Transcript 2b Chemistry of Life

The Chemistry of Life
Objectives:
• List the most common elements in
living things
2-1
Basic Chemistry
Matter is anything that takes up space
and has mass.
All matter, living or nonliving, is made up
of elements. Elements can not be
broken down any further through
chemical means.
Elements contain atoms.
An atom is the smallest unit of matter
that can enter chemical reactions.
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Elements
ElementsEssential
Essentialto
toLife
Life
• 96% of our body is made up of oxygen
(O), carbon (C), hydrogen (H), and
nitrogen (N).
• Calcium (Ca), phosphorus (P),
potassium (K), and sulfur (S) and some
trace elements make up the rest.
2-3
The Atom
Atoms have a central nucleus made up of
protons and neutrons, and shells
around the nucleus in which electrons
orbit.
• inner energy shell holds two electrons
• outer energy shell holds eight electrons
The number of electrons in the outer
energy shell determines the chemical
properties of the atom.
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Model
Model of
of an
theAtom
Atom
2-5
The Periodic Table
The atomic number of an atom is its number of
protons.
• protons bear a positive electrical charge
The atomic mass of an atom is its number of
protons plus its number of neutrons.
• neutrons bear no electrical charge
• electrons bear a negative electrical
charge
An electrically neutral atom means:
number of protons = number of electrons
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The Periodic Table
Elements are arranged in a periodic
table:
• horizontally in order of increasing
atomic number
• vertically according to the number of
electrons in the outer shell
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2-8
Isotopes
Some atoms differ in their number of
neutrons and are called isotopes.
Carbon has 3 isotopes:
• Carbon 12 (most abundant)
• Carbon 13
• Carbon 14 (radioactive - unstable)
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Ionic Bonds
In ionic bonding, atoms give up or
accept electrons, resulting in ions.
Ions with opposite charges (- or +) are
attracted to each other and form an
ionic bond.
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Ionic
IonicBonds
Bonds
2-11
Covalent
CovalentBonds
Bonds
In covalent reactions, atoms share
electrons, resulting in covalent
bonds.
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Molecules and Compounds
• Atoms form bonds to fill the outer
shell with electrons.
• When two or more atoms are held
together with covalent bonds,
molecules are formed.
• When atoms of different elements
bond in a fixed ratio, a compound is
formed.
2-13
Wrap-Up
• Review “Show What You Know” with
your partner.
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