3.1 Chemical elements & water

IB Biology

Chemistry RecapElement - pure substance, made of one kind of atom, unique chemical and physical properties

Molecules - two or more atoms chemically combined through a covalent bond

Ion - an atom or molecule with an electric charge

ElementsMost common elements in living things

Carbon (C)

Hydrogen (H)

Oxygen (O)

Nitrogen (N)

C, H, N, O found in proteins and nucleic acid (DNA)

C, H, O found in carbohydrates and lipids

Elements found in small amounts

Sulfur (S)Needed for some proteins in all organismsNeeded for some proteins in all organismsForm disulphide bondsForm disulphide bonds

Phosphorus (P)In DNA and ATP

Calcium (Ca/Ca+)Bone structure, muscle contraction, cell division, regulation of cell processes

Iron (Fe)Aerobic cellular respiration

Sodium (Na/Na+)Nerve signals (animals), controls amount of water in cytoplasm

Bonding

Ionic BondIonic Bond - Gain / loss of electrons - Gain / loss of electrons

Covalent BondCovalent Bond - Sharing electrons - Sharing electrons

Polar Covalent BondsCovalent bond - bond Covalent bond - bond within moleculewithin molecule

Sometimes atoms in a Sometimes atoms in a covalent bond do not covalent bond do not share electrons share electrons equally..

The result is a bond The result is a bond with a with a slightly positive end and a slightly negative end as seen in as seen in water molecules.water molecules.

Hydrogen Bonding in WaterIntermolecular force

Since water is Since water is polar, the , the positive ends attract the positive ends attract the negative ends.negative ends.

This attraction creates This attraction creates hydrogen bonds.

Hydrogen bonds are Hydrogen bonds are weak individually, but individually, but together lead to the together lead to the unique properties of unique properties of waterwater

Water

H2O - two hydrogen atoms, one oxygen atoms

Molecule formed by polar covalent bond

Unequal sharing of electrons

Forms a charge distribution

Partial positive and partial negative

Hydrogen bond gives water unique properties

Properties of Water

CohesionWater molecules stick to each other due to Water molecules stick to each other due to hydrogen bonds hydrogen bonds betweenbetween them them

Surface tension

Cohesion Activity

Obtain a 1 dirham coinUse an eyedropper to place water onto coin, 1 drop at a timeRecord # of drops and qualitative observationRepeat with a small amount of dish soap on coinDiscuss results

Cohesion - Water used as a transport medium

Many substances can be dissolved and Many substances can be dissolved and therefore carried in watertherefore carried in water

The The cohesion of water lets it be pulled of water lets it be pulled to a great height in plants, to a great height in plants, transporting dissolved substances

Water can also Water can also transport heat due to its due to its high heat capacity (blood carries from high heat capacity (blood carries from one body part to another, etc.)one body part to another, etc.)

Properties of WaterVersatile solvent

Because water has areas of Because water has areas of partial positive and negative partial positive and negative charge, it can charge, it can dissolve many many substances that are substances that are polar, positively charged, or negatively charged

Water does NOT dissolve non- non-polar, uncharged substances polar, uncharged substances (lipids / fats / oils)(lipids / fats / oils)

Medium for most Medium for most chemical reactions in living organisms in living organisms

Solvent: Water as a medium for metabolic reactions

Solvent: most reactions of life happen most reactions of life happen with the substances dissolved in water with the substances dissolved in water (cytoplasm is mostly water)(cytoplasm is mostly water)

Ex. Oxygen from the air must dissolve into Ex. Oxygen from the air must dissolve into the water on the inside of the lungsthe water on the inside of the lungs

State: the : the liquid state allows substances state allows substances to stay in the liquid but to stay in the liquid but move around enough to come in contact and reactenough to come in contact and react

Excellent for metabolic reactionsExcellent for metabolic reactions

Properties of WaterThermal properties

Heat capacity Heat capacity (high specific heat): (high specific heat): large amounts of large amounts of energy are needed to raise the temperature of waterare needed to raise the temperature of water

State changes State changes (high heat of vaporization): (high heat of vaporization): water boils water boils at a high temperature and has a at a high temperature and has a large temperature range as a liquid as a liquid

Evaporative coolingEvaporative cooling (high heat of vaporization): (high heat of vaporization): energy energy taken to taken to break hydrogen bonds and free water and free water molecules as they evaporate, cools remaining water molecules as they evaporate, cools remaining water

Thermal properties: Water as a Thermal properties: Water as a coolantcoolant

Evaporative cooling: Terrestrial organisms may : Terrestrial organisms may sweat or pant to remove excess heat to remove excess heat

Heat capacity: Water organisms may transfer heat to : Water organisms may transfer heat to the environment without raising the water the environment without raising the water temperature by muchtemperature by much

Video

Properties of water

http://www.sumanasinc.com/webcontent/animations/content/propertiesofwater/water.html

Homework

Pg 42 Thinking about science