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Chemistry - Unit 3

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Mark Holcomb

on 3 February 2015

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Transcript of Chemistry - Unit 3

Trends of the Periodic Table
Trend #1 - Atomic Radius
Trend #2 - Ionization Energy
Trend #3 - Electronegativity
Unit 3
Unit 2 Review
Parts of an Atom
Atomic Number
Average Atomic Mass Number
Element Symbol
Element Name
Tells the...
Number of Protons
Number of Electrons
Tells the...
TOTAL number of protons and neutrons
Average mass of the nucleus
The Periodic Table did not always look like this!
It once looked like this!
Mendeleev's Periodic Table
(Organized by Mass Number)
Periodic Table – organization of all the elements
In 1869, Dimitri Mendeleev produced the 1st period table. He put all the elements with similar properties in the same horizontal row according to
Atomic Mass

In 1913, Henry Moseley developed the concept of
Atomic Number
. This fixed a few problems with Mendeleev’s table.

The Periodic Law
– when elements are arranged in order of increasing atomic number, their
properties show a pattern

Elements with similar properties are aligned in
columns called
or families.
rows are called
There are 18
and 7
Elements in a
are similar chemically and physically because they have the same number of valence electrons.
Recall group number and valence electrons from Unit 2.
Elements in a
are only similar in the number of energy levels they have.
1st period has 2 elements.
2nd and 3rd periods have 8 elements.
4th and 5th periods have 18 elements.
6th and 7th periods have up to 32 elements.
Notice the correlation of these numbers to the number of maximum electrons in each shell.

*Notice that the lanthanides actually fit into the 6th period and the actinides in the 7th.
Many properties of the elements change in a predictable way as you move across or down the periodic table.
These trends are general; there may be a few exceptions. The noble gases, because of their stability, don’t follow many of the trends.

Atomic Radius – the distance from the center of the nucleus to the outermost electrons.
Atomic radii are in the tenth of a nanometer range (1x10 m)‏
The trend: Radii increases down the periodic table and decreases across the periodic table.
Atoms get MUCH LARGER going down a group because the addition of energy levels.
Atoms get a LITTLE SMALLER going across a period because even though there are the same number of energy levels, there are more protons in the nucleus causing the electrons to be pulled in tighter.

Notice the Noble Gases do not fit the trend.
How does the size of an atom change when it becomes an ion?

When an atom loses electrons to become a positive ion it becomes MUCH SMALLER because it is losing a whole energy level.

When an atom gains electrons to become a negative ion it becomes a LITTLE LARGER.
Ion Radius
Ionization energy – energy needed to remove an electron from an atom

It's like a measure of how tightly the atom holds its electrons

IE (ionization energy) decreases down the periodic table and increases across the periodic table.

IE increases across because the more valence electrons an atom has the more it wants to keep them (many atoms want to gain, not lose electrons)‏

IE decreases down because larger atoms hold electrons less tightly because the electrons are further away from the nucleus.

IE trend DOES include the noble gases because they are very stable with 8 valence electrons, it takes more energy to take away one from a noble gas than any other element.

Electronegativity – the ability to attract electrons in a chemical bond
Electronegativities (Eneg) are numbers without units
Fluorine has the highest eneg = 4.0
Eneg will be used in the next unit to determine how atoms are bonded...until then...just know the general trend and definition

Eneg decreases down a group and increases across a period.
It does NOT include the Noble Gases!
All elements can be classified as one of these three.
Positive side
Negative side
lie to the left of the stair step line
have luster (shiny)‏
usually solid at room temp. (except Hg)‏
usually silver-colored (except Cu, Au)‏
good conductors of heat and electricity
malleable (able to be hammered into thin sheets)‏
ductile (able to be drawn into wires)
lie to the right of the stair step line
not shiny
solids, liquids, and gases at room temp. (variety)‏
various colors
poor conductors of heat and electricity

Note that Aluminum is NOT a metalloid even though it touches the stair-step line!!!
lie on the stair step line (except Al which IS a metal)‏
Also called “semimetals”
somewhat shiny
not very malleable, but not very brittle
semiconductors (only conduct under certain conditions – very useful in electronics)‏
Alkali Metals (1A)
All metals except H
Hydrogen: H – explosive gas (H bomb)
H O – water
Other Alkali Metals:
Very very reactive with air, water and many other things
Soft enough to be cut with knife
Must be stored under mineral oil for
protection against moisture and air
As ions, Na and K are essential electrolytes in our body
Some common compounds:
NaCl – table salt (sodium chloride)‏
NaClO – bleach
NaHCO – baking soda
Li CO – used to treat manic depression

Alkaline Earth Metals (2A)
Not quite as reactive as alkali metals
MgSO – epsom salts
CaCO – limestone, marble, chalk

Transition Metals (B's)‏
Some used in coins (Ni, Au, Ag, Cu)‏
Fe vital to life because it is part of hemoglobin for oxygen transport
Fe also primary building metal in society (steel)‏
Cr used as protective coating and in alloys because it resists corrosion (stainless steel)‏
W used in incandescent light bulb filaments
Ti is a strong light metal

2 3

Soft, silvery metals
Slightly reactive with air and water so can't be used as structural materials
Little commercial importance

Lanthanides (1st row in f block)
Actinides (2nd row in f block)
ALL of these are radioactive (unstable and emits radiation)‏
Uranium used as fuel in nuclear power plants

The Boron Family (3A)
Most Al found as compounds in clays in earth's crust
Al used in beverage cans, pots,
pans, Al foil
Al is the 2nd most produced and consumed metal after Fe

The Carbon Family (4A)‏
Carbon is the major component of coal,
petroleum, and natural gas (fuels)‏
Forms incredible number of compounds (very versatile)‏
Occurs in all living things
Pure forms are diamond and graphite
Compounds: CO and CO and a zillion more...
SiO (silica) is the principle component of quartz,
sand, rocks, and glass
Used to make transistors and solar cells because it
is a semiconductor
Tin – common metal (roofs, cans)‏
Lead – poisonous metal – previously used in gasoline and paint (“unleaded gasoline” and “did you eat paint chips as a child?”)‏

The Nitrogen Group (5A)‏
N – 78% of atmosphere
NH – ammonia
H PO – phosphoric acid found in colas

The Oxygen Family (6A)‏
Reactive group
O – 20% of atmosphere, required for respiration
O – ozone – protective layer in upper atmosphere
Sulfur – yellow solid, medications
Sulfur gives fools gold its color
Sulfur compounds smell bad (rotten egg)‏

Halogens (7A)
Very reactive group
Cl – green poisonous gas
NaCl – table salt
NaClO – bleach
Iodine – essential nutrient so KI is added to table salt to make it “iodized” since we don't get enough iodine in our regular diet
Fluorine found in toothpaste as fluoride (F )‏

Noble Gases (8A)
INERT – unreactive
Argon – approx. 1% of atmosphere
He – balloons
Liquid helium used as a coolant
Ne – emits bright color when excited (signs)‏

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