Matter, Atoms, and Bonds

Matter and Elements

Most matter is made of atoms, and only one kind of atom makes an element.
Matter is any substance that occupies space and has mass. Everything, both living and nonliving, is made of matter. Mass is the amount of matter in an object. For example, the Earth's mass is 5.972 x 1024 kg. Matter exists in many forms, and each form has unique characteristics. On Earth, these forms are classified as either a solid, a liquid, or a gas. The states of matter are made of the same particles, but the particles behave differently in each state depending on their energy. The particles in a solid form a regular pattern, giving the substance a fixed shape and volume. Solids cannot easily be compressed. Particles in a liquid do not form a regular pattern, but instead move freely past each other. Liquids have a definite volume but no definite shape; instead, they take the shape of their container. Liquids can be compressed somewhat. Particles in a gas are loosely spaced and do not form regular patterns. They move freely past each other at high speeds. Gases have no definite shape or volume and will fill their container to capacity. Gases are readily compressible.
Matter has mass and occupies space. Matter is usually found in the form of solids, liquids, or gases. Each of these states of matter has unique properties due to the energy of the particles.
An element is a substance that cannot be broken down into simpler substances by chemical reactions. Scientists have identified 118 elements, but only 92 elements occur naturally on Earth. The remaining elements are unstable and made in a laboratory. Each element is identified on the periodic table by a one- or two-letter symbol called a chemical symbol. About 25 naturally-occurring elements are essential to living things. Four of them are common in living things: carbon (C), oxygen (O), nitrogen (N), and hydrogen (H). Elements present in living things in small amounts are called trace elements. Some trace elements in the human body include copper (Cu) and zinc (Zn).
An element's chemical symbol includes its atomic number, its atomic symbol, and its atomic mass. Atomic number is the number of protons in the nucleus. The atomic symbol is its abbreviation as used in chemical formulas. Atomic mass is the average mass of atoms of that element.