Chapter Fifteen: Elements and the Periodic Table 15.1 The Periodic Table of the Elements 15.2 Properties of the Elements

15.1 Physical properties Characteristics that you can see through direct observation are called physical properties. Physical properties include color, texture, density, brittleness, and state (solid, liquid, or gas). Melting point, boiling point, and specific heat are also physical properties.

15.1 Physical properties A physical change does not result in a new substance being formed.

15.1 Chemical properties Properties that can only be observed when one substance changes into a different substance are called chemical properties. Any change that transforms one substance into a different substance is called a chemical change.

15.1 The Periodic Table The periodic table organizes the elements according to how they combine with other elements (chemical properties). The periodic table is organized in order of increasing atomic number.

15.1 The Periodic Table The periodic table is further divided into periods and groups. Each horizontal row is called a period. Each vertical column is called a group.

15.1 The Periodic Table All the elements in Group 1 of the periodic table form similar compounds. The metals lithium, sodium, and potassium all form compounds with a ratio of 2 atoms of the metal to 1 atom of oxygen.

15.1 Atomic Mass The mass of individual atoms is so small that the numbers are difficult to work with. To make calculations easier, scientists use the atomic mass unit (amu). The atomic mass of any element is the average mass (in amu) of an atom of each element.

15.1 Atomic Mass Atomic masses differ from mass numbers because most elements in nature contain more than one isotope.

15.1 Atomic Number Remember, the atomic number is the number of protons all atoms of that element have in their nuclei. If the atom is neutral, it will have the same number of electrons as protons.

15.1 Groups of the periodic table The first group is known as the alkali metals. The alkali metals are soft and silvery in their pure form and are highly reactive. This group includes the elements lithium (Li), sodium (Na), and potassium (K).

15.1 Groups of the periodic table The group two metals include beryllium (Be), magnesium (Mg), and calcium (Ca). They also bond easily with oxygen.

15.1 Halogens The halogens tend to be toxic gases or liquids in their pure form. Fluorine (F), chlorine (Cl), and bromine (Br) form salts when the bond with alkali metals.

15.1 Noble Gases The noble gases, including the elements helium (He), neon (Ne), and argon (Ar). These elements do not naturally form chemical bonds with other atoms and are almost always found in their pure state.

15.2 Properties of the elements Most of the pure elements are solid at room temperature. Only 11 naturally occurring elements are a gas. Only 2 elements (Br and Hg) are liquid at room temperature.

15.2 Periodic properties of elements Periodicity means properties repeat each period (row) of the periodic table.

This pattern is an example of periodicity.

15.2 Thermal and electrical conductivity Electricity is the movement of electric charge, usually electrons. Some materials allow electrons to flow easily through them. We call these materials electrical conductors.

15.2 Thermal and electrical conductivity Like copper, most metals are good thermal conductors. That is one reason pots and pans are made of metal.

15.2 Thermal and electrical conductivity Elements on the far right of the table are called non-metals. Nonmetals make good insulators. An insulator is a material which slows down or stops the flow of either heat or electricity.

15.2 Metals and metal alloys An alloy is a solid mixture of one or more elements. Most metals are used as alloys and not in their pure elemental form. Yellow brass is an alloy of 72% copper, 24% zinc, 3% lead, and 1% tin.

15.2 Metals and metal alloys Titanium combines the strength and hardness of steel with the light weight of aluminum. Titanium, a rare and expensive alloy, is used for military aircraft and racing bicycles.

15.2 Carbon and carbon-like elements Almost all the molecules that make up plants and animals are constructed around carbon. The chemistry of carbon is so important it has its own name, organic chemistry.

15.2 Carbon and carbon-like elements Pure carbon is found in nature as either graphite or diamond. Silicon is the second most abundant element in the Earth’s crust, second only to oxygen. Why are carbon and silicon important?

15.2 Nitrogen, oxygen and phosphorus Oxygen and nitrogen are crucial to living animals and plants. For example, proteins and DNA both contain nitrogen. Phosphorus is a key ingredient of DNA, the molecule responsible for carrying the genetic code in all living creatures.

15.2 Nitrogen, oxygen and phosphorus Proteins and DNA both contain oxygen and nitrogen, making these elements crucial to life. 46% of the mass of Earth’s crust is also oxygen bound up in rocks and minerals.

15.2 Nitrogen, oxygen and phosphorus Phosphorus is a key ingredient of DNA, the molecule responsible for carrying the genetic code in all living creatures. When phosphorus atoms absorb light, they store energy, then release it in a greenish glow.