The Greek philosopher Democritus (460 B. C. – 370 B. C.) was among the first to suggest the existence of atoms



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The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos”)

  • The Greek philosopher Democritus (460 B.C. – 370 B.C.) was among the first to suggest the existence of atoms (from the Greek word “atomos”)

    • He believed that atoms were indivisible and indestructible
    • His ideas did agree with later scientific theory, but did not explain chemical behavior, and was not based on the scientific method – but just philosophy












One change to Dalton’s atomic theory is that atoms are divisible into subatomic particles:

  • One change to Dalton’s atomic theory is that atoms are divisible into subatomic particles:

    • Electrons
    • Protons
    • Neutrons












Based on his experimental evidence:

  • Based on his experimental evidence:

    • The atom is mostly empty space
    • All the positive charge, and almost all the mass is concentrated in a small area in the center. He called this a “nucleus
    • The nucleus is composed of protons and neutrons (Discovered by Chadwick)
    • The electrons distributed around the nucleus, and occupy most of the volume
    • His model was called a “nuclear model


OBJECTIVES:

  • OBJECTIVES:

    • Explain what makes elements and isotopes different from each other.


OBJECTIVES:

  • OBJECTIVES:

    • Calculate the number of neutrons in an atom.


OBJECTIVES:

  • OBJECTIVES:

    • Calculate the atomic mass of an element.


OBJECTIVES:

  • OBJECTIVES:

    • Explain why chemists use the periodic table.


1. Draw and name the 4 atomic models.

  • 1. Draw and name the 4 atomic models.

  • 2. Draw an atom with all of the subatomic particles labeled.

  • 3. Convert 29837 to scientific notation.



Atoms are composed of identical protons, neutrons, and electrons

  • Atoms are composed of identical protons, neutrons, and electrons

    • How then are atoms of one element different from another element?
  • Elements are different because they contain different numbers of PROTONS

  • The “atomic number” of an element is the number of protons in the nucleus

  • # protons in an atom = # electrons







Contain the symbol of the element, the mass number and the atomic number.

  • Contain the symbol of the element, the mass number and the atomic number.











Dalton was wrong about all elements of the same type being identical

  • Dalton was wrong about all elements of the same type being identical

  • Atoms of the same element can have different numbers of neutrons.

  • Thus, different mass numbers.

  • These are called isotopes.



  • Frederick Soddy (1877-1956) proposed the idea of isotopes in 1912

  • Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.

  • Soddy won the Nobel Prize in Chemistry in 1921 for his work with isotopes and radioactive materials.



We can also put the mass number after the name of the element:

  • We can also put the mass number after the name of the element:

    • carbon-12
    • carbon-14
    • uranium-235






How heavy is an atom of oxygen?

  • How heavy is an atom of oxygen?

    • It depends, because there are different kinds of oxygen atoms.
  • We are more concerned with the average atomic mass.

  • This is based on the abundance (percentage) of each variety of that element in nature.

    • We don’t use grams for this mass because the numbers would be too small.


Instead of grams, the unit we use is the Atomic Mass Unit (amu)

  • Instead of grams, the unit we use is the Atomic Mass Unit (amu)

  • It is defined as one-twelfth the mass of a carbon-12 atom.

    • Carbon-12 chosen because of its isotope purity.
  • Each isotope has its own atomic mass, thus we determine the average from percent abundance.



Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results.

  • Multiply the atomic mass of each isotope by it’s abundance (expressed as a decimal), then add the results.

  • If not told otherwise, the mass of the isotope is expressed in atomic mass units (amu)









OBJECTIVES

  • OBJECTIVES

    • Describe the origin of the periodic table
    • Identify the position of groups, periods and the transition metals in the periodic table


Dmitri Mendeleev (1834 – 1907)

  • Dmitri Mendeleev (1834 – 1907)

  • Listed the elements in columns in order of increasing mass

  • Then he arranged the columns so that the elements with the most similar properties were side by side



Periodic Table – an arrangement of the elements according to similarities in properties

  • Periodic Table – an arrangement of the elements according to similarities in properties



Henry Moseley (1913)

  • Henry Moseley (1913)

  • Determined atomic number of the atoms of elements



Period – Horizontal rows of the periodic table – (side to side)

  • Period – Horizontal rows of the periodic table – (side to side)

  • There are 7 periods

  • Periodic law – When the elements are arranged in order of increasing atomic number, there is a periodic repetition of their physical and chemical properties



Group – vertical (up and down) column of elements in the periodic table

  • Group – vertical (up and down) column of elements in the periodic table

  • The elements in any group of the periodic table have similar physical and chemical properties

  • Each group is identified by a number and letter A or B

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



These elements can be divided into three broad classes

  • These elements can be divided into three broad classes

  • Metals

  • Characteristics

  • High electrical conductivity

  • High luster when clean

  • Ductile (able to be drawn into wire)

  • Malleable (able to be beaten into sheets)



With the exception of hydrogen all the representative elements on the left side of the periodic table are metals

  • With the exception of hydrogen all the representative elements on the left side of the periodic table are metals

  • Group 1A – alkali metals

  • Group 2A – alkalaine earth metals

  • Most of the remaining elements that are not in Group A are also metals

  • Transition metals

  • Inner transition metals



Rare Earth metals – the inner transition metals which appear below the main body of the periodic table

  • Rare Earth metals – the inner transition metals which appear below the main body of the periodic table



Occupy the upper-right corner of the periodic table

  • Occupy the upper-right corner of the periodic table

  • Non-metals are elements that are generally non lustrous and poor conductors of electricity

  • Many are gases @ room temperature

  • Ex.) O, Cl

  • Others are brittle solids

  • Ex.) sulfur



Group 7A = Halogens ex.) Cl, Br

  • Group 7A = Halogens ex.) Cl, Br

  • Group 8A = Noble Gases “inert gases” - undergo few chemical changes



border the line between metals and non metals

  • border the line between metals and non metals

  • Have properties in between metals and non metals



Rather than memorizing more than 100 elements you need to only learn the general behavior and trends within the major groups

  • Rather than memorizing more than 100 elements you need to only learn the general behavior and trends within the major groups

  • This gives you a working knowledge of the properties of most elements





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