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Earth Chemistry
Section 1: Matter
Preview
• Objectives
• Comparing Physical and Chemical Properties
• Properties of Matter
• Atomic Structure
• Parts of the Atom
• Atomic Number
• Periodic Table Overview
• Atomic Mass
• Valence Electrons and Periodic Properties
Section 1
Earth Chemistry
Section 1
Objectives
• Compare chemical properties and physical properties of
matter.
• Describe the basic structure of an atom.
• Compare atomic umber, mass number, and atomic
mass.
• Define isotope.
• Describe the arrangement of elements in the periodic
table.
Earth Chemistry
Section 1
Properties of Matter
• matter *
• Every object in the universe is made up of particles of
matter. The amount of matter in any object is the mass
of that object.
• All matter has two types of distinguishing properties-*.
Earth Chemistry
Section 1
Properties of Matter, continued
• Physical properties are characteristics that can be
observed without changing the composition of the
substance.
• Physical properties include density, color, hardness,
freezing point, boiling point, and the ability to conduct an
electric current.
• Chemical properties are characteristics that describe
how a substance reacts with other substance to produce
different substances.
Earth Chemistry
Section 1
Properties of Matter, continued
Elements
• element a substance that cannot be separated or
broken down into simpler substances by chemical
means;
• Each element has a characteristic set of physical and
chemical properties that identify it.
• Every known element is represented by a symbol of one
or two letters.
Earth Chemistry
Section 1
Properties of Matter, continued
Atoms
• Elements are made of atoms.
• atom *
• A single atom is so small that its size is difficult to
imagine.
Earth Chemistry
Section 1
Atomic Structure
• Even though atoms are very tiny, they are made up of
smaller parts called subatomic particles.
• There are three types of subatomic particles—protons,
electrons, and neutrons.
• proton *
• electron *
• neutron *
Earth Chemistry
Section 1
Atomic Structure, continued
The Nucleus
• The protons and neutrons of an atom form the nucleus.
• The positively charged nucleus makes up most of an atom’s
mass but very little of its volume. The volume of an atom is
mostly empty space.
The Electron Cloud
• The electrons of an atom move in a certain region of space
called an electron cloud that surrounds the nucleus.
• The negatively charged electrons are attracted to the
positively charged nucleus. This attraction holds electrons in
the atom.
Earth Chemistry
Parts of the Atom
Section 1
Earth Chemistry
Section 1
Atomic Number
• The number of protons in the nucleus of an atom is
called the atomic number.
• All atoms of any given element have the same atomic
number. An element’s atomic number sets the atoms of
that element apart from the atoms of all other elements.
• Elements on the periodic table are ordered according to
their atomic numbers.
• Elements in the same column on the periodic table have
similar arrangements of electrons in their atoms, and
therefore have similar chemical properties.
Earth Chemistry
Section 1
Atomic Number, continued
The diagram below shows the atomic numbers and mass
numbers of three elements.
Earth Chemistry
Atomic Number, continued
The diagram below shows the periodic table.
Section 1
Earth Chemistry
Periodic Table Overview
Section 1
Earth Chemistry
Section 1
Atomic Mass
• The sum of the number of protons and neutrons in an
atom is the mass number.
• The mass of a subatomic particle is too small to be
expressed easily in grams, so a special unit called the
atomic mass unit (amu) is used.
• Protons and neutrons each have an atomic mass close
to 1 amu.
• Electrons have much less mass than protons or neutrons
do. The mass of 1 proton is equal to the combined mass
of about 1,840 electrons.
Earth Chemistry
Section 1
Atomic Mass, continued
Isotopes
• Although all atoms of a given element contain the same
number of protons, the number of neutrons may differ.
• isotope *
• Because of their different number of neutrons and their
different masses, different isotopes of the same element
have slightly different properties.
Earth Chemistry
Section 1
Atomic Mass, continued
Average Atomic Mass
• Because isotopes of an element have different masses,
the periodic table uses an average atomic mass of each
element.
• The average atomic mass is the weighted average of the
atomic masses of the naturally occurring isotopes of an
element.
Earth Chemistry
Section 1
Valence Electrons and Periodic Properties
• Based on similarities in their chemical properties,
elements on the periodic table are arranged in columns,
which are called groups.
• An atom’s chemical properties are largely determined by
the number of the outermost electrons in an atom’s
electron cloud. These electrons are called valence
electrons.
• The elements that form each group commonly have the
same number of valence electrons.
Earth Chemistry
Section 1
Valence Electrons and Periodic Properties,
continued
• When an atom has 8 valence electrons, it is considered
stable, or chemically unreactive. Unreactive atoms do not
easily lose or gain electrons.
• Elements whose atoms have only one, two, or three
valence electrons tend to lose electrons easily. These
elements have metallic properties and are generally
classified as metals.
• Elements whose atoms have from four to seven valence
electrons are more likely to gain electrons. Many of these
elements are classified as nonmetals.