Location: Ch 7: Properties of Matter

PROPERTIES OF MATTER IN THIS CHAPTER:  Elements Atoms are Recyclable and Small Evidence of Atoms' Existence Molecules Compounds The Atomic Nucleus Electrons in the Atom The Phases of Matter Bonds

Atoms are infinitesimally small. In a gram of water there are at least 10²³ atoms, which is more than the number of the drops in all the lakes, rivers and oceans in the world. In an average person’s lungs there are as many atoms in the air as there are breaths in the atmosphere. Atoms are always moving, continuously powered by energy. In solids, the amount of movement is very little, while atoms move very quickly in a gas. It only takes about six years for somebody’s breath to become evenly mixed in the entire atmosphere. At that point, every person on Earth has inhaled at least one of the atoms that you have exhaled. Atoms cannot be seen in a light microscope because atoms are smaller than the wavelengths of light. In order to see an atom, one must use an electron microscope or a scanning tunnel microscope. Brownian motion is the constant jiggling of atoms resulting from the motion of neighboring atoms and molecules.

Atoms can combine to form larger particles known as molecules. For example, two hydrogen (H₂) atoms can bond with oxygen (O) to form a water molecule (H₂O). Matter that is a gas or a liquid at room temperature is usually made of compound molecules. However, not all matter is made of molecules. Metals and crystalline materials are made of atoms that are not joined as molecules. Atoms can also form in compounds. A compound is a substance that consists of different elements in fixed proportions. The chemical formula of the compound tells the proportions of each element. A compound may or may not be made of molecules. Some compounds are made of atoms arranged in pattern.

Atoms are mostly empty space. However, nearly all the mass is packed into a ball known as the nucleus. Ernest Rutherford discovered the nucleus after he shot alpha particles at some gold foil. He reasoned that this nucleus occupied the center of the atom while most of the atom itself was empty space. He was correct. There is so much empty space inside an atom that if the nucleus was the size of a tennis ball, the atom itself would be as big as a stadium! Nuclei are made of nucleons, which have a mass of 1 amu (Atomic Mass Unit). Nucleons without charge are known as neutrons, and charged nucleons are protons. All nucleons are identical copies of each other. Nucleons are not actual particles; they are made of even tinier quarks, which are held together by gluons. Any atoms with the same number of protons are all of the same element. The number of protons determines the element’s atomic number. However, the same does not work for neutrons. Atoms that have different numbers of neutrons are known a

There are two types of charges: positive and negative. Inside an atom, protons are positively charged, neutrons have no charge and electrons have a negative charge. When the number of electrons equals the number of protons the atom’s net charge is neutral. Any atom with a charge of any kind is called an ion. Since positive and negative charges attract each other, electrons are held in orbit of the nucleus by centripetal force. Covalent bonds are created when two atoms share each other’s electrons to become more perfect (that is, with zero or eight electrons). Ionic bonds form when atoms transfer electrons between themselves. Although there is a lot of empty space in an atom, people do not fall through the floor because the forces of repulsion prevent atoms from caving in on each other under pressure. Another type of bond, the hydrogen bond, is formed when two charged atoms attract each other.

The periodic table is a chart that lists atoms by their atomic number and electron configuration. As you go across, the elements increase in number. As you move down, each element has one more electron energy level filled with electrons. Elements in the same column have similar properties and react in similar ways.

Matter exists in four phases. The three most common are solids, liquids and gases. The fourth phase is known as the plasma phase. Plasma consists of positively charged ions and free electrons. Plasmas exist only at very high temperatures (above 2000°C). Plasma is the predominant form of matter in the universe. Stars and much of the intergalactic matter are in the plasma phase. Fluorescent lights use plasmas as well. In all phases of matter, atoms are always in constant motion. Atoms in solid matter vibrate in a fixed position. If heat energy is applied to the material, the atoms will break loose and wander through the material. Now the substance forms the shape of its container; it is a liquid. If even more heat energy is applied to the liquid, the atoms will break away from each other and the material will form a gas. If an even greater amount of heat is applied (2000°C), electrons will have enough energy to break away from the atom. Thus plasma is formed.

In conclusion, all matter is made from and sustained by energy. All matter consists of tiny building blocks known as atoms. Of these atoms, there are only about 110 distinct types of atoms. Most of these atoms have been recycled through matter for billions of years. They are much too small to be seen with visible light but they can be photographed with an electron or scanning-tunnel microscope. A compound is a substance made of different elements combined in a fixed proportion. Some compounds are made of molecules in any particular arrangement while others have atoms arranged in a regular pattern. Atoms are mostly empty space. The mass of an atom is almost entirely in the nucleus, which is made up of neutrons and protons. The number of protons determines the atom’s atomic number. There are two charges, positive and negative. A neutral atom has the same number of protons as electrons. Lastly, the periodic table is a chart of elements arranged according to similar structure and similar properties

Location: Ch 7: Properties of Matter