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5.1 Atoms are the smallest form of element s
What we should already know:› All matter is made of atoms› Elements are the simplest substances
o What we will learn:o Where atoms are found and how they are
named o About the structure of atomso How ions are formed from atoms
Greek philosophers use to believe that everything on Earth was made up of air, water, fire, and earth or a combination of those substances.
Today’s chemists know here are about 100 basic substances, or elements, which make up everything we see and touch.› Some of these elements appear by
themselves› Some appear in combination with others
Types of Atoms in Earth’s Crust and Living Things:
Hydrogen (H) makes up about 90% of the mass of the universe
Hydrogen (H) makes up only about 1% of the earth’s crust
Look at the graphs on page 138:› Oxygen (O) makes up the majority of both
humans and the earth’s crust› After oxygen (O) there are many differences in
our make-up All living things are composed primarily of:
oxygen (O), carbon (C), hydrogen (H) , and nitrogen (N)
Names and Symbols of Elements:
Each element has its own unique atomic symbol:› Some elements use the first letter of the
name: Oxygen = O Hydrogen = H Sulfur = S› Other elements use the first letter plus
another letter found in the name: Aluminum = Al Platinum = Pt Zinc = Zn
› Some elements use the letters from the Latin word such as: gold = Au Lead = Pb
No matter the letters used, the first letter is always UPPER CASE and the second letter is always lower case
Each element is made of a different atom
John Dalton proposed that each element is made of tiny particles called atoms.
All of the atoms of a particular element are identical but are different from atoms of all other elements.
The Structure of an Atom Atoms contain charged particles which
can be (+) or (-)› Particles with like charges repel each other
(push away from)› Particles with different charges attract
each other (drawn to) Atoms are composed of three types of
particles:› Protons› Neutrons› Electrons
Protons:› Carry a (+) charge› Are found in the nucleus of the atom› Make the element what it is
If you change the number of protons, you change the element
Neutrons:› Carry a neutral charge (no charge)› Are found in the nucleus of the atom› Have about the same mass as a proton
Electrons:› Carry a (-) charge› Are found outside the nucleus of the atom› Determine how elements will bond with
each other
Size and attraction: About 10-10 meter in diameter
› You could fit millions of atoms in the size of the period in your book
Electrons are much smaller than protons and neutrons› About 2000 times smaller
Electrons move about the nucleus very quickly› Impossible to pin point the location at any
time› Stay attracted to the nucleus because of
the (+) protons
Atomic Number:
The atomic number of an atom indicates the number of protons in the nucleus.
You can not change the atomic number of an element and still have that same element
The atomic number of hydrogen (H) will always be 1.
The atomic number of gold (Au) will always be 79.
Atomic mass number
The total number of protons and neutrons in an atom’s nucleus.
Not all atoms have the same number of neutrons:› Chlorine (Cl) has 17 protons but some atoms
have 18 neutrons, others may have 20. When atoms of the same element have a
different number of neutrons they are called isotopes.› To find the number of neutrons you must
subtract the atomic number from the atomic mass number.
Ions: A neutral atom has an equal number of
protons (+) and electrons (-).› The negative charges and the positive
charges balance each other. An ion is formed when an atom loses
or gains one or more electrons.› By gaining or losing electrons, the balance
of (+) and (-) is no longer there.
Positive Ions: When an atom loses one or more
electrons, it takes on a positive charge.› Example: page 142› A neutral atom of sodium contains 11
protons and 11 electrons—the charges balance each other.
11 (+)11 (-)Neutral charge
When the sodium atom loses an electron, there are more (+) charges than (-) giving the ion a + charge
To indicate or write a positive charged atom, you add a + sign to the right side of the atomic symbol.
Na+
If an atom loses more than one electron, you add the number lost to the atomic symbol before the + sign
Na 2+
Negative Ions: Negative ions are formed opposite to
the positive ions—Electrons are added to the atom giving it a negative charge.
When indicating a negative electron, you add a – sign to the top right of the atomic symbol.
Cl- If more than one electron is added, you
write the number with the sign.
Cl2-
5.2: Elements make up the periodic table
Not all atoms of an element have the same atomic mass number (total number of protons and neutrons)
The atomic mass of the atom is the average mass of all the element’s isotopes (same atom-different number of neutrons.)
Mendeleev’s Periodic Table page 146
Early 1800’s, Dmitri Mendeleev wanted to organize the elements based on their physical and chemical properties.
