{"id":426,"date":"2017-08-23T06:08:40","date_gmt":"2017-08-23T06:08:40","guid":{"rendered":"http:\/\/americanboard.org\/Subjects\/elementary-education\/?page_id=426"},"modified":"2020-12-29T08:03:36","modified_gmt":"2020-12-29T08:03:36","slug":"structure-and-properties-of-matter","status":"publish","type":"page","link":"https:\/\/americanboard.org\/Subjects\/elementary-education\/structure-and-properties-of-matter\/","title":{"rendered":"Structure and Properties of Matter"},"content":{"rendered":"
\n
Workshop Index<\/a>\u00a0Next Lesson \u27a1<\/a><\/div>\n

<\/p>\n

Structure and Properties of Matter<\/h1>\n

Objective<\/h4>\n

In this lesson, we will review the properties of matter, the organization of elements on the periodic table, and the types of chemical bonds. We’ll also review chemical reactions and the properties of chemical solutions.<\/p>\n

\n

It All Matters\u2014and it’s All Matter<\/h3>\n

Chemistry<\/abbr> is the branch of science that focuses on the composition of matter<\/abbr>\u2014the material substances that make up the universe. The basic definition of matter is anything that has mass and takes up space. In short, matter is what the universe is made up of and what we can categorize it into.<\/p>\n

The universe is composed of roughly 109 elements. The basic unit of an element is an atom. Every atom<\/abbr> of each element has the same properties and differs from the atoms of all other elements. A compound<\/abbr> is formed when two or more atoms combine in a fixed proportion, and most substances in our universe have formed compounds.<\/p>\n

If atoms form a unit with a specific number of atoms of two or more elements, the combination is called a molecule<\/abbr>. A molecule is the basic unit of a compound, like water. Some elements also tend to exist as molecules of two or more atoms. Many elements are in their most stable form when they bond with themselves, forming diatomic molecules. Nitrogen and oxygen, two of the most common gases in our atmosphere, are examples of diatomic molecules (N2<\/sub> and O2<\/sub>).<\/p>\n

Matter that has a uniform composition is called a substance<\/abbr>. The key to identifying a substance is that its composition and properties are always the same. Pure water is a substance; apple juice is not. Two samples of apple juice might look and taste very different, depending on the type of apples, the length of time between picking them and pressing for juice, and many other variables.<\/p>\n

There are two kinds of properties that you can use to tell one substance from another\u2014physical properties<\/abbr> and chemical properties<\/abbr>. A physical property can be determined without changing the substance into something else, whereas chemical properties are the substance’s ability to combine with other substances and can only be measured by changing the substance.<\/p>\n

Some of the properties of matter depend on the amount of matter present. These extensive properties<\/abbr> (or extrinsic properties) include its mass and its volume. Other properties, known as intensive properties<\/abbr> (or intrinsic properties) of a substance are independent of the amount of material present. Intensive properties include density, melting point, boiling point, and electrical conductivity.<\/p>\n

Most materials that you use are not pure. Although water is a substance, your tap water is not pure. In addition to water, it contains dissolved minerals — tiny amounts of metals, carbon dioxide, and oxygen from the air. Like apple juice, tap water is a mixture — a combination of two or more substances that retain their individual properties. Homogeneous mixtures<\/abbr> are made of two or more distinct substances, but they have a constant composition within a sample. Clear apple juice is an example of a homogeneous mixture.<\/p>\n

Homogeneous aqueous mixtures are also known as solutions. The term solution<\/abbr> usually refers to a mixture in the liquid state, although homogeneous mixtures of gases or solids can also be called solutions. Heterogeneous mixtures<\/abbr> consist of substances that retain their distinct characteristics and do not blend completely. Orange juice with pulp is an example of a heterogeneous mixture. Although a compound is made of more than one element, a compound is not a mixture. In a compound, atoms are held together in a fixed proportion, making a single chemical substance. In a mixture, two different substances are mixed together, but the proportion can change.<\/p>\n

\n

Question<\/h4>\n

Which of the following is a homogeneous mixture?<\/p>\n

    \n
  1. A chocolate chip cookie<\/li>\n
  2. The air we breathe<\/li>\n
  3. A piece of aluminum foil<\/li>\n
  4. A piece of wood<\/li>\n<\/ol>\n

    Reveal Answer<\/a><\/p>\n

    Choice C is the correct answer. Aluminum foil is a single, uniform substance and the other choices are heterogeneous mixtures.<\/p>\n<\/section>\n

    Atomic Basics<\/h3>\n

    The first subatomic particle to be discovered was the electron<\/abbr>. Electrons have a negative electric charge and a negligible mass. Not long after the electron was discovered, the proton<\/abbr> was also discovered. The proton has a positive charge and is about 1,840 times more massive than an electron. If an atom has equal numbers of protons and electrons (necessary to make it neutral), almost all of its mass consists of protons.<\/p>\n

