Introduction to Atoms Key terms are: nucleus, proton, neutron, electron, atomic number, isotope, mass number, model.
The Structure of an Atom---is the atoms the smallest part of matter? Atoms are made of even smaller particles called protons, neutrons, and electrons. Protons are + charge Neutrons are 0 charge (neutral in other words) Electrons are - charge
Atoms were the smallest parts of matter--- ALL matter until 100 years ago.... This is when scientist discovered that the three smaller parts existed as parts of the atom. The proton and neutron make up the nucleus of the atom and are in the center of the atom. The electrons move rapidly around the nucleus.
If all these charges exist, what charge does an atom have? If there are 6 positive charge and 6 negative charges... That would result in a balance. Therefore, the atom would be have a neutral charge because all charges balance each other out..... Right? YES!!!
So---do you think all atoms are neutral? Nope! If an atom loses an electron---then that atom would have more positive charges than negative. That would give the atom a + charge. There may also be cases where the atom gains an electron.. that would make more - than + charges and the atom would be - charged. Hopefully all that makes sense now.
So what about the neutron particle then? The neutron has a 0 or neutral charge. It does not affect the charge of the atom. But it is important to the atom...how?!?!?! Look: The primary role of the neutrons in the nucleus of an atom is to contribute to the binding energy or nuclear glue that holds the nucleus itself together. So... Now you know it exists for a purpose. It also helps to balance all those negatives and positive---like between all those + in the nucleus that would naturally repel each other.
How about more on the electrons? They are the smallest part of the three. They have high energy and are buzzing very quickly around the nucleus in a sphere-shaped region that looks somewhat like a cloud. The higher the energy, the farther away from the nucleus is the movement.
So----where are the electrons? It is like the electrons make up MOST of the volume of the atom. If the nucleus was expanded to the size of a marble, the outer edge of the atom would be nearly a football field away.
So.. Although electrons occupy most of the atom s volume, they don t account for much of it s mass. It takes almost 2,000 electrons to equal the mass of just one proton! A proton and neutron are about equal in mass. These two pieces make up most of the mass of an atom. Atoms are so small that scientist measure them in units known as atomic mass units (amu). An example for you to better understand: A proton or a neutron has a mass equal to about one amu. The mass of an electron is about 1/2000 th amu.
Did we always think this way about atoms? NO, the first model came about in 1808 by John Dalton. He thought all elements were made of atoms that were all alike. He thought they looked like tiny, solid, spheres:
By 1897, J. J. Thomson and Lord Kelvin (yes the man for whom the SI temperature unit was named)proposed a new model. This was called the pudding model.
By 1904, we had another model: This was from Hantaro Nagaoka, a Japanese physicist:
1911 we had the Rutherford Model: Ernest Rutherford said the atom was mostly empty space.
On to 1913 with the Bohr Model Niels Bohr proposed this model that showed electrons moving in specific layers or shells. He claimed that the atoms absorb or give off energy when the electrons move from one shell to another.
1932 Chadwick Model James Chadwick, a British scientist, discovered the neutron!! This discovery explained why atoms were heavier than the total mass of protons and electrons.
Present day Modern Model This model includes the work done from the 1920 s to the present. Electrons form a negatively charged cloud around the nucleus. It is impossible to determine exactly where an electron is at any given time.
What is the atomic number? This is the number of protons contained in the nucleus of the atom. Each element of the periodic table has a definite number of protons... Change the proton number and you basically change the element. All carbons atoms have 6 protons in their nucleus even though there are isotopes of the carbon atom. What is an ISOTOPE? This is an atom with the same number of protons but the atoms will have a different number of neutrons in it s nucleus. Look below to see the difference.
Why do we make models of atoms? Scientist make models of atoms because we cannot see the atom---even with an electron microscope, the details are missing. Remember that models are not perfect. They are the best information we have thus far. Complete your vocabulary words.