Created the first periodic table by arranging the elements by:› Similarities made up each row› Increase down each column by atomic
mass
Modern periodic table
Page 148-149 in your book Elements are arranged by atomic
number (number of protons) Elements with Similar properties are
arranged in columns
Reading the periodic table
Each square represents an individual element:
Atomic number (number of protons)
Atomic symbol
Name Atomic mass
The color of the letters indicates the physical state of the element at room temperature:› White = gas› Blue = liquid› Black = solid
Your table is also divided by the colors:› Green = Nonmetal› Yellow = Metal› Purple = Metalloid
Groups Each column on the table is known as a
group or family because they appear to be related.
The halogens-group 17 tend to combine well with groups one and two.
Similar chemical properties Different physical properties
GasesLiquidSolids
Periods Each horizontal row is called a period. Properties of the elements change in a
“predictable” way from one end to the other.
Elements on the far left are metals. Elements on the far right are
nonmetals.
What else is on the table?An atom’s size is important because it affects how the atom will react with another atom. What is the pattern in the table for atomic size?
Periodic table densities:
Densities of the elements follows a pattern with the least dense on the left and right and the most dense in the middle.
5.3: The periodic table is a map of the elements
Just like a map of the United States, the periodic table is a map showing:› Metals (left)› Metalloids (middle)› Nonmetals (right)
Nonmetals does not count hydrogen (H) Your book shows these regions in:
› Yellow (metals)› Purple (metalloids)› Green (nonmetals)
Reactive:› Indicates how likely an element is to
undergo a chemical change.› Most elements are somewhat reactive and
combine with other materials› Groups 1 and 17 are the most reactive› Group 18 is the least reactive
Metals: Elements that conduct electricity and
heat well Have shiny appearance Can be shaped easily by pounding,
bending, or being drawn into a long wire
Solids at room temperature except for mercury
Reactive and transition
Reactive metals
Groups 1 and 2 Group 1 is alkali metals
› Very reactive› When exposed to air-rapid reactions occur› Sodium and potassium are stored in oil
Group 2 is alkaline earth metals› Less reactive than alkali metals› More reactive than most other metals› Calcium and magnesium
Transition metals Groups 3-12 Generally less reactive than most other
metals Properties make them useful in
industry and technology Commonly combined to form alloys
such as brass (combination of copper and zinc)
Includes common metals such as copper, gold, silver, and iron
Rare Earth Elements
Top row of the two rows of metals that are usually separated from the rest of the table
AKA: lanthanides Thought to be rare in amount but have
been discovered as more common just hard to isolate in pure form.
Nonmetals Found on the right side Properties are generally the opposite of
the metals and vary more:› Many are gases at room temperature› Some are solids› One is a liquid
Solids are dull and cannot be shaped by hammering or drawn into wires
Generally poor conductors of heat and electricity
Halogens:› Greek meaning “forming salts”› Group 17› Very reactive nonmetals that form
compounds called salts with many metals› Often used to kill harmful microorganisms
Noble Gases:› AKA: inert gases› Group 18› Almost never react with other elements› Examples: neon, krypton, xenon, argon
Metalloids Elements that have properties of both
metals and nonmetals Often make up the semiconductors of
electrical devices› Semiconductors conduct electricity under
some circumstances but not others
Some atoms change their identity
Radioactivity:› Process by which atoms produce energy
and particles› Isotopes (atoms with different numbers of
neutrons) are radioactive if the nucleus has too many or too few neutrons
› When this happens, particles are produced from the nucleus of the atom to restore the balance.
Radioactive Decay Radioactive decay:
› When radioactive atoms produce energy and particles from their nuclei, the identity of the atom changes because the number of protons changes.
› Steady rate of change Half life:
› Amount of time it takes for one-half of the atoms in a particular sample to decay.
› Not affected by temperature or pressure› Specific to each isotope
Half life example:
1000 atoms of kryptonite› Half life of kryptonite is 1 year
After 1 year, you would have ½ or 500 atoms of kryptonite.
After 2 years, you would have ½ of the atoms from year 1 or 250 atoms of kryptonite.
After 3 years, you would have ½ of the atoms from year 2 or 125 atoms of kryptonite.
Scientific notation “short hand” way for scientists to write
extremely large or small numbers. It will always be a number between 1
and 10 and a power of 10. To write 6,400,000,000 in scientific
notation you move your decimal to the left until you end up with 6.4.› Count how many spaces you moved (9)› Re-write the number as 6.4 x 109
To write 0.0000023 in scientific notation:› Count how many spaces you move the
decimal to the right to get to 2.3› 6 spaces› Re-write the number as 2.3 x 10-6
When going to scientific notation:› If you move your decimal to the left, your
exponent is positive› If you move your decimal to the right, your
exponent is negative