Atomic Structure and the Periodic Table

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Atomic Structure and the Periodic Table

• Atomic Models

Democrituss Model

• He was a teacher in the
• 4th Century B.C.

• He believed that all matter was
• composed of small indivisible
• and indestructible particles

- He called these particles atoms
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Daltons Model 1. Elements are composed of tiny
indivisible particles
2. Atoms of the same element are identical

• Atoms of different elements can physically mix
  together or
• chemically combine in simple whole number ratios

• Chemical reactions occur when atoms are
  separated,
• joined, or rearranged

• Atoms of one element never change into atoms of
  another
• element

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J. J. Thompsons Model
- He was an English Physicist

• He passes electric current through gases at low
  pressure
• using a cathode ray

• Negative particles were repelled by negative
  plates and the positive
• were attracted to the negative plates

- He was the first person to discover electrons
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Rutherfords Model
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• He found that the center of an atom is dense
  and has a positive charge

• Most of the atom is made of empty space and in
  that empty space
• there are negative charges (the electrons)

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Bohrs Model
- He found that the nucleus of an atom contains
protons and neutrons

• He also found that the electrons do not move
  about randomly
• outside the nucleus

- He believed that the electrons traveled in
paths he called Orbits
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• The Quantum Mechanical Model

- The atomic model that is accepted today

• Protons and neutrons are still found in the
  nucleus and the
• electrons are outside the nucleus but the
  electrons
• are not found in orbits.

• Electrons occupy a space in which they are free
  to move in called
• an orbital

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Basic Information About Atoms
Atoms are the smallest part of an element that
retains the properties of that element
We can now see atoms using a scanning tunneling
microscope
What are atoms made of?
Protons
- Have a charge of positive one
- Have a mass of 1 amu (atomic mass unit)
- Are located in the nucleus of an atom
Neutrons
- Are neutrally charged
- Have a mass of 1 amu
- Are located in the nucleus
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Electrons
- Have a charge of negative one
- Are located outside of the nucleus in orbitals
- The have a mass of 1/1840 amu
- Are the only particles that can enter and
leave atoms
The nucleus takes up a very small part of the
space in an atom. - If an atom were the size of
a football stadium the nucleus would be the
size of a marble
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Numbers derived from atoms and put on the
periodic table.
Atomic Number (Z) the number of protons in an
atom
- It is this different number of protons that
makes each element different
Mass Number the number of protons added to the
number of neutrons
- The number of electrons is not included
because they are so small
Every atom has a neutral charge because it has an
equal number of protons and electrons.
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Short hand notation for writing the atomic mass
and atomic number
12 13 14
C C C
6 6 6
What is the difference between these three carbon
atoms. Is it a different number of protons,
neutrons, or electrons?
Isotopes atoms that have the same number of
protons but a different number of neutrons
(different mass numbers)
- Isotopes all have the same properties of that
specific element
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Atomic Mass the average of all the masses of
isotopes of an element
- Is not a whole number like the mass of an
individual atom
- Atomic mass is based on the reference isotope
Carbon-12.
Atomic mass ?
Calculate the atomic mass of carbon if 2 of all
carbon is Carbon-14, 6 of all carbon is
Carbon-13, and 92 of all carbon is Carbon-12.
Atomic mass .02 14 amu .06 13 amu .92
12 amu 12.1 amu
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Development of the Periodic Table
Mendeleev Constructed the first periodic table
according to the similarities in each elements
properties
- He arranged them in order of atomic masses

• He left blank spaces in his periodic table
  because there were
• no known elements with the appropriate properties
  and masses.

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Later Mosley rearranged the periodic table by
atomic number
The Modern Periodic Table
Periodic Law When elements are arranged in
order of atomic number, there is a repetition of
their physical and chemical properties
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Groups or Families vertical columns. Group
numbers are indicated with a number and a
letter A or B
- Elements within a group have similar physical
and chemical properties

• Group A elements are the representative
  elements
• because they exhibit a wide range of chemical
• and physical properties

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Where are things located on the
Periodic Table?
? Nonmetals
Metals ?
The light blue elements are semimetals
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Properties of Metals
- They make up 80 of the elements
- All metals except for one is a solid at room
temperature

• One the big periodic table solids are black,
  liquids are
• blue, and gases are red

- They have a metallic luster
- They are good conductors of electricity
- They are malleable
- They are ductile
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Properties of Nonmetals
- They lack luster
- They are brittle
- They are poor conductors of electricity
(insulators)
Properties of Semimetals

• They have some of the characteristics of metals
  and some of
• nonmetals