution

• Heterogeneous mixture – a mixture that is unevenly mixed. (ex. Sand in water)

Vocab

• Solvent – the substance that dissolves the solute (often, it is water)

• Solute - the substance that is dissolved