Transcript valence electron

GROUPS/FAMILIES &
VALENCE ELECTRONS
CHAPTER 5.3
Elements in a period have
the same number of electron
shells or energy levels.
Elements in a group or
“family” have similar
properties.
VALENCE ELECTRONS
• Why do the elements in a group have similar
properties?
VALENCE ELECTRONS
• Why do the elements in a group have similar
properties?
• They have the same number of valence
electrons.
• The properties are not identical because the
valence electrons are in different energy
levels.
• A valence electron is an electron that is in the
highest occupied energy level of an atom.
• Outer most electron shell
Electrons Filling shells as atomic # increases
(# of electrons goes up as # of protons goes up):
H
1
1
Atomic #
Valence e’s
Atomic #
Valence e’s
He
2
2
C
N
6
4
7
5
Li
1st shell now 3
full, start 2nd 1
Ne

10 2nd shell now
8 full, start 3rd
Be
4
2
Na
11
1
B
5
3
e capacity:
1st shell = 2
2nd shell = 8
3rd shell = 8
4th shell = 18
5th shell = 18
6th shell = 32
7th shell = 32
VALENCE ELECTRONS
• How do we determine the number of valence electrons?
• When groups in the periodic table are labeled as Series A
and Series B:
• For Series A (Groups 1A - 8A):
• group number = the number
of valence electrons for an
element in that group.
• Valence electrons play a key role in chemical reactions.
• Properties vary across a period because the number of
valence electrons increases from left to right.
OCTET RULE
• Atoms are most stable if their outer most electron
shell is filled or empty.
• Filled shell contains 8 electrons (octet)
• Except for H and He (atomic #1 & #2)
• Atoms gain, lose, or share valence electrons in
order to fill or empty their outer shell
• Atoms gain, lose, or share electrons based on what is
easiest.
OCTET RULE
• Na has 11 protons and 11 electrons.
• Period 3 = 3 e- shells
• Group 1A = 1 Valance eNa
• 2 e- in 1st shell (full)
• 8 e- in 2nd shell (full)
• 1 e- in 3rd shell (valence)
proton charge (11 x +1)
= +11
+ electron charge (11 x -1)
= -11
net charge
= 0 (neutral)
OCTET RULE
• When atoms lose or gain valence electrons  no longer neutral
• Na has 1 valence e- -- easier to lose 1 than gain 7 to fulfill octet rule
• leaves only 10 electrons
• (2 e -
in 1st shell; 8 e- in 2nd shell; 1 e- in 3rd shell) 
• (2 e- in 1st shell; 8 e- in 2nd shell; no e- in 3rd shell)
(11 x +1)
+ (10 x -1)
= 1+
• Example: Cl has 7 valence e- -- easier to gain 1 than lose 7
• (2 e- in 1st shell; 8 e- in 2nd shell; 7 e- in 3rd shell) 
• (2 e- in 1st shell; 8 e- in 2nd shell; 8 e- in 3rd shell)
(17 x +1)
+ (18 x -1)
= 1-
Properties
GROUPS/FAMILIES
GROUP 1A – ALKALI METALS
• 1 Valence Electron.
• Soft & Silvery
• Extremely Reactive (Most reactive Metals)
• Found in nature only in compounds.
• NOT found free in nature
• Mix well with water
• The reactivity of alkali metals increases from the top of
Group 1A to the bottom.
GROUP 1A – ALKALI METALS
Unlike most metals
Sodium is soft enough
to cut with a knife.
Sodium reacts violently
with water and releases
enough energy to ignite
the hydrogen gas that is
produced.
GROUP 1A – ALKALI METALS
• Potassium (& Sodium)
• Stored under oil to keep them from
reacting with the oxygen and water
vapor in air.
• Cesium
• So reactive that it is usually stored
in a sealed glass tube containing
argon gas.
• Why argon?
GROUP 2A – ALKALINE EARTH METALS
• 2 Valence Electrons
• Similar to Alkali Metals
• Harder than metals in Group 1A
• Higher melting points
• The melting point of
magnesium is 650°C;
sodium 98°C
• Almost as reactive as Alkali metals
• NOT found free in nature
• Reactivity increases
• From top to bottom
GROUP 2A – ALKALINE EARTH METALS
• Differences in reactivity among the alkaline earth
metals are shown by the ways they react with water.
• No reaction occurs when beryllium is added to water.
• Magnesium will react with hot water but not cold
water.
• Calcium, strontium, and barium react easily with cold
water.
•Magnesium
• Photosynthesis: Chlorophyll
• Creates alloys stronger yet lighter than steel
•Calcium
• Oyster shell and a pearl - calcium carbonate (Ca, C, & O).
• Also found in toothpaste
Oyster shell with pearl
• Plaster cast - calcium sulfate.
Spinach plant
GROUP 3A – THE BORON FAMILY
• 3 Valence Electrons
• Most are metals
• Well-known metal – Al (aluminum)
• Less familiar metals - Ga (gallium), In (indium), and
Tl (thallium).
• Boron is a metalloid
GROUP 3A – THE BORON FAMILY
• Aluminum
• Most abundant metal in Earth’s crust.
• Less reactive than Na and Mg
• Strong, lightweight, and malleable.
