Download Nature of Matter

Chapter # 2 – The Chemistry of Life
I. The Nature of Matter
-Life depends on
Chemistry….Chemical reactions
in our body keep us alive & all
things are made of chemical
compounds.
A. Atoms – atomos (unable to be cut)
Atom – the basic unit of matter.
The atom contains 3 subatomic particles
1. Protons – positively
charged particles.
2. Neutrons – particles
with no charge.
3. Electrons – negatively
charged particles that
are constantly in
motion outside of the
nucleus.
Atomic Nuclei
-Protons + Neutrons = the nucleus
Nucleus – the center of
the atom which contains
the protons & the neutrons.
-Atoms are neutral because
they have equal numbers of
protons & electrons.
-Atomic mass = # protons + # neutrons
B. Elements & Isotopes
Element – a pure substance
that consists entirely of
one type of atom.
-Over 100 elements are
known, but only about 24
are found in living organisms.
-Elements are represented by
symbols, Ex : C = Carbon,
H = Hydrogen, etc.
-An element’s atomic number = #
protons in an atom of the element.
Atomic mass – # protons = # neutrons.
Isotopes
Isotopes – atoms of
the same element
that have different
numbers of neutrons,
Ex : C12,C13, C14
-Are identified by
mass number.
-Because they have the same # of electrons, all isotopes
of an element have the same chemical properties.
Radioactive Isotopes
Radioactive isotopes –
isotopes with unstable
nuclei that break down at a
constant rate over time.
-Used to date
specimens, treat
cancer, & kill bacteria.
C. Chemical Compounds
Compound – a substance
formed by the chemical
combination of 2 or more
elements in definite
proportions.
-The composition of
compounds is shown as a
chemical formula, Ex : Water is
made of 2 hydrogen atoms & 1
oxygen atom. Its chemical
formula is H2O.
D. Chemical Bonds
-Atoms in compounds are held
together by chemical bonds.
-Bonding happens between
electrons that surround atomic
nuclei. Electrons that are available
to bond are called valence
electrons.
2 Major Types of Bonds
1. Ionic – when 1 or more
electrons are transferred
from 1 atom to another.
2. Covalent – when electrons
are shared between atoms.
In Ionic bonding :
Ions – are positively or
negatively charged atoms.
Atoms become ions if they :
1. Lose electrons = become
positive (cation).
2. Gain electrons = become
negative (anion).
Types of Covalent Bonds :
1. Single bond – when
atoms share 2
electrons (1 pair of
electrons).
2. Double bond – when
atoms share 4
electrons (2 pairs
of electrons).
3. Triple bond – when
atoms share 6
electrons (3 pairs of
electrons).
Molecules & van der Waals forces
-Atoms are joined together
by covalent bonds, to form
molecules – the smallest
unit of most compounds.
-Electron sharing isn’t always
equal.
van der Waals forces –
a slight attraction that
develops between the
oppositely charged
regions of nearby
molecules.