Term
Bohr’s Theory of the Atom emission
spectrum |
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Definition
When atoms absorb electrical or heat energy, they can
re-emit the energy as light. Each element emits a very specific pattern of
wavelengths, or colours, of light. This pattern is called the emission
spectrum of the element. |
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Term
| Bohr’s Revisions to the Atomic Theory: Electrons in Specific Orbits |
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Definition
• Electrons are located in defined shells, which are located certain
distances from the nucleus.
• Electrons cannot exist between the defined shells.
• Electrons can gain energy to move up to a higher shell, or they can
lose energy to move down to a lower shell.
• Electrons are more stable (have less energy) when they are closer to
the nucleus. |
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Term
| The Atomic Theory of Matter |
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Definition
There are a maximum number of electrons
that can occupy any one shell. The first shell can only contain a maximum
of two electrons, and the second shell can contain a maximum of eight. The
electrons fill the shells starting with the first or innermost shell and work outward.
For example, an element with six electrons has two electrons in
the first shell and four electrons in the second |
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Term
| The Number of Shells for an Element |
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Definition
The number of shells that an element will need is related to which row of the Periodic Table it is found in.
As you will learn in Chapter 8, it is the arrangement of the electrons that
determines the characteristics and chemical behaviour of an element. |
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Term
| The Atomic Theory of Matter |
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Definition
• All matter is made of atoms.
• Atoms are the smallest pieces of an element.
• Elements combine to form compounds. The atoms in the compound are held together by electrical attractions.
• An atom is composed of a nucleus surrounded by electrons.
• The nucleus is composed of positively charged protons and uncharged neutrons.
• All the atoms of an element have the same unique number of protons.
• All the nucleus contains most of the mass of the atom and all of the
positive charge.
• There is only empty space between the electrons and the nucleus.
• Electrons have a negative charge and very little mass.
• Electrons orbit the nucleus only in specific, allowed shells.
• For the first 20 elements, the first shell contains a maximum of two electrons, the second shell contains a maximum of eight electrons, and the third shell contains a maximum of eight electrons.
• Electrons absorb or emit specific amounts of energy to change shells. |
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Term
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Definition
In 1913, Henry Moseley studied the X-ray
part of the emission spectra of elements, and noted that a characteristic energy peak increased by one unit for each element in order of increasing atomic mass,with a few exceptions.
Thus, the elements could each be given a specific number, called the atomic number.
Scientists now know that the atomic number is the number
of protons in the nucleus.
It is the atomic number (not the atomic mass) that determines the
order of the elements in the modern Periodic Table. |
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Term
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Definition
The Periodic Law can now be stated as: The properties of the elements are a periodic or regularly repeating function of their atomic number.
It is the atomic number (not the atomic mass) that determines the
order of the elements in the modern Periodic Table. |
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Term
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Definition
The total number of protons and neutrons in the nucleus of an atom is
called the mass number. |
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Term
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Definition
The mass number of an element is often written after the element name, as in chlorine-35.
The mass number, along with the
chemical symbol for an element and the atomic number, can also be written
in standard atomic notation.
Like the symbols for the elements,
standard atomic notation allows scientists to communicate and share theirideas efficiently. |
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Term
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Definition
When an atom becomes charged, there are more or fewer electrons than
protons in the atom. A charged atom is called an ion. |
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Term
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Definition
When there are more
electrons than protons, the atom has a negative charge and is called a negative ion.
If there are 3 more electrons than protons,
the ion has a charge of 3-. |
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Term
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Definition
When there are fewer electrons than protons, the atom has a positive charge
and is called a positive ion.
For example, if there are 2 fewer electrons than protons, the ion has a charge of 2+. |
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Term
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Definition
| The charge of an ion, whether positive or negative, is called the ion charge. |
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Term
| standard notation for ions |
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Definition
In standard atomic notation the ion charge is written above and to the right of the symbol.
If the charge is 1 or 1, the “1” is not usually written.
It is important to note that, when an atom becomes charged, the number of protons in the atom does not change.
It is important to note that, when an atom becomes charged, the number of protons in the atom does not change. |
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