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Democritus was a Greek philosopher (470-380 B.C) father of modern atomic. Term of atom.
Dalton - 1803
- First that created atomic theory.
THEORY:
1) Atoms are tiny, indivisible particles.
2) Atoms of one element are all the same.
3) Atoms of different elements are different.
4) Compounds form by combining atoms.
Thomson - 1904
- Discovered electrons.
- Atoms are composed of electron
troughout of a cloud of positive charge.
Rutherford - 1911
- Positive charge in the center: The NUCLEUS
- Discover protons.
- Experiment with gold foil (particles (+) went through).
Borh - 1913
- Improved Rutherford's model.
- Electrons move around the nucleus in orbits (specific layer) of fixed sizes and energy.
Schrodinger - 1926
- Electrons dont move in paths around the nucleus, but in WAVE.
- There is a "cloud of probability", called orbitals, which electrons are found.
1932
- Discovered neutrons.
- Neutrons are also found in the nucleus.
Planetary Model
Protons and neutros are held tighly together at the center in a tiny, dense region called the NUCLEUS.
Electrons exist in the region around the nucleus in regular patterns called the
*Energy Levels/ Energy Shells
ATOM
ATOM
Neutral ATOM
Remember how a unit of electric charges can be defined????????
- Each proton has an electrical charge of ________.
- Each neutron has an electrical charge of ________.
- Each electron has an electrical charge of ________.
Recall that atoms are neutral (have an overall charge of zero.) This means that:
Number of protons = Number of electrons
EXAMPLES
Example 1:
C Carbon ATOM: 6 protons, 6 electrons
Example 2:
N Nitrogen ATOM: 7 protons, 7 electrons
Unit is defined as:
MASS OF 1 ATOM
A neutron has the same mass as a proton.
The mass of the atom comes mostly from the protons and neutrons in the nucleus.
The mass of the electrons is so small compared to the mass of the protons and neutrons it can be ignored.
Therefore: The atomic mass (or mass number) of an atom = NUMBER OF PROTONS + NUMBER OF NEUTRONS.
Why is the atomic mass an averaged decimal????
Because while atoms of the same element have the same number of PROTONS, they can differ in the number of neutrons.
This alters the mass of the atom.
Atoms that have the same number of protons but different number of neutrons, are called ISOTOPES of the same element.
C and C are isotopes found in nature. They both have 6 protons but C (with an atomic mass of 13 amu) has ___ neutrons while C (with an atomic mass of 12 amu) has ____ neutrons.
In nature, C is found as 99% and 1 % C. So the average atomic mass of the element C is calculated from that information to get a value of __________.
ATOMIC NUMBER= # of protons = # of electrons.
ATOMIC MASS= # of protons + # of neutrons.
This means:
- The number of neutrons
= Atomic mass- # of protons
= Atomic mass - atomic number
Oxygen Symbol:
Atomic Number:
Atomic Mass:
Protons:
Neutrons:
Electrons:
Lithium Symbol:
Atomic Number:
Atomic Mass:
Protons:
Neutrons:
Electrons:
What information can you find in the periodic table?
- Period, group (1-18 or I-VIII) (family).
- Is organized in (3):
- The elements are arranged by increasing atomic number.