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Biology
Chapter 2
Chemistry of Life
Composition of Matter


Matter is anything that occupies space and has mass
Mass is the quantity of matter an object has
o Mass vs. Weight
 Weight is determined by the force of gravity acting on a mass
 Example: The same mass would have less weight on the moon
than on the Earth

Elements and Atoms
o Elements are substances that cannot be broken down chemically into simpler
kinds of matter
 There are over 100 elements, fewer than 30 are important to living things
 90% of the mass of all living things are composed of just four elements
 Carbon
 Hydrogen
 Oxygen
 Nitrogen
 Elements are organized in the periodic table
 Each element has a different chemical symbol
 Each symbol consists of 1,2,or 3 letters
 The symbol is derived from the first letter or other letters in the
name of the element…Ex: Chlorine-Cl
 Most other names are derived from Latin names
o Atoms- are the simplest particles of an element that retains all the properties of
that element. They cannot be seen with the naked eye

Nucleus is the central part of an atom and makes up the bulk of the mass
of an atom
 It consists of two kinds of subatomic particles
1. Protons- positively charged particles
2. Neutrons- neutral particles
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

Atomic number- the number of protons in the nucleus of an atom
Mass number- is equal to the total number of protons and neutrons of the
atom
o Electrons are negatively charged particles found orbiting the nucleus of an atom
and are the third sub-atomic particle
 The number electrons equals the number of protons so an atom is
electrically neutral
 They are high energy particles that have very little mass
 They are found moving around the nucleus at very high speeds and are
located in orbitals
 An orbital is a three-dimensional region around a nucleus that indicates the
possible location of an electron
 Electrons in orbitals that are farther away from the nucleus have greater
energy than electrons in orbitals closer to the nucleus
 When all orbitals are combined there is a cloud of electrons surrounding the
nucleus
 Orbitals correspond to specific energy levels
 The first energy level can only hold 2 electrons
 The second energy level can hold up to 8 electrons
o Isotopes are atoms of the same element that have a different number of
neutrons
 Additional neutrons change the mass of the element
 Example: Hydrogen has several isotopes
 Protium- 1 proton + 0 neutrons
 Deuterium- 1 proton + 1 neutron
 Tritium- 1 proton + 2 neutrons

Compounds are made up of atoms of two or more elements in fixed proportions
o A chemical formula shows the kinds and proportions of atoms of each element
that forms a particular compound
 Example: H2O is the chemical formula for water. It has 2 atoms of
Hydrogen and 1 atom of oxygen
o The physical and chemical properties of a compound are often very different
from the physical and chemical properties of the elements that make them up
 Example: Hydrogen is an unstable, highly flammable gas at room
temperature. Oxygen is a gas, that, at room temperature,
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promotes combustion…water, however, is a liquid that is very
stable, is used to put out fires, and is essential for life
o How elements combine and form compounds depends on the number and
arrangement of electrons in their energy levels
o An atom is chemically stable when the its highest energy level is filled with the
maximum number of electrons
o Some elements such as Helium and Neon consist of atoms that have the
maximum number of electrons in their highest energy level.
 These elements are called noble or inert elements (gases) and do not
react with other elements under normal conditions
o Most elements are not stable and tend to react with other elements to achieve
stability
 Chemical Bonds are the attractive forces that hold atoms together
 Covalent bonds form when two atoms share one or more pairs of
electrons
o The electrons in an atom’s outermost energy level are
called valence electrons
o An atom achieves stability when its outermost energy level
is complete
o Hydrogen has one electron so it needs one more to fill its
first energy level to achieve stability
o Oxygen has 8 electrons, 2 in the first energy level and 6 in
the second.
o Hydrogen and oxygen will share electrons with each other
but in order to do so they must get very close to each other
o When they share electrons they are no longer individual
atoms. They become water.
o When a compound forms, the physical and chemical
properties of the newly formed compound are very
different from the elements they are composed of
 Example: Water….it consists of 2 hydrogen atoms
and 1 oxygen atom
 Hydrogen- is a gas, highly unstable,
flammable
 Oxygen- is a gas, unstable, and promotes
combustion
 Water- is a stable liquid used to put out fire
and is essential to all living things
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o Molecule is the simplest part of a substance that retains all
of the properties of that substance
 Example: One molecule of the compound water is
H2O, and one molecule of oxygen gas is O2

