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Atomic Structure
Matter
Anything that has mass and
takes up space
 Matter can take many forms
and is not always visible to the
eye
 Matter can change form

Matter is made of atoms
 Matter can neither be created
nor destroyed; it just changes
form - Law of Conservation of
Matter

Atoms
Tiny particles that make up
matter
 They are so small that 1 million
atoms lined up side by side are
equal to the thickness of a
human hair

“atom” comes from a Greek
word that means “cannot be
divided”
 Atoms are made of small
subatomic particles called
protons, electrons, and
neutrons

Proton
Positively charged particle
 Located in the nucleus of an
atom
 Mass = 1 atomic mass unit
 Number: the number of protons
equals the number of electrons

Electron
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Negatively charged particle
Located outside the nucleus of an
atom
Mass is almost 0 (1/2000 of a
proton)
Number: the number of electrons
equals the number of protons
Neutron
Neutral particle, no charge
 Located in the nucleus of an
atom
 Mass = 1 atomic mass unit
 Number: the number of neutrons
varies

Nucleus

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Contains most of the mass of an
atom
Total number of particles in the
nucleus is equal to the number of
protons plus the number of
neutrons
Model of the Atom
Protons and neutrons are found
in the nucleus, the dense center
of an atom
 Nucleus is positively charged protons are positively charged
and neutrons have no charge

Electrons are found in a cloud
around the positively charged
nucleus
 The electrons are very far away
from the nucleus, so the atom is
mostly empty space

Nucleus

Most of the mass of the atom is
located in the nucleus because
electrons are so small compared
to mass of protons and neutrons
Electrons
Electrons are arranged in energy
levels around the nucleus, these
are sometimes called energy
shells
 Electrons are negatively charged
particles

Lowest energy level is closest to
the nucleus and can contain only
2 electrons
 Higher energy levels, further from
the nucleus can contain more
electrons

Level 2 can hold 8 electrons, level
3 can hold up to 18, and level 4
up to 32
 There are up to 7 energy levels
for electrons

Types of Matter - Elements
Most kinds of matter are made of
combinations of a basic group of
building blocks called elements
 Element - matter made up of only
one type of atom

Natural elements
There are about 112 known
elements today; 90 of these are
naturally occurring elements, the
rest are synthetic
 Naturally occurring elements are
found in nature

Synthetic elements
Synthetic elements are manmade in laboratories. These
elements may exist naturally in
stars, but on Earth they exist only
when made in a lab
 Synthetic elements are unstable

Periodic table
Elements are organized into a
chart called the periodic table
 They are organized by the
number of protons in their nuclei
 Mendeleev came up with the idea
of classifying elements into a
table

Element name and symbol

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Each element has a name and an
abbreviation known as its atomic
symbol
Atomic symbols consist of 1, 2, or 3
letters. The first letter of the
symbols is capitalized and the rest
are lower case


New synthetic elements have the 3
letter symbol that represents their
number and later are assigned a 2
letter symbol
For example Element 114 was
called Ununquadium, Uuq, until it
got its final name Flerovium, Fl
Atomic number

The atomic number of an
element indicates the number of
protons in the nucleus of that
element
Atoms are electrically neutral
 The number of protons is equal
to the number of electrons

Atomic mass of an atom

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The atomic mass is a number that
indicates the mass of the atoms of
that element in atomic mass units,
symbolized by the letter u
Atomic mass is equal to the
number of protons + the number
of neutron in the nucleus
Information on the periodic table
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Element name ----->
Atomic number ---->
Atomic symbol ---->
Atomic mass ------>
Chlorine
17
Cl
35.453
Isotopes
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All the atoms of an element have
the same number of protons
There are different forms of an
element called isotopes
Isotopes differ from each other
because they have different
numbers of neutrons
Isotopes
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Isotopes have the same number of
protons, but different numbers of
neutrons
Isotopes have different masses
Isotopes
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C-12 and C-14 are isotopes of
carbon
C-12 or Carbon-12, has a mass of
12 u , 6 protons and 6 neutrons
C-14 or Carbon-14, has a mass of
14 u , 6 protons and 8 neutrons
Isotopes
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Isotopes are named by writing the
name or symbol for the element
followed by a hyphen and the
atomic mass of the element
Ag-107 is silver with an atomic
mass of 107,
protons 47, neutrons 60
Average atomic mass