• Good conductor of electric current.
• Boron
• B, Si, & O form a compound used to make glass that does not
shatter due to rapid temperature change.
• laboratory glassware
• cookware that can go directly from the oven to the refrigerator.
GROUP 4A – THE CARBON FAMILY
• 4 Valence electrons
• Family Contains
• 1 Nonmetal - C (carbon)
• 2 metalloids - Si (silicon) & Ge (germanium)
• 2 metals - Sn (Tin) & Pb (Lead)
• Notice that the metallic nature of the elements increases
from top to bottom within the group. Germanium is a better
conductor of electric current than silicon.
GROUP 4A – THE CARBON FAMILY
• Silicon
• Carbon
• Except for water, most of the
compounds in your body
contain carbon.
• Life on Earth would not exist
without carbon.
• Reactions that occur in
the cells of your body are
controlled by carbon
compounds
• 2nd most abundant element in Earth’s crust.
• The clay used to produce pottery contains silicon
compounds called silicates.
GROUP 5A – THE NITROGEN FAMILY
• 5 Valence electrons
• Can share electrons to form compounds
• Family Contains:
• 2 nonmetals - N (nitrogen) & P (phosphorus)
• 2 metalloids - As (arsenic) & Sb (antimony)
• 1 metal - Bi (bismuth).
• Group 5A includes elements with a wide range of physical
properties.
• Nitrogen is a gas
• Phosphorus is a solid nonmetal
• Bismuth is a dense metal.
GROUP 5A – THE NITROGEN FAMILY
• When air is cooled - O condenses before the N due to its lower
boiling point
• Much of the N obtained from air is used to produce
fertilizers.
• The numbers on the bags of fertilizer are, from left to right, the
relative amounts of nitrogen, phosphorus, and potassium.
GROUP 6A – THE OXYGEN FAMILY
• 6 Valence electrons
• Family Contains:
• 3 nonmetals - O (oxygen), S (sulfur), & Se
(selenium)
• 2 metalloids - Te (tellurium) & Po (polonium)
• Reactive
GROUP 6A – THE OXYGEN FAMILY
• Oxygen
• Most abundant element in
Earth’s crust.
• Complex life forms need O to
stay alive because O is used to
release the energy stored in food.
• Ozone (O3) is another form of the element oxygen.
• Sulfur
• One of the first elements to be discovered because it is found in
large natural deposits.
GROUP 7A – HALOGENS
• 7 Valence electrons
• All Nonmetals
• At room temperature:
• chlorine is a gas,
• bromine is a liquid
• iodine is a solid.
• MOST Reactive of the nonmetals
• Often find these elements bonded with elements
from Group 1A
GROUP 7A – HALOGENS
• Despite their physical differences, the halogens have
similar chemical properties.
• React easily with most metals.
• Image:
• Chlorine reacting with steel wool 
GROUP 8A – THE NOBLE GASES
 8 Valence electrons = Full Shell – Octet Rule
 Helium (He) has only 2 valence electrons = Full
 All Non-metals
 Extremely Unreactive
 Colorless and odorless
GROUP 8A – THE NOBLE GASES
• When electric current passes
through noble gases, they emit
different colors.
• He (Helium) emits pink,
• Ne (Neon) emits orange-red,
• Ar (Argon) emits lavender,
• Kr (Krypton) emits white
• Xe (Xenon) emits blue.
ASSESSMENT QUESTION
1. Why do elements in a group have similar chemical
properties?
a. They have the same number of valence electrons.
b. They have the same ratio of protons to neutrons.
c. Their atomic masses are multiples of the least
massive element of the group.
d. They have the same number of total electrons.
ASSESSMENT QUESTION
1. Why do elements in a group have similar chemical
properties?
a. They have the same number of valence electrons.
b. They have the same ratio of protons to neutrons.
c. Their atomic masses are multiples of the least
massive element of the group.
d. They have the same number of total electrons.
ASSESSMENT QUESTION
2. Which Group 2A element would you expect to
react most readily with water?
a. beryllium (Be)
b. calcium (Ca)
c. barium (Ba)
d. radium (Ra)
ASSESSMENT QUESTION
2. Which Group 2A element would you expect to
react most readily with water?
a. beryllium (Be)
b. calcium (Ca)
c. barium (Ba)
d. radium (Ra)
ASSESSMENT QUESTION
3. In general, the metallic characteristics of within
a period decreases from left to right.
a. True
b. False
ASSESSMENT QUESTION
3. In general, the metallic characteristics of within
a period decreases from left to right.
a. True
b. False
ASSESSMENT QUESTION
4. Elements of the Nitrogen Family have
a. 4 Valence electrons
b. 6 Valence electrons
c. 5 Valence electrons
d. 7 Valence electrons
ASSESSMENT QUESTION
4. Elements of the Nitrogen Family have
a. 4 Valence electrons
b. 6 Valence electrons
c. 5 Valence electrons
d. 7 Valence electrons
ASSESSMENT QUESTION
5. Atoms are most stable if their outer most electron shell
is filled or empty.
a. True
b. False
ASSESSMENT QUESTION
5. Atoms are least stable if their outer most electron shell
is filled or empty.
a. True
b. False