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BIOA01H3 (200)
Chapter 2

Chapter 2 Study Guide


Department
Biological Sciences
Course Code
BIOA01H3
Professor
Mark Fitzpatrick
Chapter
2

Page:
of 4
Chapter 2 The Chemistry of Life
Chemical Elements
-all matter is composed of atoms
-atom consists of a dense, positively charged nucleus & negatively charged electrons orbit
around the nucleus
-nucleus contains protons & neutrons
-atomic mass unit (amu) is mass of proton
-mass of electrons can be ignored because its mass is very low
-proton has positive electric charge, +1
-electron has negative charge equal to that of proton, -1
-neutron is neutral & has no charge
-when number of proton equals number of electron, atom is neutral
Element
-element is pure substance that contains only one kind of atom
-6 main elements found in organism: carbon, hydrogen, nitrogen, oxygen, phosphorus, sulfur
Protons
-atomic number is the number of proton
-mass number is the total number of proton & neutron in the nucleus
-atomic number is written at the lower left, mass number at the upper left
Neutrons
-isotope is element that has the same number of proton, but different number of neutron
-atomic mass/ atomic weight is the average mass of element based on the relative abundance of
various isotopes
-radioisotope is unstable & gives off energy in the form of alpha, beta or gamma radiation from
atomic nucleus
-can be used as tag and label to trace organism
-radioactive decay is the release of energy that transforms original atom
->can change number of protons, resulting in different elements
Electrons
-impossible to determine the exact location of electron at any given time
-can only estimate the volume of space electron is located in orbital
-1st electron shell contains 1 s-orbital, hold up to 2 electrons
-2nd electron shell contain 4 orbitals (1 s-orbital, 3 p-orbital), hold up to 8 electrons
-higher energy level means electron needs more energy to overcome the pull of positively
charged nucleus
-s-orbital (the lowest energy level) fills with electrons first
-valence (outermost electron shell) determines how atom behaves chemically
-atom is stable when valence shell reaches maximum number of electrons
-stable elements are helium neon, argon (noble gas)
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-reactive atom has unpaired electrons in valence shell
->become stable by gaining/ losing electrons
->atoms bond with other atom to form molecules
-Octet Rule is the tendency of having 8 electrons in valence shell to gain stability
How do Atoms Bond to Form Molecules?
-chemical bond-> the attractive force that causes 2 atoms to come together & form molecules
-covalent bond-> strong bond results from sharing of electrons
->when non-metal atoms share 1 or more pairs of electrons in valence shell e.g. H2, O2
->strong bond so a lot of energy is needed to break them
-ionic bond-> one atom gains electrons and the other atom loses electrons
-compound-> 2 or more elements bonded together in fixed ratio e.g. H2O, CO2
-molecular weight (molecular mass) -> sum of atomic weight of all atoms in the molecule
-bonding capacity-> the number of covalent bond/ pair of electron an atom can have
Multiple Covalent Bonds
-3Types of covalent bond
1) Single bond-> sharing of 1 pair of electrons e.g. H2
2) Double bond-> sharing of 2 pairs of electrons e.g. CH4
3) Triple bond-> sharing of 3 pairs of electrons e.g. N2
-2 atoms of the same element bond together results in equal sharing of electrons
-2 atoms of different element bond together can result in unequal sharing of electrons
->1 nucleus may have greater attractive force to pull the electrons closer to the nucleus than that
of another atom
-electronegativity-> attractive force that atomic nucleus exerts on electrons
-2 factors that determine electronegativity
1) Number of proton, more protons, greater attractive force
2) Distance between nucleus & electron, the closer they are, the greater force
-2 atoms that have similar electronegativity forms non-polar covalent bond e.g. CO2
-polar covalent bond-> electrons are drawn close to the atom that has greater electronegativity,
an unequal sharing of electron e.H2O
->in water, electrons are pulled toward oxygen atom, making it slightly negative (delta negative),
hydrogen is delta positive
-polar-> opposite charges at two end in the compound
Ionic Bonds Form by Electrical Attraction
-ionic bond-> complete transfer of 1/more electrons
-ions-> electrically charged particles when atoms lose or gain electrons
-2 types of ions
1) Cation is positively charged e.g. Na+
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2) Anion is negatively charged e.g. Cl-
-complex ions-> groups of covalently bonded atom that carry electrical charge e.g. NH4+, PO43-
-electrical attraction between ions of opposite charges
-ionic bond in solid state is strong & stable because the distance between atoms are closer
-weaker attraction force in liquid & gas
-ions interact with polar molecules, where the negatively charged ions attract with the delta
positive particle, vice versa for positively charged ions
-hydrogen bond-> when the delta negative oxygen attract delta positive hydrogen of another
compound
-hydrogen bond is weaker than ionic bond because it is only formed by partial charges
Hydrogen Bond
-hydrophilic (water loving) -> polar molecules interact with water
-hydrophobic (water hating) -> nonpolar molecules interact with each other
->can still form weak interaction with water, known as van der Waal force (weak force)
->larger nonpolar molecules can have larger van der Waal force, which may accumulate to form
a stronger force
Chemical Reaction
-chemical reaction-> reactants interact together to form product
-matter is neither created nor destroyed in a reaction
->mole of reactant = mole of product
-energy is changed from one form to another
->potential chemical energy into thermal energy in combustion reaction
-some reaction requires energy (endothermic), some release energy (exothermic)
-complete reaction-> all reactants are converted to product
-incomplete reaction-> not all reactants are converted to product
-intermediate step is extra small reactions that achieve the overall chemical reaction e.g.
breakdown of glucose
-> start with the same reactant and product the same reactant
->energy is not released all at once, but partially released in each step, otherwise cell will be
exploded
Properties of Water
-water is polar & can form hydrogen bond
-in ice, water molecules are held by hydrogen bond
->molecules are not tightly packed as they are in liquid
->solid water is less dense than liquid water, so ice floats on surface of water
->acts as an insulating layer on top on pond, protects animals underneath
-freezing releases energy, melting requires energy
-specific heat-> amount of heat energy required to raise 1 gram of that substance by 1ºC
-water has high specific heat because it takes great amount of energy to raise its temperature
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