Because elements have various
isotopes, the atomic mass reported
in the Periodic Table is an average
of the masses of the various
isotopes of the element
Average atomic mass

The amounts (percentages) of each
isotope in a sample is accounted
for when the average atomic mass
is calculated
Ions
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Atoms that have the same number
of electrons and protons are
neutral and have no charge
Sometimes atoms can be positively
or negatively charged – atoms that
have a charge are called ions
Ions
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Ions with more electrons than
protons are negatively charged
Ions with more protons than
electrons are positively charged
Ions: anions
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Negative ions are called anions
O2-, Oxygen ion with 8 protons
and 10 electrons, has a charge of
-2
Ions: cations
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Positive ions are called cations
Mg2+ Magnesium ion with 12
protons and 10 electrons, it has a
charge of +2
Atomic identity

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Number of protons controls the
identity of an element
Change the number of protons and
you change to a new element
Atomic reactivity
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Number of electrons controls the
reactivity of an element
Atoms can add or lose electrons
and still keep their identity
Atoms that add or lose electrons
are charged and are called ions
Periodic Table
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Mendeleev, a Russian scientist first
organized all the elements known
in the late 1800’s
He discovered repeating patterns in
chemical properties
He arranged the elements in order
of increasing atomic mass
Modern Periodic Table

The periodic table is a table of the
chemical elements in which the
elements are arranged in order of
atomic number in such a way that
the periodic properties (chemical
periodicity) of the elements are
made clear.
Modern Periodic Table
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Elements are arranged in order of
increasing atomic number
Increase in atomic number from
left to right
Modern Periodic Table -Periods
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Rows are called periods (horizontal)
Elements in the same period have
the same number of energy levels
for their electrons
Modern Periodic Table - Groups
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Columns are called groups or
families (vertical)
Elements in the same column have
similar chemical properties
They have different numbers of
electrons, but the same number of
outer (valence) electrons
Modern Periodic Table
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Metals are to the left of the
periodic table
Non-metals to the right
Metalloids are stair steps on right,
between metals and non-metals
Periods
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Numbered from 1 to 7
6th and 7th periods also contain the
rows at the bottom of the table
Groups
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Numbered from 1 to 18
Also called families
Each group of elements has
characteristic chemical and physical
properties that can assist in their
identification
Group 1
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Alkali metals
Easily react with water
1 valence electron
Hydrogen is in Group 1 because it
has 1 valence electron, but it is not
a metal
Group 17
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Halogens
Extremely reactive
7 valence electrons
Nonmetals
Tend to form negative ions and
gain 1 electron
Group 18
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Noble or Inert Gases
Extremely unreactive, usually don’t
bond with other elements
8 valence electrons (He has 2)
Outer energy level can’t hold any
more electrons
Nonmetals
Metals
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Groups 1-12 and parts of 13-17
Shiny or lustrous in appearance,
hard, malleable, ductile (can be
pulled into wires)
Conduct heat and electricity very
well
Metals
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Tend to form positive ions and give
away or share 1 to 4 electrons
Most of the elements in the
Periodic Table are metals
Find them on the left and the
center of the Table
Nonmetals
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Can be gases or solids at room
temperature
Belong to Groups 14 - 18
Find them on the upper right
corner of the Periodic Table
Nonmetals
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Soft, brittle, and dull in appearance
Poor conductors of heat or
electricity
Can share electrons or gain 1, 2, or
3 electrons to form negative ions
Metalloids
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Select elements in Groups 13-17
B, Si, Ge, As, Sb, Te, Po, and At
Found along the boundary between
metals and nonmetals, along a
stairstep
Not all scientists agree as to the
exact elements in this group
Metalloids
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Can be shiny or dull, soft or hard,
malleable or brittle
Can conduct electricity, but not as
well as metals (semi-conductors)
Chemical Reactivity

An example of chemical reactivity is
when two or more elements
combine to form compounds or
molecules (if two of the same
elements bond together)
Inorganic Compounds
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Compounds of metal atom(s) and
one or more nonmetal atoms
Often form ionic bonds with metal
cation(s) (+) and nonmetal
anion(s) (-)
Result in a neutral compound, also
called a salt
Organic Compounds
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Compounds that do not usually
contain metal atoms
Often have C and H atoms bonded
together by covalent (shared
electrons) bonds
Also contain O, N, and S