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Elements:
 pure substances with only one type of atom.
 Each element has its own distinct properties.
 cannot be broken down into simpler parts by a chemical
change.
Compounds:
 pure substances made of more than one type of atom.
 Compounds are made of elements.
 NaCl (sodium chloride) is an example of a compound.
Dalton’s Theory of the Atom
 All matter is composed of tiny, indivisible particles
called atoms.
 All atoms of an element have identical properties.
 Atoms of different elements have different
properties.
 Atoms of two or more elements can combine in
constant ratios to form new substances.
 In chemical reactions, atoms join together or
separate from each other but are not destroyed.
The Language of Chemistry
Chemical formula: uses symbols and numbers to represent what types
of atoms are in a compound.
Molecule:
a group of atoms bonded together. (Yes, compounds are
molecules!)
Word Equations:
describe chemical changes or chemical reactions.
sodium + chlorine  sodium chloride
Na
+
Cl
 NaCl
What Are Atoms Made Of?
Atoms consist of:
1.
A nucleus made of positively charged protons and non-charged
neutrons.
2.
A group of organized negatively charged electrons.
Electrons are organized into compartments or orbitals called “shells”.
Format for writing
elements outside of
the periodic table:
Subatomic Particles
Subatomic
Particle
Electron
Proton
Neutron
Charge
Symbol
Mass (g)
11+
0
ep+
n0
9.02x10-28
1.67x10-24
1.67x10-24
 atomic mass units (u) are used on the periodic table, NOT grams
 1 proton = 1u
 1 neutron = 1u
Mass # = # protons +# neutrons
Atomic # = # of protons (and # electrons in a neutral atom)