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Question: What two particles are found in the nucleus of an atom?
ATOMIC STRUCTURE
Element – matter that is composed of one type of atom
Elements are abbreviated in scientific shorthand – either a letter or a pair of letters
called chemical symbol. Ex: Aluminum – Al Copper – Cu
Atom – smallest piece of matter that still has the properties of the element.
Protons – positive charge (1+)
Neutrons – neutral or no charge
Electrons – negative charge (1-)
Nucleus – located in center of atom consists of protons and neutrons;
electrons surround the nucleus
Electron Cloud – (current) model which shows electrons travelling in specific energy
levels around a nucleus; electrons closest to nucleus have low energy, electrons farther
away have high energy.
Electrons in Energy Levels
Energy Level in Atom
Energy Level in Atom
1
2
2
8
3
18
4
32
* Last energy level can only
hold max of 8 electrons – H
and
He are exceptions
Questions: What is the difference between atomic number and atomic mass?
MASSES OF ATOMS
Smaller particles of matter called quarks exist but scientist still consider atoms the
basic building blocks of matter
Quark – smaller particles that make up protons and neutrons – six quarks are to exist
Atomic mass – composed mostly of protons and neutrons in the nucleus – also called
mass number
Atomic number – the number of protons in an atom; number of protons also identifies
the element
* If you needed to find # of neutrons of an atom:
# of Neutrons = mass number – atomic number
Isotopes – atoms of the same element that have different number of neutrons.
B10 (Boron – 10) or B11 (Boron – 11)
Different isotopes have different properties.
Average atomic mass – weighted average mass of an elements isotopes.
Common Mass Numbers
Element
BORON
CARBON
OXYGEN
SODIUM
COPPER
Symbol
B
C
O
Na
Cu
Atomic No.
5
6
8
11
29
Protons
5
6
8
11
29
Neutrons
6
6
8
12
34
Mass
11
12
16
23
63
Ave. Atomic Mass
10.81 amu
12.01 amu
16 amu
22.99 amu
63.55 amu
Question: What do elements in the same group have in common?
THE PERIODIC TABLE
Periodic table – table where elements are organized by increasing atomic number
(number of protons)
In the late 1800’s, Dmitri Mendeleev devised first periodic table based on atomic mass –
however, some elements were out of order. In 1913, Henry G. J. Moseley arranged
elements by atomic number and is what we use today.
The periodic table is arranged by groups and periods
Groups – vertical columns of elements with similar properties - groups are
numbered 1-18.
 elements in the same group have the same number of electrons in their outer
energy level
Periods – horizontal rows of elements that contain increasing numbers of protons and
electrons. Period are numbered 1-7
 each row in the periodic table ends when an outer energy level is filled
Each of the seven energy levels can hold a maximum number of electrons.
Level 1 – 2 electrons Level 2 – 8 electrons
* outer level can hold a max of 8 electrons – except Hydrogen & Helium (only max 2)
Electron Dot Diagram – use the element symbol and dots to represent outer energy level
electrons.
He
O
Ne
Al
Question: Which of the following would be the best conductor – iodine, silver, silicon or sulfur?
METALS, NONMETALS & METALLOIDS
Metals – good conductor of heat and electricity, all but mercury are solid at room
temperature
* Metals are located to the left of stair step
Alkali Metals – (Group 1) are the most reactive of all metals; don’t occur in nature in
their element form
Alkaline Earth Metals – (Group 2) shiny, ductile and malleable; combine readily with
other elements
Transition Elements – (Group 3 – 12) most familiar metals because they often occur in
nature uncombined
Inner Transition Metals – (listed below table)
 Lanthanide Series – elements with atomic # 58 – 71
 Actinide Series – elements with atomic # 90 – 103
Nonmetals – elements that are usually gases or brittle solids at room temperature; most
can form ionic and covalent compounds – located to the right of the stair step.
Noble gases – (Group 18) exist as isolated atoms. They are all stable because outer energy
level is filled
Metalloids – elements that make up stair step; have me have metallic and non-metallic
properties
Metalloids are part of the mixed groups – which contain metals, non-metals and
metalloids (mixed groups are Group 13, 14, 15, 16, 17)