Chemistry Study Guide for McGraw-Hill's ASVAB
Everything is made up of matter. Matter is anything that takes up space and has energy. Energy causes change. Matter can exist as a solid, liquid, or gas- the three states of matter. An atom is the smallest building block of matter. Atoms are made of neutrons (with no electric charge), protons (with a positive electric charge), and electrons (with a negative electric charge). The center of an atom is the nucleus. The nucleus contains protons and neutrons. The nucleus of an atom is tiny in comparison to the atom itself. Electrons fly around the nucleus in orbits. Most of an atom is empty space. Energy holds the atom together. Atoms have the same number of electrons and protons, making them stable.
If a substance is made up entirely of the same kind of atom, it is called an element. An element cannot be broken down into a simpler form. The element carbon is made up of only carbon atoms, and the element sulfur is made up of only sulfur atoms.
Scientists have given all elements a one- or two-letter symbol. For example, oxygen is O, sulfur is S, calcium is Ca, and magnesium is Mg. All elements are arranged in a periodic table according to their similarities, providing important information about each element. You will not need to know the periodic table for the ASVAB test, but you may need to know that each block of the table has certain information.
All elements in the periodic table are ordered by their atomic number. The atomic number is the number of protons in the atom. In an atom with a neutral charge, the number of electrons equals the number of protons. The atomic mass number is equal to the number of protons plus the number of neutrons.
Presence of Elements Most of the human body is made up of water, H2O. Your cells contain about 65 to 90 percent water by weight. As much as 99 percent of the mass of the human body is made up of just six elements: oxygen, carbon, hydrogen, nitrogen, calcium, and phosphorus.
By contrast, Earth's crust is made up of lesser amounts of oxygen, but a lot of silicon and aluminum.
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