Post on 04-Jan-2016
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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