Ionic Bonds- form from the attractive force between oppositely
charged ions
o An ion is a charged particle
 Atoms will either gain or lose valence electrons to
achieve stability
 When they do they become either positively
charged or negatively charged
o Sodium Chloride (NaCl) is table salt and forms from a Na+
ion bonding with a Cl- ion
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Example of ionic bonding between sodium and chlorine
o Once Sodium loses an electron it becomes more positively
charged
o When Chlorine gains an electron it becomes more negatively
charged
o Opposites attract and an ionic bond forms
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Energy- The ability to do work
o States of Matter
 Solids maintain a fixed volume and shape. The molecules move less
rapidly than liquids or gases
 Liquids maintain a fixed volume, but its particles move more freely than a
solid, this gives a liquid the ability to flow and conform to the shape of
any container
 Gases are composed of particles that move the most. They occupy the
space available to them
o Thermal energy must be added or removed for a substance to change states of
matter

Energy and Chemical Reactions
o A chemical reaction occurs when one or more substance change to produce one
or more different substances
o Energy is absorbed or released when chemical bonds are broken or new ones are
formed
o The following is an example of a chemical reaction
 CO2 + H2O  H2CO3
 CO2 and H2O are the reactants. Reactants are found on the tail
side of the arrow
 H2CO3 is the product. Products are found on the head of the
arrow
o There are thousands of chemical reactions that occur inside the human body
 Reactions that break down food we eat for energy
 Reactions that build muscle
 Reactions that regulate the amount of sugar in our blood
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o Activation energy is the amount of energy needed to start a chemical reaction
 Catalysts speed up the rate of the reaction by lowering the amount of
activation energy needed to start the reaction
 In living things enzymes act as catalysts. An enzyme is a protein or RNA
molecule that speeds up a metabolic reaction without being permanently
changed or destroyed
o Oxidation Reduction Reactions
 Reactions in which electrons are transferred between atoms…also known
as redox reactions
 Oxidation reactions – a reactant loses one or more electrons,
thus becoming more positive
 Reduction reactions- a reactant gains one or more electrons, thus
becoming more negative
Water and Solutions

Polarity – the uneven distribution of electrical charges on a molecule
o Hydrogen and oxygen bond covalently to form water
o The atoms do not share the electrons evenly
o The oxygen atom has a greater ability to attract hydrogen’s electrons to
its nucleus
o As a result, the region of the molecule where the oxygen atom is located
has a partial negative charge. And the region of the molecule where the
hydrogen atoms are has a partial positive charge
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o The polar nature of water allows it to dissolve polar substances such as
sugar, ionic compounds, and some proteins
o NaCl is a polar substance found in our bodies in the form of dissociated
ions of Na+ and Clo They are essential for bodily functions such as muscle
contractions and the transmission of nerve impulses

Hydrogen bonding is the force of attraction between a hydrogen atom or
molecule with a partial positive charge and another atom or molecule with a
partial or full negative charge
o Example: Water molecules are attracted to other water molecules
 The negative side of a water molecule is attracted to the positive
side of another water molecule
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
Cohesion and Adhesion
o Cohesion is the attractive force that holds molecules of a single
substance together
 Example: Water sticking to water. This creates surface tension
and allows small insects and other organisms to be able to walk
on water
o Adhesion is the attractive force between two particles of different
substances
 Example: water attracted to glass
o Capillarity: is the attraction between molecules that results in the rise of
the surface of a liquid when in contact with a solid

Density of Ice
o Ice is less dense than liquid water
o This is due the shape of the water molecule and hydrogen bonding
o When water becomes a solid the angles between the hydrogen atoms is
wider so there is more open space
o This lower the density of ice
Solution

A solution is a mixture in which one or more substances are uniformly distributed in
another substance
o Solute: the substance dissolved in the solvent
 Example: Sugar dissolves in water
o Solvent: the substance in which the solute is dissolved

Saturated solution is one in which no more solute can be dissolved
o Temperature can affect the quantities dissolved

Aqueous solutions are solutions in which water is the solvent
o Body cells exist in aqueous solutions
o Marine organisms live in aqueous solutions
Acids and Bases are a measure of the relative amounts of hydronium ions (H3O+) and hydroxide
ions (OH-) in a solution
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Acids have a greater number of hydronium ions in solution
o Strong acids have a high number of hydronium ions in solution
o They tend to have a sour taste
Bases have a greater number of hydroxide ions in solution
o Strong bases have a high number of hydroxide ions in solution
o Alkalinity is another word used to describe a basic solution
o They are slippery to the touch
pH
Buffers
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