    After more observations, scientists realized that protons and electrons did not account for all of the mass of an atom. The rest of the mass was made up of a particle called the neutron, an electrically neutral part of each atom’s nucleus. All of the protons and neutrons are clustered together in the center of an atom. This cluster, known as the nucleus, contains almost all of the mass\u2014and very little of the volume\u2014of an atom. The discovery of protons and neutrons, along with the determination that they all cluster together in the center of the atom, led to a model of the atom that looked something like this illustration.<\/p>\n

    \"Helium<\/center>As we know, a theory is modified when new information is obtained. As new data were obtained, the model of the atom changed. The current model is a probabilistic model of electron location. Instead of thinking of electrons as planets orbiting a sun, we currently believe the placement of electrons about the nucleus of an atom is based on cloud-like probability structures, not orbits. It is best to envision different types of electrons in clouds like the diagram below.<\/p>\n

    \"Orbitals\"<\/center>In the modern model of the atom, the electrons are no longer portrayed as moving in fixed orbits around the nucleus. Instead, their position is indicated by a “cloud” that represents a probability of the electron’s position about the nucleus. The farther the electron is located from the nucleus, the higher its level of energy. There is a limit to the number of electrons that can occupy a given energy level. In most atoms, the highest, or outer, energy level can accommodate up to eight electrons. The lowest energy level can only handle two electrons, so hydrogen and helium are exceptions to this octet rule.<\/p>\n

    The number of protons in the atomic nucleus is called the atomic number<\/abbr> of the element. The atomic number of helium is 2. The mass of an atom is located almost entirely in its nucleus. The mass number<\/abbr> of an atom is the sum of the number of protons and the number of neutrons. Most carbon atoms have six neutrons and all carbon atoms have six protons, so most carbon atoms have a mass number of 12.<\/p>\n

    \n

    Question<\/h4>\n

    How many neutrons does an atom of zinc-64, \"Zinc\", have?<\/p>\n

      \n
    1. 30<\/li>\n
    2. 34<\/li>\n
    3. 64<\/li>\n
    4. 94<\/li>\n<\/ol>\n

      Reveal Answer<\/a><\/p>\n

      The correct choice is B. The number of neutrons is the mass number, 64, minus the atomic number, 30.<\/p>\n<\/section>\n

      The Periodic Table<\/h3>\n

      There are a variety of different chemical and physical properties of the elements, but they are patterns of similarity among different elements as well. The periodic table<\/abbr> is a method for organizing the elements based on these similarities.<\/p>\n

      The periodic table is an important tool for all scientific endeavors. Understanding the significance of Groups IA through VIIIA is the key to the rest of the periodic table. The increasing Group A number corresponds to the increasing number of valence (outer) electrons. Group VIIIA elements all (except He) have 8 valence electrons, hence the rule of octet. Helium (He) is such a small atom that only two electrons have room to fit so near the nucleus and fill the outer shell. The elements in Groups IA and IIA easily lose electrons to become positive ions. The tendency to lose electrons easily identifies elements that are commonly called metals. Group IIIA elements tend to lose electrons but not as readily as the Group IA and IIA elements. They often combine with other atoms by sharing electrons. The elements in Group VIA and VIIA easily gain electrons to become negative ions. The tendency to gain electrons easily identifies elements that are commonly called non-metals. The Group V elements tend to gain electrons, but not as readily as Groups VIA and VIIA. They too often combine with other atoms by sharing electrons. The Group IVA elements invariably combine with other atoms by sharing electrons, they do not readily transfer electrons. The Group B elements have more complicated electron structures and will be discussed shortly.<\/p>\n

      Elements in each column of the periodic table exhibit similar properties and are said to be in the same elemental group<\/abbr> or family. For example, sodium and potassium, both in the first column of the table, have very similar chemical and physical properties because they share the same number of electrons in their outermost energy level. They are in Group IA which means they each have one electron in their valence shell.<\/p>\n

      The periodic table is also arranged by increasing atomic number (number of protons) from left to right in each row. Many elements can be classified by their position on the periodic table. Some of the regions of interest are:<\/p>\n

      Metals<\/strong> are the elements on the left and center of the table and the lower section of the right side of the table. Metals tend to be hard, shiny elements that conduct heat and electricity well.<\/p>\n

      Nonmetals<\/strong> are the elements on the right side of the table. Nonmetals form soft, brittle solids. Many of them are gases at room temperature. Nonmetallic elements do not conduct heat or electricity well.<\/p>\n

      Metalloids<\/strong> are the elements in a zigzag line that separates metals and nonmetals. These elements share some properties of both metals and nonmetals.<\/p><\/blockquote>\n

      <\/object><\/p>\n
      \n