Chapter 4 Section 1 Notes
Matter
- matter – anything that takes up space (has volume) and
has mass
o mass – amount of matter in an object
o matter also has density (D=mass/volume)
o matter also shows gravity
Properties of Matter
- physical properties – characteristics that can be observed
without changing the identity of the object
o density
o color
o hardness (Mohs Hardness Scale)
o freezing/melting point
o boiling point
o conductivity of electricity
- chemical properties – characteristics that describe how a
substance can react with other substances to produce new
substances
o iron reacting oxygen to form rust
o burning of paper
- physical change – any change to a substance that does not
change the identity of the object
o tearing
o boiling/freezing/melting
- chemical change – the ability of an object to change into a
new substance
o burning
o forming rust
Elements
- a substance that cannot be broken down into simpler
substance through ordinary chemical means
- each element has a characteristic set of properties
o chemical
o physical
- more than 90 occur naturally
- eight make up more than 98% of Earth’s crust (fig. 1
page 81)
Atoms
- the smallest unit of an element that has the properties of
that element
- cannot be broken down into smaller particles and have
the same properties
- about 1 000 000 atoms stacked side to side will equal the
thickness of a single piece of paper
Atomic Structure
- subatomic particles – small particles that make up atoms
o proton
 positive charge
 located in the nucleus
 mass of 1 amu
o neutron
 neutral charge
 located in the nucleus
 mass of 1 amu
o electron
 negative charge
 located in the electron cloud
 no mass (1/1820 of a proton)
The Nucleus
- small region in the center of the atom
o proton
o neutron
- positive charge
- makes up most of the mass of the atom
- very little of the volume of the atom
- an atom is mostly empty space
The Electron Cloud
- region of space around the nucleus that holds electrons
- the attraction of the electrons to the nucleus holds the
electrons in place
Atomic Number
- number of protons in the nucleus
- all atoms of a given element have the same atomic
number
- sets the atoms apart from other atoms
- atomic number is equal to the number of electrons of an
electrically neutral atom
- periodic table
o a system (chart) for classifying elements
o elements in the same column have similar
arrangements of electrons
o elements in the same column have similar properties
 physical
 chemical
Atomic Mass
- mass number – sum of the number of protons and
neutrons
- expressed in atomic mass units (amu)
- electrons add very little to the total mass, therefore, their
mass is not calculated
Isotopes
- atoms that have the same atomic number but have a
different atomic mass
- number of neutrons differ
- different isotopes of the same element have slightly
different properties
o Hydrogen
 Protium (1 proton, 0 neutrons)
 Deuterium (1 proton, 1 neutron)
 Tritium (1 proton, 2 neutrons)
Average Atomic Mass
- the weighted average of the atomic masses of the
naturally occurring isotopes of an element
- weighted average of the atomic masses determine the
average atomic mass
Valence Electrons and Periodic Properties
- elements on the are arranged in columns based on
similarities
- groups – columns of the periodic table
- determined by the number of valence electrons
o valence electrons – outermost electrons of an atom
- groups 1 and 2 have 1 and 2 valence electrons respectively
- groups 13 – 18 have group number minus 10 valence
electrons
- groups 2 -1 2 have two or more valence electrons
o metals – atoms that have 3 or fewer valence
electrons
o nonmetals – atoms that have 4 or more valence
electrons