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(Part 2 of this Unit)
MATTER , ELEMENTS AND THE
PERIODIC TABLE
PA STANDARDS:
3.2.7.A1 – IDENTIFY GROUPS OF ELEMENTS WITH
SIMILAR PROPERTIES
3.2.7.A2 – IDENTIFY ATOMS AS THE BASIC BUILDING
BLOCKS OF MATTER
34. CHAPTER 3, SECTION 1 – ORGANIZING THE
ELEMENTS
Scientists need to organize the elements in a
useful way
 The first Periodic Table of Elements was
proposed by a Russian – Dmitri Mendeleev in
1869

35. OBSERVATIONS MADE BY MENDELEEV
Mendeleev grouped elements that had similar
chemical and physical properties.
 Within these groups, he listed the
elements top to bottom by their
atomic masses;
 The elements also line up in
rows across the table by bonding
power; this is the number of chemical bonds an
element can form by attaching other atoms to
itself.

36. PERIODIC TABLE ARRANGEMENT
Today’s modern table reflects some changes from
Mendeleev’s original (it’s now read leftright)
 The table is called “periodic” because it has a
regular repeated pattern in each row
 Each row is called a period.
 Each column is called a group or family.
 Now the table is listed in order of increasing
atomic numbers (# of positive protons inside the
nucleus)

TODAY’S MODERN PERIODIC TABLE
37. TABLE FACTS:
The atomic number tells how many protons are
inside the atom (#7 N has 7+)
 Elements in the same group
(column) have the same
chemical properties
 The period (row) that an
element is in tells us how many energy levels
(orbital rings) surround the nucleus (ex: N is in
period 2 and has 2 rings)

38. ATOMIC STRUCTURE SUMMARY

At the core of an atom is the nucleus.

The nucleus consists of protons and neutrons.

Electrons are found outside the nucleus in
energy levels (also called orbital rings).
EXAMPLE: ATOMIC STRUCTURE OF HELIUM
Electron (black dot)
Nucleus (dark center)
Helium’s atomic # on the Periodic Table is 2
because it has 2 protons in its nucleus.
39. SUBATOMIC PARTICLES - PROTONS
Protons have a positive charge (+)
 They are found in the nucleus
 Number of protons is the same as the atomic
number
 The # of protons always equals number of
electrons so that + and – charges balance
 The mass of a proton is equal to 1 a.m.u.
(“atomic mass unit”)

40. SUBATOMIC PARTICLES - NEUTRONS

Neutrons do not have a charge; they are neutral

They are found in the nucleus

The mass of a neutron is also 1 a.m.u.

The number of neutrons can vary for one
element; a different # will change the mass of
the atom
41. SUBATOMIC PARTICLES - ELECTRONS

Electrons have a negative charge ( - )

Are found moving outside the nucleus

Electrons have practically no mass

Electrons on the outermost ring control the
chemical behavior of the atom; we call these
outside electrons: valence electrons
ATOMIC STRUCTURE OF SODIUM
QUIZ YOURSELF:

Refer to this block from the periodic table to answer the
following questions for this element:

What is the symbol for this element?

What is the atomic number of this element?

What is the atomic mass of this element?

How many protons does it have?

How many neutrons does it have? (Hint: the
mass comes from counting protons + neutrons)

How many electrons does it have? (Hint: the # of + and – charges in
an atom want to be equal (to cancel out any overall charge)

7
N
Nitrogen
14
QUIZ YOURSELF:
QUIZ YOURSELF:
(Part 3 of this Unit)
CHEMICAL REACTIONS AND EQUATIONS
PA STANDARDS:
3.2.7.A4 – DESCRIBE HOW REACTANTS CHANGE INTO
PRODUCTS IN A CHEMICAL REACTION
42. SYMBOLS
Symbols represent elements.
 They can consist of 1 capital letter or, if has 2
letters, a capital letter and a lower case letter.
 Examples:

 Si
 Silicon
 S  Sulfur
43. CHEMICAL FORMULAS
Formulas represent compounds
 Contain symbols of 2 or more elements
 Subscript # after a symbol show the number of
atoms of that element
(no subscript  assume 1 atom)
 Examples: C02 = 1 carbon, 2 oxygen
HCl = 1 hydrogen, 1 chlorine

WHAT AM I, SYMBOL OR FORMULA?
Si
 NH3
 Co
 NaCl
 C3H8
 Al
 NaHCO3
 CH4
S
