Everything is made of atoms. Atoms are the smallest part of matter.
Atoms are made up of 3 subatomic particles (particles smaller than the atom): electrons, protons, and neutrons.
Negatively charged
particles; outside
the nucleus; can electrons
be gained or lost
to and from other at-
oms; very small mass:
1/2000th of a proton
Neutral particles neutrons
in the nucleus; give
mass to the atom,
but not charge.
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On the following diagram of an atom define
the parts of the atom.
Cl₂-
Na-
nucleus
Center of the atom;
contains protons and neutrons.
Atoms combine into molecules.
O is an atom; O₂ is a molecule: both are oxygen.
Molecules are made up of two or more atoms.
The Atom
Atom, molecule or compound?
NaCl-
Count the protons to tell what element this is:
# of Protons: Element:
If two different atoms combine they make compounds:
H₂O is a compound; O₂ is a molecule.
Compounds are made up of two or more elements.
protons
Positively charged
particles; in
the nucleus;
determine what
element an atom is.
Atoms, Molecules, and Compounds
Na-
CI-
●
John Dalton in 1808 published a theory of the
atom that had these important points:
●
All atoms of a particular element are the
same.
Atoms of different elements have
different properties, mass, and chemical re-
activity.
Water molecule-
a compound (H₂O)
Atoms are not changed by chemical reac-
tions, just rearranged in order or number.
2 hydrogens
(H)
C
H
What elements are these?
Ch. 18:1
This model of the atom looks a
lot like a solar system. The
nucleus, which contain the pro-
tons and neutrons, in the center
would be the sun. The
electrons are the planets
spinning around the nucleus.
1 oxygen
Oxygen molecule-
an element (0₂)
O
2 oxygens
by C. Stephen Murray, 2003