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Periodic Table Trends
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•I CAN identify trends among the element on
the periodic table.
Trends Within The Periodic Table
• Recall the modern periodic table is organized by INCREASING ATOMIC
NUMBER.
• Elements with SIMILAR PROPERTIES for the VERTICAL COLUMNS
called FAMILIES/GROUPS.
• Across the periodic table, HORIZONTAL ROWS of elements are called
PERIODS/SERIES.
• Within the periodic table, there are a number of PATTERNS among
the element that help describe their CHEMICAL PROPERTIES.
• We will look at the two most important ones: ATOMIC RADIUS and
ELECTRONEGATIVITY.
ATOMIC RADIUS (RADII)
• One property of the elements that can been seen on the periodic
table is ATOMIC RADIUS.
• ATOMIC RADIUS is a measure of the SIZE OF AN ATOM.
• Since an atoms is not a SOLID SPHERE, it has no distinct OUTER EDGE.
Therefore is would be difficult to measure the width of an atom:
• In order to find the size of an atom, chemists measure from the
CENTER OF THE NUCLEUS of one atom to the CENTER OF THE
NUCLEUS of the next one, then DIVIDE THE DISTANCE BY 2.
ATOMIC RADIUS = DISTANCE
2
• The ATOMIC RADIUS of the atoms that make up the elements VARY
GREATLY within the periodic table.
• Look at this diagram which illustrates the AVERAGE ATOMIC RADIUS
of the atoms of the periodic table.
• What GENERAL CONCLUSIONS can you draw about ATOMIC RADIUS?
ATOMIC RADIUS
What general conclusions can you draw about
atomic radius?
• In general ATOMIC RADIUS:
• 1. DECREASES LEFT TO RIGHT across the periodic table.
• 2. INCREASES TOP TO BOTTOM across the periodic table.
• As you move left to right, each atom add 1 P+, 1 e- and 1 or more No,
so why does the radius get SMALLER rather than LARGER?
• As the number of PROTONS and ELECTRONS INCREASES, the attraction
between them pulls them closer together, making the atoms SMALLER.
• At the same time, as you move down a group from top to bottom the
atoms get larger.
• Each new period adds a new layer of space the electron cloud, making it
larger, then as you move left to right the P+ and e- draw each other closer so
the atom gets smaller across the period.
ELECTRONEGATIVITY (Eneg)
• Another trend that can easily be seen in the periodic table is that of
ELECTRONEGATIVITY.
• Simply put, Eneg is a measure of an atom’s ability to chemically bond
(react) with other atoms.
• For Eneg, each atom is assigned a number value from 0 (weakest) to 4
(strongest) .
• The closer to 4, the more aggressively an atom will react with
another.
• Look closely at this table of Eneg values:
Eneg Values
What general conclusions can you draw about
electronegativity?
• In general Eneg:
• 1. INCREASES LEFT TO RIGHT across the periodic table.
• 2. DECREASES TOP TO BOTTOM across the periodic table.
• As you move left to right, the atomic radius gets SMALLER, so atoms
hold on to their electrons more tightly and are more reactive.
• As you move down a group, the atomic radius gets LARGER, so atoms
have a weaker hold on their electrons and are less reactive.
So how do Atomic Radius and Electronegativty
compare?
• As Atomic Radius INCREASES, Electronegativity DECREASES.
• This is called an INVERSE PROPORTION; as one thing goes up, another goes
down.