Atoms, Molecules and Water Essential Building Blocks for Living Organisms

Comparison of Terms Element Substance that cannot be broken down to another substance with different properties Atom Smallest unit that has characteristic properties of the element Molecule Two or more atoms joined by chemical bonds

Composition of an Atom NucleusNucleus Proton = positively charged particle (+) Proton = positively charged particle (+) Neutron = uncharged particle (n or +) Neutron = uncharged particle (n or +) Number of protons + Number of neutrons = Atomic mass Number of protons = Atomic number Electrons = negatively charged particlesElectrons = negatively charged particles Number of electrons = Number of protons Number of electrons = Number of protons Each electron circles the nucleus in an orbit representing a specific energy level. C 12 6

Atomic Models Hydrogen (H) Helium (He) Nucleus Electron Shell

Different Kinds of Atoms Helium Max 2e - Carbon +7p + +4p + +2p + Innermost electron shell +4e - +4n ± +2n ± +2e - Oxygen Max 8e - +7e - +8n ± Phosphorus +5p + +5e - +4n ± Calcium 2e- 2n 2p+ 6e- 6n 6p+ 8e- 8n 8p+ 15e- 16n 15p+ 20e- 20n 20p+

Applying Your Knowledge MagnesiumChlorine Atomic Number 1217 Atomic Mass 2435 Number of Protons Number of Neutrons Number of Electrons

Electron Energy Levels Energy Level Capacity for Electrons In forming molecules, atoms combine to fill their outer energy levels.

Applying Your Knowledge MagnesiumChlorine Total Number of Electrons 1217 Number of Electrons in First Electron Shell Number Electrons in Second Electron Shell Number of Electrons In Third Electron Shell

Chemical Bonds Forces holding atoms together BondCharacteristics Ionic One atom loses an electron, another gains an electron Covalent Atoms share electrons Polar Covalent Atoms share electrons unequally Hydrogen Covalently-bound hydrogen is attracted to another atom

± + – ± + ±+ ± +± + ± + ± + ± + – – –– – – ± + – – – ± + – ± + ±+ ± +± + ± + ± + ± + – – –– – – ± + – – – – – – – – – – Ionic Bonding in NaCl ± + – ± + ±+ ± +± + ± + ± + ± + – – –– – – ± + – – –– Sodium #e=2+8+1=#p ± + – ± + ±+ ± +± + ± + ± + ± + – – –– – – ± + – – – ––– – – – – Chlorine #e=2+8+7=#p – – Sodium ion #e=#p-1 Chlorine ion #e=#p+1 – Electron Completely Transferred Negative charge Positive charge

Ionic Bonding in NaCl Cl - Na + Opposites attract.Opposites attract. Sodiums nestle between chlorines.Sodiums nestle between chlorines. Perfectly cubical crystals form.Perfectly cubical crystals form. Cl - Na +

Covalent Bonding Oxygen Atom Oxygen Molecule (O 2 ) Oxygen Molecule (O 2 )

In Water, Polar Covalent Bonds Join Oxygen and Hydrogen

Hydrogen Bonds Join Water Molecules O O H H H H – – + + Hydrogen Bonds Water molecules carry slight charges Electrons favor O over H Hydrogen bonds form between O of one water molecule and H of another

Due to hydrogen bonding, water shows Surface tension: concentration of hydrogen bonds at air-water interface Cohesion: water molecules associate with each otherCohesion: water molecules associate with each other

Due to hydrogen bonding, water shows Capillary Action: movement of water through a tube by cohesion and adhesion Adhesion: water molecules associate with other molecules or surfaces

Due to hydrogen bonding, water shows Imbibition: movement of water into wood or gelatin by capillary action

Due to hydrogen bonding, water resists temperature change Water has high values for Specific Heat: heat needed to change temperature Heat of Vaporization: heat needed to convert liquid to gas

Due to hydrogen bonding, density decreases upon freezing Ice floats!

Water as a Solvent Substances that dissolve in water = hydrophilicSubstances that dissolve in water = hydrophilic –Polar –Ionic Substances that are insoluble in water = hydrophobicSubstances that are insoluble in water = hydrophobic –Non-polar

NaCl Dissolves in Water Ionic bonds of NaCl give +/- charges Water has partial +/- charges O tends to join with Na + H tends to join with Cl -

Dissociation + WaterWater– Hydroxide ion + Hydrogen ion A few water molecules naturally dissociate into ions Hydroxide ion is negative and basic Hydroxide ion is negative and basic Hydroxide Hydroxide ion ion is negative and basic Hydrogen ion is positive and acidic Hydrogen ion is positive and acidic Hydrogen Hydrogen ion ion is positive and acidic

The pH Scale Neutral pH + = pOH – Increasingly Acidic pH + > pOH – Increasingly Basic pH + < pOH – Lemon Juice Lime Juice Stomach Acid Beer Coffee Urine Water Blood Sea Water Baking Soda Bleach Ammonia Oven Cleaner

Applying Your Knowledge What would be the chemical formula if magnesium and chlorine united to form a molecule? (Mg=magnesium; Cl=chlorine)What would be the chemical formula if magnesium and chlorine united to form a molecule? (Mg=magnesium; Cl=chlorine) Which electrons from each atom are involved in forming the bond(s)?Which electrons from each atom are involved in forming the bond(s)?