Most of the substances you interact with in every day life are compounds of different elements. The chemical properties of an element do not change, even if you divide the element down to a single atom. Wood is a compound made mostly from the elements carbon, nitrogen, and hydrogen. The air you breathe is a mixture of nitrogen, oxygen, and carbon dioxide. Even carbon dioxide is a compound, built from the elements carbon and oxygen. The smallest piece of an element you can have, that still has the chemical properties of the element, is an atom.
Cl = chlorine
Use the periodic table of elements to organize the eight elements listed above from the smallest atom to the largest atom.
Atoms are made of three types of subatomic particles, protons, neutrons, and electrons. Each of these particles is actually made up of even smaller particles, called quarks, but that is beyond the scope of this course. Protons and neutrons form the nucleus of an atom (atomic nucleus), and the electrons form a cloud as they move around the nucleus. Keep in mind that the atoms pictured here are not drawn to scale. Most of an atom is empty space between the nucleus and the outer electrons.
Protons have a positive electric charge. The number of protons in the nucleus of an atom determines the identity of that element. An atom of carbon always has six protons. If there is any different number of protons in the nucleus, then the atom is not carbon. An atom of nitrogen has seven protons in its nucleus, an atom of oxygen has eight protons in its nucleus, and an atom of hydrogen just has one proton in its nucleus. The elements of the periodic table are listed in the order of protons found in the nucleus of each atom. Hydrogen is the first element listed with just one proton, helium (He) is the second with two protons, lithium (Li) is the third with three protons, etc.
Neutrons have no electric charge (they are neutral). The numbers of neutrons in the nucleus do not change the identity of an atom, but they do change the mass. Atoms of carbon usually have six
protons and six neutrons in the nucleus, but sometimes there are six protons and eight neutrons. This second element is still carbon (there are six protons), but it is an isotope of carbon called carbon-14. Isotopes are just versions of an element with a different number of neutrons. Some isotopes are unstable and emit radiation.
Electrons have a negative electric charge equal in magnitude to the positive electric charge carried by protons. However, electrons are tiny compared to protons and neutrons, so electrons do not have an important effect on the mass of an atom.
If an atom has an equal number of protons and electrons, then the atom has no overall charge – it is electrically neutral.
If you add electrons to an atom, so that there are more electrons than protons, then the atom has a negative electric charge.
If you remove electrons from an atom, so that there are fewer electrons than protons, then the atom has a positive electric charge.
If an atom has any sort of charge (positive or negative), then the atom is called an ion. Sodium, potassium, calcium, and hydrogen are some ions that play an important role in physiology. (Note: molecules can be ions too.)
If an atom has 11 protons and 10 electrons, then it has an electric charge of +1.
If an atom has 17 protons and 16 electrons, then it has an electric charge of _______.
If an atom has 20 protons and 18 electrons, then it has an electric charge of _______.
If an atom has 6 protons and 6 electrons, then it has an electric charge of _______.
The atoms of helium used to fill balloons each have two protons, two neutrons, and two electrons. Draw a simple picture of a helium atom. Be sure to label the protons, neutrons, electrons, and nucleus. On your drawing, make a note of the charge associated with the protons, the charge associated with the electrons, and the charge associated with the neutrons.
What is the overall charge of a helium atom?
If it was possible to remove one proton from a helium atom, what atom would you have then?