What is the chemical formula for water? Draw the structure of water. Write down all the types of...
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Transcript of What is the chemical formula for water? Draw the structure of water. Write down all the types of...
•What is the chemical formula for water?
Draw the structure of water.Write down all the types of bonding that you know of.
Surface Tension
Water ClingsHigh Surface Tension – water
molecules form hydrogen bonds with each other creating cohesion
A water strider can walk on the surface of a pond.
Capillary Action – water molecules from hydrogen bonds with other polar molecules creating adhesion
Capillary action causes water to creep up a narrow glass tube and paper.
Hydrogen Bonding in WaterHydrogen bonding causes water to absorb a
large amount of heat before
its temperature increases
appreciably and also causes
it to lose large amounts of
heat before its temperature
decreases significantly.
(Heat Capacity)
High heat capacity allows
organisms to maintain a
constant body temperature.
Hydrogen bonding causes
liquid water to absorb a large
amount of heat to become a
vapour. Many organisms
(including humans) dissipate body
heat by evaporation of water from
surfaces (skin-sweating; tongue-panting)
Chemical Context of Life
Matter (space & mass)
Element; compound The atom Atomic number (# of
protons); mass number (protons + neutrons)
Isotopes (different # of
neutrons); radioactive isotopes (nuclear decay)
Energy (ability to do work); energy levels (electron states of potential energy)
Covalent Bonding
Sharing pair of valence electrons
Number of electrons required to complete an atom’s valence shell determines how many bonds will form
Ex: Hydrogen & oxygen bonding in water; methane
Covalent bonding
Practice some examples of Covalent Bonding using Lewis structures.
What other properties do covalent bonds have?
Polar/nonpolar covalent bonds
Electronegativityattraction for electrons
Nonpolar covalent •electrons shared
equally •Ex: diatomic H and O
Polar covalent•one atom more electronegative than the other (charged)•Ex: water
Polar/nonpolar bondsRecall ►
Covalent bonds may be polar or nonpolar
Nonpolar covalent – electronegativity difference = 0
Polar covalent – electronegativity difference is greater than 0 but less than 1.7
Molecular polarity – dependant on both bond polarity and molecular shape
Symmetrical molecules whose bonds are all polar are nonpolar.
Asymmetrical molecules are nonpolar of all bonds are nonpolar, and they are polar if at least one bond is polar.
Ionic bonding
High electronegativity difference strips valence electrons away from another atom
Electron transfer creates ions (charged atoms)
Cation (positive ion); anion (negative ion)
Ex: Salts (sodium chloride)
Ionic bonds
Practice drawing ionic compounds using lewis structures.
What are some other properties of ionic bonds?
Hydrogen bonds
Hydrogen atom covalently bonded to one electronegative atom is also attracted to another electronegative atom (oxygen or nitrogen)
van der Waals interactions
Weak interactions between molecules or parts of molecules that are brought about by localized change fluctuations
Due to the fact that electrons are constantly in motion and at any given instant, ever-changing “hot spots” of negative or positive charge may develop
Water Polar~ opposite ends, opposite charges Cohesion~ H+ bonds holding molecules
together Adhesion~ H+ bonds holding molecules to
another substance Surface tension~ measurement of the
difficulty to break or stretch the surface of a liquid
Specific heat~ amount of heat absorbed or lost to change temperature by 1oC
Heat of vaporization~ quantity of heat required to convert 1g from liquid to gas states
Density……….
Density
Less dense as solid than liquid
Due to hydrogen bonding
Crystalline lattice keeps molecules at a distance
Acid/Base & pH
Dissociation of water into a hydrogen ion and a hydroxide ion
Acid: increases the hydrogen concentration of a solution
Base: reduces the hydrogen ion concentration of a solution
pH: “power of hydrogen” Buffers: substances that
minimize H+ and OH- concentrations (accepts or donates H+ ions)
a single, very small particle with a
negative charge that isfound in a “cloud” around the nucleus
ELECTRON (e-)
Please complete the following table
Protons Neutrons Electrons
Where are they found?
Mass
Charge (attitude)
Nucleus Nucleus Electron Cloud
Heavy Heavy Very Light
Positive Neutral Negative
The total mass of all of the subatomic particles
in an atom (but really # of protons and
neutrons)
ATOMIC MASS #(A)
the number of protons in an atom
(assuming the atom is neutral, # of p+ = # of e-)
ATOMIC NUMBER (Z)
To calculate the number of neutrons, subtract the atomic number (smaller)
from the atomic mass number (larger)
A – Z = # of neutrons
Ex: How many neutrons does Sodium have?
Mass # - Atomic # = #N°(You may need to round the atomic #)
23 - 11 = 12 N°Na11
22.99
Atoms of the same element that differ in
charge.(They have the same # of p+, but different # of e-)
ION
Positive Ions(cations)
Negative Ions(anions)
• Na+ (lost 1 e-)
• Ca2+ (lost 2 e-)
• Al3+ (lost 3 e-)
• Pb4+ (lost 4 e-)
• H+ (lost 1 e-)
• Cl- (gain 1 e-)
• O2- (gain 2 e-)
• P3- (gain 3 e-)
• S2- (gain 2 e-)
• OH- (gain 1 e-)
If an atom GAINS electrons, its overall charge
becomes more negative.If it LOSES electrons, its
charge becomes more positive
Atoms of the same element that differ in
mass.(They have the same # of p+, but different # of N°)
ISOTOPE
Isotopes are CHEMICALLY the SAME as atoms, but
DIFFER PHYSICALLY because they have different masses.