Atoms of the same element that differ
in the number of neutrons they contain
All isotopes of the same element
have same number of electrons
Chemical Compounds/Bonds
Chemical Compounds
Substance formed by the chemical combination
of two or more elements in definite proportions
Shown as chemical formula
Example: water is H20
Example: table salt is NaCl
Physical properties of a compound
are usually different from those of
the elements from which it formed
Chemical Bonds
Atoms in compounds are held
together by chemical bonds
Ionic bonds
Formed when one or more electrons are
transferred from one atom to another
Ions
An atom that loses or gains electrons
Covalent bonds
Formed when electrons
are shared by atoms
Molecule
The structure that results when atoms
are joined together by covalent bonds
Properties of Water
and Suitabilty for Life
Polarity
A molecule in which the
charges are unevenly distributed
similar to a magnet with two poles
Hydrogen Bonding
Solvent
Substance in which the solute dissolves
Water expands slightly upon freezing
Makes ice less dense than water
That's why ice floats
Attraction between a hydrogen atom
with a partial positive and another
atom with a partial negative charge
Heat Capacity
Takes large amount of heat energy to
cause the molecules to move faster
Importance of Carbon to Life
Carbon has four valence electrons,
allowing them to form strong covalent
bonds with many other elements
One carbon atom can bond to another
which gives carbon the ability to form
chains that are almost unlimited in length
Macromolecules
Carbohydrates
Living things use carbohydrates as their main source
of energy; sometimes used for structural purposes
Lipids
Can be used to store energy. Some are important parts
of biological membranes and waterproof coverings
Nucleic Acids
Store and transmit hereditary, or genetic, information
Proteins
Control rate of reactions and regulate cell processes. Some
form important cellular structures, while still others transport
substances into or out of cells or help fight disease
Chemical Reactions and Enzymes
Chemical Reactions
Process that changes, or transforms,
one set of chemicals into another
Chemical reactions involve changes in the
chemical bonds that join atoms in compounds
Chemical reactions that release
energy often occur on their own
Chemical reactions that absorb energy
will not occur without a source of energy
Enzymes
Speed up chemical
reactions that take
place in cells
Temperature, pH, and
regulatory molecules
can affect the activity
of enzymes