Matter
Chapter 2, Section 1
Elements and the Periodic Table
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Element – a substance that cannot be broken
down into simpler substances by ordinary
chemical or physical means
There are more than 112 known elements, and
new elements continued to be discovered
92 elements occur naturally, the others are
produced in laboratories
The rows in the periodic table are called periods,
and the columns are called groups
Of the known elements, only eight make up most
of Earth’s continental crust (Oxygen, Silicon,
Aluminum, Iron, Calcium, Sodium, Potassium,
and Magnesium); six of which are metals
Concept Check
What is an element?
 A class of matter that contains only one
type of atom; an element cannot be
broken down, chemically or physically, into
a simpler substance with the same
properties.
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Atoms
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An atom is the smallest particle of matter that contains
the characteristics of an element
The central region of an atom is called the nucleus;
the nucleus contains positive charged protons and
neutrons, which have no electrical charge; negatively
charged electrons orbit the nucleus
Protons and neutrons have the same mass
Atomic Number – the number of protons in the
nucleus of an atom
Atoms have the same number of protons as electrons
An electron is the smallest of the 3 fundamental
particles in an atom, with a mass of about 1/1836 the
mass of a proton or neutron
Energy Level – one of several distinct regions around
the nucleus of an atom where electrons are located
Two Models of an Atom
Concept Check
How are electrons, protons, and neutrons
alike and how are they different?
 They are all subatomic particles that make
up atoms. Protons have positive electrical
charges, neutrons have no charge, and
electrons have negative charges. Protons
and neutrons are found in an atom’s
nucleus. Electrons move about the nucleus.
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Isotopes
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Atoms of the same element always have the
same number of protons, but the number of
neutrons for atoms of the same element can
vary
Isotope – an atom with the same number of
protons but different numbers of neutrons for a
given element; an isotope’s mass number is
different from that of a given element
Mass Number – the number of protons and
neutrons in the nucleus of an atom
The nuclei of most atoms are stable, but many
elements have atoms whose nuclei are
unstable; radioactive decay occurs when the
forces that hold the nucleus together are not
strong enough
Carbon Isotopes
Concept Check
What are isotopes?
 Atoms of the same element with the same
number of protons but different numbers of
neutrons.
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Why Atoms Bond
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Most elements exist combined with other elements to
form substances with properties that are different from
the elements themselves
Compound – a substance formed by the chemical
combination of two or more elements in definite
proportions and usually having properties different
from those of its constituent elements
Compounds form when atoms are more stable (exist
at a lower energy state) in a combined form
The chemical process, called bonding, centers around
the electron arrangement of atoms
When an atom’s outermost energy level does not
contain the maximum number of electrons, the atom is
more likely to form a chemical bond with one or more
atoms
Chemical Bond – a force that holds together atoms
that form a compound
Chemical Bonding of Sodium and
Chloride
Concept Check
Why do compounds form?
 Compounds form as a result of changes in
the arrangement of electrons in the
outermost shells of the bonded atoms.
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Types of Chemical Bonds
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An atom that gains electrons becomes negatively
charged, and an atom that loses electrons becomes
positively charged, because the number of protons
and electrons are no longer equal
Ion – an atom or a molecule that possesses an
electric charge
Oppositely charged ions attract each other to form
crystalline compounds
Ionic Bond – a bond that forms between negative
and positive ions
Covalent Bond – a bond that forms when atoms
share electrons
The smallest particle of a covalent compound that
shows the properties of that compound is a molecule
Metallic Bond – a bond that forms when electrons
are shared by metal ions
Ionic Bonds
Covalent
Bonds
Metallic Bonds
Concept Check
What happens when two or more atoms
react?
 Electrons are gained, lost or shared when
two or more atoms react to form a
compound.
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Assignment
Read Chapter 2, Section 1 (pg. 34-43)
 Do Section 2.1 Assessment #1-10 (pg. 43)
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