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Atomics Structure refers to the structure of atoms. How are they built? What are the parts of the atom? Where do they reside? What do they do? There are many models over thousands of years that attempt to show us how atoms are put together.
The best atomic model for middle school students is the Bohr model.
Atomic structure of Helium
Overview: Atoms are the building blocks of matter. They are the smallest part of an element. "Atomos" means uncuttable in Greek.
Atoms are made up of three main parts: protons, neutrons, and electrons. The protons and neutrons are found in the center of the atom, called the nucleus. The electrons are found outside the nucleus, moving around in shells.
Democritus
Democritus
Democritus
Democritus was a Greek philosopher born in Abdera, Thrace, around 460 BC.
Democritus stated that all matter is made up of atoms. These atoms were indestructible and always in motion.
Democritus believed that everything, including people, is made up of tiny particles called atomos, which means "uncuttables" in Greek.
According to him, these little atoms are the building blocks of everything we can observe.
Although Democritus was correct, most people believed what Aristotle thought: Matter was made of Earth, Air, Water and Fire.
He also discovered that a that a cone's volume is equal to 1/3 of a cylinder that had the same base and height.
John Dalton 1808
John Dalton 1808
He said that all matter is composed of atoms which cannot be created or destroyed. All atoms of the same element are identical. For instance, gold atoms make up gold. Oxygen atoms make up oxygen.
Different elements can combine in definite ratios to form compounds. For instance, two hydrogen atoms and one oxygen atom can bond together to form water.
Atoms are rearranged during chemical reactions forming new compounds. He discovered the relative weights of different elements.
John Dalton
JJ Thomson 1897
JJ Thomson 1897
JJ Thomson used a cathode ray tube as well as magnets to discover the electron. Since atoms are electrically neutral, he thought that atoms must have positive and negative charges throughout.
He proposed the plum pudding model. Think of chocolate chip cookie dough. In this model, the plums (or chips) represent negatively charged electrons that can be plucked out of the atom, leaving behind some positively charged pudding ( the dough).
Ernest Rutherford - 1911
Ernest Rutherford - 1911
THE ATOM IS MOSTLY OPEN SPACE!
The Nucleus: In 1911, Ernest Rutherford shot alpha particles (positive in charge) through gold foil. Most of the particles passed through the foil but occasionally, some ricocheted in different directions.
Rutherford concluded that the atom was mostly open space but that it had a dense positive core which we call the "nucleus." If the nucleus were 2 cm in diameter, the nearest nucleus of an adjacent atom would be 400 meters away. Thus lead is empty space at the atomic level!
James Chadwick
James Chadwick
James Chadwick
In 1932, James Chadwick discovered a previously unknown particle in the atomic nucleus. This subatomic particle is known as the neutron because of its lack of electric charge.
This subatomic particle helps to keep the nucleus of an atom together. Neutrons stabilize the nucleus. It sort of acts like glue and it keeps the positive charges of the nucleus together.
Rutherford-Bohr Model of the Atom
Rutherford-Bohr Model of the Atom
In 1913 Niels Bohr and Ernest Rutherford proposed a model of the atom where electrons travel in shells around the nucleus. Electrons can move from one orbit to another by emitting or absorbing energy.
Niels Bohr
Ernest Rutherford
Subatomic Particles
Subatomic Particles
Atomic structure of Helium
Subatomic Particles: Protons, neutrons and electrons are subatomic particles. In other words, they are particles that are smaller than the atom.
Subatomic Particles: Protons, neutrons and electrons are subatomic particles. In other words, they are particles that are smaller than the atom.
Atomic structure of Helium
Protons, found in the nucleus, are positive. Protons determine what atom is.
For example, atoms with 2 protons in the nucleus are Helium atoms. Atoms with 6 protons in the nucleus are Carbon atoms.
Atomic structure of Aluminum
Electrons are negative and fly around the outside of the atom in shells. Electrons bond one atom to another. They are involved in chemical reactions. They have hardly any mass. In fact, the mass of 1 proton = the mass of 1837 electrons.
Atomic structure of Helium
Neutrons are neutral and hold the nucleus together; they are like glue. Neutrons are slightly heavier than protons.
Shells: 2, 8, 8
Shells: 2, 8, 8
2 electrons fill the first level, ring, or shell. How many electrons can hydrogen hold?
8 electrons fill the second level, ring, or shell.
8 fill the third. (Actually, 18 electrons will fill it. However, you will not see this until high school.)
Here are a few examples of the rings of atoms:
Hydrogen
Hydrogen
Helium
Helium
Lithium
Lithium
The number of valence electrons is not responsible for identifying atoms because electrons readily come and go. When it comes to bonding, valence electrons are the ones that matter.
Calculating The Number of Neutrons
Calculating The Number of Neutrons
To determine the number of neutrons in an element, simply subtract the number of protons from the atomic mass.
Isotopes
Isotopes
2 atoms with the same number of protons, but different numbers of neutrons are called isotopes. The atoms differ only in mass. Isotopes are used in the medical field:
Technetium 99- injected in body and scanned.
Cobalt 60 is used for treating cancer.
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